systematic review type of research

Aims to demonstrate writer has extensively researched literature and critically evaluated its quality. Goes beyond mere description to include degree of analysis and conceptual innovation. Typically results in hypothesis or mode

Seeks to identify most significant items in the field

No formal quality assessment. Attempts to evaluate according to contribution

Typically narrative, perhaps conceptual or chronological

Significant component: seeks to identify conceptual contribution to embody existing or derive new theory

Generic term: published materials that provide examination of recent or current literature. Can cover wide range of subjects at various levels of completeness and comprehensiveness. May include research findings

May or may not include comprehensive searching

May or may not include quality assessment

Typically narrative

Analysis may be chronological, conceptual, thematic, etc.

Map out and categorize existing literature from which to commission further reviews and/or primary research by identifying gaps in research literature

Completeness of searching determined by time/scope constraints

No formal quality assessment

May be graphical and tabular

Characterizes quantity and quality of literature, perhaps by study design and other key features. May identify need for primary or secondary research

Technique that statistically combines the results of quantitative studies to provide a more precise effect of the results

Aims for exhaustive, comprehensive searching. May use funnel plot to assess completeness

Quality assessment may determine inclusion/ exclusion and/or sensitivity analyses

Graphical and tabular with narrative commentary

Numerical analysis of measures of effect assuming absence of heterogeneity

Refers to any combination of methods where one significant component is a literature review (usually systematic). Within a review context it refers to a combination of review approaches for example combining quantitative with qualitative research or outcome with process studies

Requires either very sensitive search to retrieve all studies or separately conceived quantitative and qualitative strategies

Requires either a generic appraisal instrument or separate appraisal processes with corresponding checklists

Typically both components will be presented as narrative and in tables. May also employ graphical means of integrating quantitative and qualitative studies

Analysis may characterise both literatures and look for correlations between characteristics or use gap analysis to identify aspects absent in one literature but missing in the other

Generic term: summary of the [medical] literature that attempts to survey the literature and describe its characteristics

May or may not include comprehensive searching (depends whether systematic overview or not)

May or may not include quality assessment (depends whether systematic overview or not)

Synthesis depends on whether systematic or not. Typically narrative but may include tabular features

Analysis may be chronological, conceptual, thematic, etc.

Method for integrating or comparing the findings from qualitative studies. It looks for ‘themes’ or ‘constructs’ that lie in or across individual qualitative studies

May employ selective or purposive sampling

Quality assessment typically used to mediate messages not for inclusion/exclusion

Qualitative, narrative synthesis

Thematic analysis, may include conceptual models

Assessment of what is already known about a policy or practice issue, by using systematic review methods to search and critically appraise existing research

Completeness of searching determined by time constraints

Time-limited formal quality assessment

Typically narrative and tabular

Quantities of literature and overall quality/direction of effect of literature

Preliminary assessment of potential size and scope of available research literature. Aims to identify nature and extent of research evidence (usually including ongoing research)

Completeness of searching determined by time/scope constraints. May include research in progress

No formal quality assessment

Typically tabular with some narrative commentary

Characterizes quantity and quality of literature, perhaps by study design and other key features. Attempts to specify a viable review

Tend to address more current matters in contrast to other combined retrospective and current approaches. May offer new perspectives

Aims for comprehensive searching of current literature

No formal quality assessment

Typically narrative, may have tabular accompaniment

Current state of knowledge and priorities for future investigation and research

Seeks to systematically search for, appraise and synthesis research evidence, often adhering to guidelines on the conduct of a review

Aims for exhaustive, comprehensive searching

Quality assessment may determine inclusion/exclusion

Typically narrative with tabular accompaniment

What is known; recommendations for practice. What remains unknown; uncertainty around findings, recommendations for future research

Combines strengths of critical review with a comprehensive search process. Typically addresses broad questions to produce ‘best evidence synthesis’

Aims for exhaustive, comprehensive searching

May or may not include quality assessment

Minimal narrative, tabular summary of studies

What is known; recommendations for practice. Limitations

Attempt to include elements of systematic review process while stopping short of systematic review. Typically conducted as postgraduate student assignment

May or may not include comprehensive searching

May or may not include quality assessment

Typically narrative with tabular accompaniment

What is known; uncertainty around findings; limitations of methodology

Specifically refers to review compiling evidence from multiple reviews into one accessible and usable document. Focuses on broad condition or problem for which there are competing interventions and highlights reviews that address these interventions and their results

Identification of component reviews, but no search for primary studies

Quality assessment of studies within component reviews and/or of reviews themselves

Graphical and tabular with narrative commentary

What is known; recommendations for practice. What remains unknown; recommendations for future research

Generic term: published materials that provide an examination of recent or current literature. Can cover a wide range of subjects at various levels of completeness and comprehensiveness. May include research findings

May or may not include comprehensive

searching

May or may not include quality

assessment

Typically narrative

Analysis may be chronological, conceptual, thematic, etc.

Seeks to systematically search for, appraise and synthesize research evidence, often adhering to guidelines on the conduct of a review

Aims for exhaustive,

Comprehensive searching

Quality assessment

may determine

inclusion/exclusion

Typically narrative

with tabular

accompaniment

What is known; recommendations

for practice. What remains unknown; uncertainty around findings, recommendations for

future research

Technique that statistically combines the results of quantitative studies to provide a more precise effect of the results

Aims for exhaustive searching. May use funnel plot to assess completeness

Quality assessment may determine inclusion/exclusion and/or sensitivity analyses

Graphical and tabular with narrative commentary

Numerical analysis of measures of effect assuming absence of heterogeneity

Preliminary assessment of potential size and scope of available research literature. Aims to identify the nature and extent of research evidence (usually including ongoing research)

Completeness of searching determined by time/scope constraints. May include research in progress

No formal quality assessment

Typically tabular with some narrative commentary

Characterizes quantity and quality of literature, perhaps by study design and other key features. Attempts to specify a viable review

Refers to any combination of methods where one significant component is a literature review (usually systematic). Within a review context, it refers to a combination of review approaches for example combining quantitative with qualitative research or outcome with process studies

Requires either very sensitive search to retrieve all studies or separately conceived quantitative and qualitative strategies

Requires either a generic appraisal instrument or separate appraisal processes with corresponding checklists

Typically both components will be presented as narrative and in tables. May also employ graphical means of integrating quantitative and qualitative studies

Analysis may characterize both works of literature and look for correlations between characteristics or use gap analysis to identify aspects absent in one literature but missing in the other

Specifically refers to review compiling evidence from multiple reviews into one accessible and usable document. Focuses on a broad condition or problem for which there are competing interventions and highlights reviews that address these interventions and their results

Identification of component reviews, but no search for primary studies

Quality assessment of studies within component reviews and/or of reviews themselves

Graphical and tabular with narrative commentary

What is known; recommendations for practice. What remains unknown; recommendations for future research

Reproduced from Grant MJ, Booth A. A typology of reviews: an analysis of 14 review types and associated methodologies . Health Info Libr J. 2009 Jun;26(2):91-108. doi: 10.1111/j.1471-1842.2009.00848.x

• Last Updated: Aug 12, 2024 8:26 AM
• URL: https://guides.lib.utexas.edu/systematicreviews

Systematic Reviews for Non-Health Sciences

• Getting started

Types of reviews and examples

Choosing a review type.

• 0. Planning the systematic review
• 1. Formulating the research question
• 2. Developing the protocol
• 3. Searching, screening, and selection of articles
• 4. Critical appraisal
• 5. Writing and publishing
• Guidelines & standards
• Software and tools
• Software tutorials
• Resources by discipline
• Duke Med Center Library: Systematic reviews This link opens in a new window
• Overwhelmed? General literature review guidance This link opens in a new window

Email a Librarian

Contact a Librarian

Ask a Librarian

• Meta-analysis
• Systematized

Definition:

"A term used to describe a conventional overview of the literature, particularly when contrasted with a systematic review (Booth et al., 2012, p. 265).

Characteristics:

• Provides examination of recent or current literature on a wide range of subjects
• Varying levels of completeness / comprehensiveness, non-standardized methodology
• May or may not include comprehensive searching, quality assessment or critical appraisal

Mitchell, L. E., & Zajchowski, C. A. (2022). The history of air quality in Utah: A narrative review.  Sustainability ,  14 (15), 9653.  doi.org/10.3390/su14159653

Booth, A., Papaioannou, D., & Sutton, A. (2012). Systematic approaches to a successful literature review. London: SAGE Publications Ltd.

"An assessment of what is already known about a policy or practice issue...using systematic review methods to search and critically appraise existing research" (Grant & Booth, 2009, p. 100).

• Assessment of what is already known about an issue
• Similar to a systematic review but within a time-constrained setting
• Typically employs methodological shortcuts, increasing risk of introducing bias, includes basic level of quality assessment
• Best suited for issues needing quick decisions and solutions (i.e., policy recommendations)

Learn more about the method:

Khangura, S., Konnyu, K., Cushman, R., Grimshaw, J., & Moher, D. (2012). Evidence summaries: the evolution of a rapid review approach.  Systematic reviews, 1 (1), 1-9.  https://doi.org/10.1186/2046-4053-1-10

Virginia Commonwealth University Libraries. (2021). Rapid Review Protocol .

Quarmby, S., Santos, G., & Mathias, M. (2019). Air quality strategies and technologies: A rapid review of the international evidence.  Sustainability, 11 (10), 2757.  https://doi.org/10.3390/su11102757

Grant, M.J. & Booth, A. (2009). A typology of reviews: an analysis of the 14 review types and associated methodologies.  Health Information & Libraries Journal , 26(2), 91-108. https://www.doi.org/10.1111/j.1471-1842.2009.00848.x

Developed and refined by the Evidence for Policy and Practice Information and Co-ordinating Centre (EPPI-Centre), this review "map[s] out and categorize[s] existing literature on a particular topic, identifying gaps in research literature from which to commission further reviews and/or primary research" (Grant & Booth, 2009, p. 97).

Although mapping reviews are sometimes called scoping reviews, the key difference is that mapping reviews focus on a review question, rather than a topic

Mapping reviews are "best used where a clear target for a more focused evidence product has not yet been identified" (Booth, 2016, p. 14)

Mapping review searches are often quick and are intended to provide a broad overview

Mapping reviews can take different approaches in what types of literature is focused on in the search

Cooper I. D. (2016). What is a "mapping study?".  Journal of the Medical Library Association: JMLA ,  104 (1), 76–78. https://doi.org/10.3163/1536-5050.104.1.013

Miake-Lye, I. M., Hempel, S., Shanman, R., & Shekelle, P. G. (2016). What is an evidence map? A systematic review of published evidence maps and their definitions, methods, and products.  Systematic reviews, 5 (1), 1-21.  https://doi.org/10.1186/s13643-016-0204-x

Tainio, M., Andersen, Z. J., Nieuwenhuijsen, M. J., Hu, L., De Nazelle, A., An, R., ... & de Sá, T. H. (2021). Air pollution, physical activity and health: A mapping review of the evidence.  Environment international ,  147 , 105954.  https://doi.org/10.1016/j.envint.2020.105954

Booth, A. (2016). EVIDENT Guidance for Reviewing the Evidence: a compendium of methodological literature and websites . ResearchGate. https://doi.org/10.13140/RG.2.1.1562.9842 . 

Grant, M.J. & Booth, A. (2009). A typology of reviews: an analysis of the 14 review types and associated methodologies.  Health Information & Libraries Journal , 26(2), 91-108.  https://www.doi.org/10.1111/j.1471-1842.2009.00848.x

"A type of review that has as its primary objective the identification of the size and quality of research in a topic area in order to inform subsequent review" (Booth et al., 2012, p. 269).

• Main purpose is to map out and categorize existing literature, identify gaps in literature—great for informing policy-making
• Search comprehensiveness determined by time/scope constraints, could take longer than a systematic review
• No formal quality assessment or critical appraisal

Learn more about the methods :

Arksey, H., & O'Malley, L. (2005) Scoping studies: towards a methodological framework.  International Journal of Social Research Methodology ,  8 (1), 19-32.  https://doi.org/10.1080/1364557032000119616

Levac, D., Colquhoun, H., & O’Brien, K. K. (2010). Scoping studies: Advancing the methodology. Implementation Science: IS, 5, 69. https://doi.org/10.1186/1748-5908-5-69

Example : 

Rahman, A., Sarkar, A., Yadav, O. P., Achari, G., & Slobodnik, J. (2021). Potential human health risks due to environmental exposure to nano-and microplastics and knowledge gaps: A scoping review.  Science of the Total Environment, 757 , 143872.  https://doi.org/10.1016/j.scitotenv.2020.143872

A review that "[compiles] evidence from multiple...reviews into one accessible and usable document" (Grant & Booth, 2009, p. 103). While originally intended to be a compilation of Cochrane reviews, it now generally refers to any kind of evidence synthesis.

• Compiles evidence from multiple reviews into one document
• Often defines a broader question than is typical of a traditional systematic review

Choi, G. J., & Kang, H. (2022). The umbrella review: a useful strategy in the rain of evidence.  The Korean Journal of Pain ,  35 (2), 127–128.  https://doi.org/10.3344/kjp.2022.35.2.127

Aromataris, E., Fernandez, R., Godfrey, C. M., Holly, C., Khalil, H., & Tungpunkom, P. (2015). Summarizing systematic reviews: Methodological development, conduct and reporting of an umbrella review approach. International Journal of Evidence-Based Healthcare , 13(3), 132–140. https://doi.org/10.1097/XEB.0000000000000055

Rojas-Rueda, D., Morales-Zamora, E., Alsufyani, W. A., Herbst, C. H., Al Balawi, S. M., Alsukait, R., & Alomran, M. (2021). Environmental risk factors and health: An umbrella review of meta-analyses.  International Journal of Environmental Research and Public Dealth ,  18 (2), 704.  https://doi.org/10.3390/ijerph18020704

A meta-analysis is a "technique that statistically combines the results of quantitative studies to provide a more precise effect of the result" (Grant & Booth, 2009, p. 98).

• Statistical technique for combining results of quantitative studies to provide more precise effect of results
• Aims for exhaustive, comprehensive searching
• Quality assessment may determine inclusion/exclusion criteria
• May be conducted independently or as part of a systematic review

Berman, N. G., & Parker, R. A. (2002). Meta-analysis: Neither quick nor easy. BMC Medical Research Methodology , 2(1), 10. https://doi.org/10.1186/1471-2288-2-10

Hites R. A. (2004). Polybrominated diphenyl ethers in the environment and in people: a meta-analysis of concentrations.  Environmental Science & Technology ,  38 (4), 945–956.  https://doi.org/10.1021/es035082g

A systematic review "seeks to systematically search for, appraise, and [synthesize] research evidence, often adhering to the guidelines on the conduct of a review" provided by discipline-specific organizations, such as the Cochrane Collaboration (Grant & Booth, 2009, p. 102).

• Aims to compile and synthesize all known knowledge on a given topic
• Adheres to strict guidelines, protocols, and frameworks
• Time-intensive and often takes months to a year or more to complete
• The most commonly referred to type of evidence synthesis. Sometimes confused as a blanket term for other types of reviews

Gascon, M., Triguero-Mas, M., Martínez, D., Dadvand, P., Forns, J., Plasència, A., & Nieuwenhuijsen, M. J. (2015). Mental health benefits of long-term exposure to residential green and blue spaces: a systematic review.  International Journal of Environmental Research and Public Health ,  12 (4), 4354–4379.  https://doi.org/10.3390/ijerph120404354

"Systematized reviews attempt to include one or more elements of the systematic review process while stopping short of claiming that the resultant output is a systematic review" (Grant & Booth, 2009, p. 102). When a systematic review approach is adapted to produce a more manageable scope, while still retaining the rigor of a systematic review such as risk of bias assessment and the use of a protocol, this is often referred to as a  structured review  (Huelin et al., 2015).

• Typically conducted by postgraduate or graduate students
• Often assigned by instructors to students who don't have the resources to conduct a full systematic review

Salvo, G., Lashewicz, B. M., Doyle-Baker, P. K., & McCormack, G. R. (2018). Neighbourhood built environment influences on physical activity among adults: A systematized review of qualitative evidence.  International Journal of Environmental Research and Public Health ,  15 (5), 897.  https://doi.org/10.3390/ijerph15050897

Huelin, R., Iheanacho, I., Payne, K., & Sandman, K. (2015). What’s in a name? Systematic and non-systematic literature reviews, and why the distinction matters. https://www.evidera.com/resource/whats-in-a-name-systematic-and-non-systematic-literature-reviews-and-why-the-distinction-matters/

• Review Decision Tree - Cornell University For more information, check out Cornell's review methodology decision tree.
• LitR-Ex.com - Eight literature review methodologies Learn more about 8 different review types (incl. Systematic Reviews and Scoping Reviews) with practical tips about strengths and weaknesses of different methods.
• Right Review This tool is designed to provide guidance and supporting material to reviewers on methods for the conduct and reporting of knowledge synthesis.
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• Last Updated: Jul 26, 2024 10:38 AM
• URL: https://guides.library.duke.edu/systematicreviews

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Systematic reviews and other evidence synthesis projects

Types of reviews, a summary of review types, further reading on review types.

• Systematic Reviews
• 0. Plan your Review
• 1. Define the Question
• 2. Check for Recent Systematic Reviews and Protocols
• 3. Write and register your protocol
• Developing your Search Terms
• Database Search Tips and Filters
• Grey Literature
• Record and Report your Search Strategy
• Covidence This link opens in a new window
• 6. Appraise the Studies
• 7. Extract Data
• 8. Analyze / Synthesize Data
• 9. Write the Review
• Rapid Reviews
• Scoping Reviews
• Equity in Evidence Synthesis
• Automation, AI, and other upcoming review technologies
• Librarian Support

Although systematic reviews are one of the most well-known review types, there are a variety of different types of reviews that vary in terms of scope, comprehensiveness, time constraints, and types of studies included.

The best review for your project depends on the intersection of:

• your research goals
• your research question
• your time frame
• your research team

Several tools are provided below to help you identify which type of review is best suited for your research.

Identifying the right review type for your project - start here!

• Review Methodology Decision Tree from Cornell University Library
• Flow chart for selecting review type from Yale's Cushing/Whitney Medical Library
• What review is right for you? is a tool to help guide your choice of an appropriate knowledge synthesis method when looking at quantitative studies.

Based on University of North Carolina at Chapel Hill Health Sciences Library. Types of Reviews. Systematic Reviews website. Updated January 29, 2021. Accessed September 21, 2021. https://guides.lib.unc.edu/systematic-reviews

• Meeting the review family: exploring review types and associated information retrieval requirements ; by Sutton A, Clowes M, Preston L, Booth A. Health Info Libr J . 2019;36(3):202-222. doi:10.1111/hir.12276
• A typology of reviews: an analysis of 14 review types and associated methodologies ; by Grant MJ, Booth A. Health Info Libr J . 2009;26(2):91-108. doi:10.1111/j.1471-1842.2009.00848.x
• Systematic review or scoping review? Guidance for authors when choosing between a systematic or scoping review approach ; by Zachary Munn, Micah D. J. Peters, Cindy Stern, Catalin Tufanaru, Alexa McArthur & Edoardo Aromataris. BMC Med Res Methodol 18, 143 (2018). https://doi.org/10.1186/s12874-018-0611-x
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• Next: Systematic Reviews >>
• Last Updated: Jul 29, 2024 9:16 AM
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Systematic Reviews

Describes what is involved with conducting a systematic review of the literature for evidence-based public health and how the librarian is a partner in the process.

Several CDC librarians have special training in conducting literature searches for systematic reviews.  Literature searches for systematic reviews can take a few weeks to several months from planning to delivery.

Fill out a search request form here  or contact the Stephen B. Thacker CDC Library by email  [email protected] or telephone 404-639-1717.

Campbell Collaboration

Cochrane Collaboration

Eppi Centre

Joanna Briggs Institute

McMaster University

PRISMA Statement

Systematic Reviews – CRD’s Guide

Systematic Reviews of Health Promotion and Public Health Interventions

The Guide to Community Preventive Services

Look for systematic reviews that have already been published. 

• To ensure that the work has not already been done.
• To provides examples of search strategies for your topic

Look in PROSPERO for registered systematic reviews.

Search Cochrane and CRD-York for systematic reviews.

Search filter for finding systematic reviews in PubMed

Other search filters to locate systematic reviews

A systematic review attempts to collect and analyze all evidence that answers a specific question.  The question must be clearly defined and have inclusion and exclusion criteria. A broad and thorough search of the literature is performed and a critical analysis of the search results is reported and ultimately provides a current evidence-based answer  to the specific question.

Time:  According to Cochrane , it takes 18 months on average to complete a Systematic Review.

The average systematic review from beginning to end requires 18 months of work. “…to find out about a healthcare intervention it is worth searching research literature thoroughly to see if the answer is already known. This may require considerable work over many months…” ( Cochrane Collaboration )

Review Team: Team Members at minimum…

• Content expert
• 2 reviewers
• 1 tie breaker
• 1 statistician (meta-analysis)
• 1 economist if conducting an economic analysis
• *1 librarian (expert searcher) trained in systematic reviews

“Expert searchers are an important part of the systematic review team, crucial throughout the review process-from the development of the proposal and research question to publication.” ( McGowan & Sampson, 2005 )

*Ask your librarian to write a methods section regarding the search methods and to give them co-authorship. You may also want to consider providing a copy of one or all of the search strategies used in an appendix.

The Question to Be Answered: A clearly defined and specific question or questions with inclusion and exclusion criteria.

Written Protocol: Outline the study method, rationale, key questions, inclusion and exclusion criteria, literature searches, data abstraction and data management, analysis of quality of the individual studies, synthesis of data, and grading of the evidience for each key question.

Literature Searches:  Search for any systematic reviews that may already answer the key question(s).  Next, choose appropriate databases and conduct very broad, comprehensive searches.  Search strategies must be documented so that they can be duplicated.  The librarian is integral to this step of the process. Before your librarian creates a search strategy and starts searching in earnest you should write a detailed PICO question , determine the inclusion and exclusion criteria for your study, run a preliminary search, and have 2-4 articles that already fit the criteria for your review.

What is searched depends on the topic of the review but should include…

• At least 3 standard medical databases like PubMed/Medline, CINAHL, Embase, etc..
• At least 2 grey literature resources like Clinicaltrials.gov, COS Conference Papers Index, Grey Literature Report,  etc…

Citation Management: EndNote is a bibliographic management tools that assist researchers in managing citations.  The Stephen B. Thacker CDC Library oversees the site license for EndNote.

To request installation:   The library provides EndNote  to CDC staff under a site-wide license. Please use the ITSO Software Request Tool (SRT) and submit a request for the latest version (or upgraded version) of EndNote. Please be sure to include the computer name for the workstation where you would like to have the software installed.

EndNote Training:   CDC Library offers training on EndNote on a regular basis – both a basic and advanced course. To view the course descriptions and upcoming training dates, please visit the CDC Library training page .

For assistance with EndNote software, please contact [email protected]

Vendor Support and Services:   EndNote – Support and Services (Thomson Reuters)  EndNote – Tutorials and Live Online Classes (Thomson Reuters)

Getting Articles:

Articles can be obtained using DocExpress or by searching the electronic journals at the Stephen B. Thacker CDC Library.

IOM Standards for Systematic Reviews: Standard 3.1: Conduct a comprehensive systematic search for evidence

The goal of a systematic review search is to maximize recall and precision while keeping results manageable. Recall (sensitivity) is defined as the number of relevant reports identified divided by the total number of relevant reports in existence. Precision (specificity) is defined as the number of relevant reports identified divided by the total number of reports identified.

Issues to consider when creating a systematic review search:   

• All concepts are included in the strategy
• All appropriate subject headings are used
• Appropriate use of explosion
• Appropriate use of subheadings and floating subheadings
• Use of natural language (text words) in addition to controlled vocabulary terms
• Use of appropriate synonyms, acronyms, etc.
• Truncation and spelling variation as appropriate
• Appropriate use of limits such as language, years, etc.
• Field searching, publication type, author, etc.
• Boolean operators used appropriately
• Line errors: when searches are combined using line numbers, be sure the numbers refer to the searches intended
• Check indexing of relevant articles
• Search strategy adapted as needed for multiple databases
• Cochrane Handbook: Searching for Studies See Part 2, Chapter 6

A step-by-step guide to systematically identify all relevant animal studies

Materials listed in these guides are selected to provide awareness of quality public health literature and resources. A material’s inclusion does not necessarily represent the views of the U.S. Department of Health and Human Services (HHS), the Public Health Service (PHS), or the Centers for Disease Control and Prevention (CDC), nor does it imply endorsement of the material’s methods or findings. HHS, PHS, and CDC assume no responsibility for the factual accuracy of the items presented. The selection, omission, or content of items does not imply any endorsement or other position taken by HHS, PHS, and CDC. Opinion, findings, and conclusions expressed by the original authors of items included in these materials, or persons quoted therein, are strictly their own and are in no way meant to represent the opinion or views of HHS, PHS, or CDC. References to publications, news sources, and non-CDC Websites are provided solely for informational purposes and do not imply endorsement by HHS, PHS, or CDC.

Eccles Health Sciences Library

Spencer s. eccles health sciences library.

• University of Utah
• ULibraries Research Guides
• * Eccles Health Sciences Library Research Guides

Systematic Reviews

Choosing a review type.

• Systematic Review Process: At a Glance
• Learn Systematic Reviews
• Appraise Systematic Reviews
• Conducting Scoping Reviews

Review types and evidence level

Selected review types, additional discussion of review types, involve a librarian.

• ULibraries Evidence Review Services

Not every research question requires systematic review methodology.

Be sure to select the review type that matches the purpose and scope of your project., all reviews should be methodical - conducted in a careful and deliberate manner.  , questions to ask yourself:, what is the purpose of this review , what is the research question, how long do i have to complete it, am i doing it alone or part of a team, how much of the literature do i need to capture, do my literature search and methods need  to be transparent and replicable.

Right Review -   a tool providing guidance and supporting material on methods for conduct and reporting of knowledge synthesis.

Reviews of increasing complexity, from narrative reviews to systematic reviews... with complexity comes an increase in time & resources needed. -from Scoping Studies. Health Libraries Portal . HLWIKI International

Narrative Reviews or Literature Reviews

• Useful in tracing concept development
• Scope can be broad or focused
• Methodology is not standardized 
• Can be conducted by an individual or a team
• Journal requirements vary -  check the journal's instruction for authors

Making literature reviews more reliable through application of lessons from systematic reviews. Haddaway NR, Woodcock P, Macura B, Collins A. Conserv Biol. 2015;29(6):1596-605. Epub 20150601. doi: 10.1111/cobi.12541. PubMed PMID: 26032263.

SANRA-a scale for the quality assessment of narrative review articles. Baethge C, Goldbeck-Wood S, Mertens S.  Res Integr Peer Rev. 2019;4:5. Epub 20190326. doi: 10.1186/s41073-019-0064-8. PubMed PMID: 30962953; PubMed Central PMCID: PMC643487

Time to challenge the spurious hierarchy of systematic over narrative reviews? Greenhalgh T, Thorne S, Malterud K.  Eur J Clin Invest. 2018;48(6):e12931. Epub 2018/03/27. doi: 10.1111/eci.12931. PubMed PMID: 29578574; PubMed Central PMCID: PMC6001568.

Evidence Reviews listed below which utilize explicit methodologies, reduce bias, increase transparency & reproducibility and a team.

• Addresses a specific question
• Uses specified methodology to reduce bias
• Requires a team and time commitment
• May include meta-analysis, dependent upon heterogeneity

Systematic review or scoping review? Guidance for authors when choosing between a systematic or scoping review approach.  Munn Z, Peters MDJ, Stern C, Tufanaru C, McArthur A, Aromataris E.     BMC Med Res Methodol. Nov 19 2018;18(1):143. doi:10.1186/s12874-018-0611-x

What kind of systematic review should I conduct? A proposed typology and guidance for systematic reviewers in the medical and health sciences . Munn, Z., Stern, C., Aromataris, E. et al.  BMC Med Res Methodol 18, 5 (2018). doi:10.1186/s12874-017-0468-4  

Conducting a systematic review: finding the evidence . Lodge, M. (2011). J Evid Based Med, 4(2), 135-139. doi: 10.1111/j.1756-5391.2011.01130.x PubMed PMID: 23672704

Reviews of Reviews (Umbrella)

• Systematic review using only systematic reviews as subjects
• Synthesizes systematic reviews of same topic
• Assesses scope and quality of individual systematic reviews

Conducting umbrella reviews. Belbasis L, Bellou V, Ioannidis JPA.  BMJ Medicine. 2022;1(1). doi: 10.1136/bmjmed-2021-000071. PubMed PMID: 36936579

Methodology in conducting a systematic review of systematic reviews of healthcare interventions . Smith V, Devane D, Begley CM, Clarke M. BMC Med Res Methodol. 2011 Feb 3;11(1):15. doi: 10.1186/1471-2288-11-15.

Scoping Reviews

• Looks at broad research question
• Creates broad literature map to find gaps
• Requires a team and time
• Uses qualitative analysis

What are scoping reviews? Providing a formal definition of scoping reviews as a type of evidence synthesis. Munn Z, Pollock D, Khalil H, Alexander L, McLnerney P, Godfrey CM, et al.  JBI Evid Synth. 2022;20(4):950-2. Epub 20220401. doi: 10.11124/JBIES-21-00483. PubMed PMID: 35249995 .

Conducting high quality scoping reviews-challenges and solution s. Khalil H, Peters MD, Tricco AC, Pollock D, Alexander L, McInerney P, et al.  J Clin Epidemiol. 2020. Epub 2020/10/31. doi: 10.1016/j.jclinepi.2020.10.009. PubMed PMID: 33122034

Realist Reviews

• Focuses on context and process
• Uses an iterative protocol
• Useful for complex policy interventions     

Realist synthesis: illustrating the method for implementation research . Rycroft-Malone J, McCormack B, Hutchinson AM, DeCorby K, Bucknall TK, Kent B, Schultz A, Snelgrove-Clarke E, Stetler CB, Titler M, Wallin L, Wilson V. Implement Sci.2012 Apr 19;7:33. doi: 10.1186/1748-5908-7-33.

Rapid Reviews

• Used on emerging issues needing quick answers
• Uses systematic review methods
• Time constraints (often ≤3 months)

Evidence summaries: the evolution of a rapid review approach . Khangura S, Konnyu K, Cushman R, Grimshaw J, Moher D. Syst Rev. 2012 Feb 10;1:10. doi:10.1186/2046-4053-1-10.

Moher D, Stewart L, Shekelle P. All in the Family: systematic reviews, rapid reviews, scoping reviews, realist reviews, and more . Syst Rev. 2015 Dec 22;4:183.doi: 10.1186/s13643-015-0163-7. PubMed PMID: 26693720 ; PubMed Central PMCID: PMC4688988.

Grant MJ, Booth A. A typology of reviews: an analysis of 14 review types and associated methodologies . Health Info Libr J. 2009 Jun;26(2):91-108. doi:10.1111/j.1471-1842.2009.00848.x. PubMed PMID: 1949148

Fourteen review types and associated methodologies were compared and contrasted using  the SALSA (Search, AppraisaL, Synthesis and Analysis) framework.

Rethlefsen ML, Murad MH, Livingston EH. Engaging Medical Librarians to Improve the Quality of Review Articles . JAMA. 2014 Sep 10;312(10):999-1000. PubMed PMID: 25203078

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Systematic Reviews

• Introduction

Guidance on Methodologies

Scoping reviews, integrative reviews, rapid reviews, literature review, structured literature review, living systematic reviews.

• About Meta-Analysis
• Planning a Review
• Other Guidelines
• Protocol Registration
• Hedges & Literature Searching
• Grey Literature This link opens in a new window
• Quality Assessment Tools
• For Librarians

• Right Review (online tool) "This tool is designed to provide guidance and supporting material to reviewers on methods for the conduct and reporting of knowledge synthesis." Dr. Andrea Tricco
• What Type of Review is Right for You? From Cornell University Library
• A typology of reviews: an analysis of 14 review types and associated methodologies Grant MJ, Booth A. Health Info Libr J. 2009 Jun;26(2):91-108. PMID: 19490148
• Meeting the review family: exploring review types and associated information retrieval requirements. Sutton A, Clowes M, Preston L, Booth A. Health Info Libr J. 2019 Sep;36(3):202-222.
• Systematic review or scoping review? Guidance for authors when choosing between a systematic or scoping review approach. Munn, Z. 2018 BMC Medical Research Methodology, 18(1), 143. PMID: 30453902
• Systematic Reviews (OA journal)
• JBI Manual for Evidence Synthesis Aromataris E, Munn Z (Editors). JBI Manual for Evidence Synthesis. JBI, 2020. more... less... For systematic reviews of: • Qualitative evidence • Effectiveness • Text and Opinion • Prevalence and Incidence • Economic evidence • Etiology and Risk • Mixed methods • Diagnostic test accuracy • Umbrella reviews • Scoping reviews • Measurement properties
• Summary of research that addresses a focused clinical question in a systematic reproducible manner.
• Requires a team of at least three members to screen and adjudicate included articles.
• Includes a clearly defined research question formulated in a PICO framework.
• Requires a written protocol that may be registered with PROSPERO or another registration agency.
• Includes a systematic and replicable search strategy using multiple databases. Often two of the following:
• PubMed/MEDLINE
• Web of Science

plus a subject-specific database such as:

• CABI Global Health
• APA PsycInfo
• Often also includes a search for grey literature and hand-searching methods.
• Generally follows reporting guidelines such as PRISMA .
• A 24-step guide on how to design, conduct, and successfully publish a systematic review and meta-analysis in medical research. Muka, T., Glisic, M., Milic, J., Verhoog, S., Bohlius, J., Bramer, W., Chowdhury, R., & Franco, O. H. (2020). European journal of epidemiology, 35(1), 49–60. PMID: 31720912
• Cochrane Handbook for Systematic Reviews of Interventions (V. 6)
• Guidance to best tools and practices for systematic reviews. Kolaski K, Logan LR, Ioannidis JPA. Syst Rev. 2023 Jun 8;12(1):96. PMID: 37291658.

• A literature review that is performed to rapidly outline the breadth, depth and type of literature available regarding a particular research topic.
• An attempt to map out the evidence based on a research topic.
• The completeness of the search is dictated by time restraints. This type of search may include research in progress.
• JBI - Scoping Reviews Peters MDJ, Godfrey C, McInerney P, Munn Z, Tricco AC, Khalil, H. Scoping Reviews (2020). Aromataris E, Lockwood C, Porritt K, Pilla B, Jordan Z, editors. JBI Manual for Evidence Synthesis. JBI; 2024
• Updated methodological guidance for the conduct of scoping reviews. Peters MDJ, Marnie C, Tricco AC, Pollock D, Munn Z, Alexander L, McInerney P, Godfrey CM, Khalil H. JBI Evid Implement. 2021 Mar;19(1):3-10. doi: 10.1097/XEB.0000000000000277. PMID: 33570328.
• Methods for Research Evidence Synthesis: The Scoping Review Approach Sucharew, H., & Macaluso, M. (2019). Journal of hospital medicine, 14(7), 416–418. https://doi.org/10.12788/jhm.3248
• Scoping Studies: Towards a Methodological Framework. Arksey, H., & O’Malley, L. Intl Journal of Social Research Methodology, 2005 8(1), 19–32.
• Reviews that include both qualitative and quantitative evidence.
• May be useful in research areas where there are few published trials.
• May include literature from experimental and non-experimental research methodologies.
• Often implemented by the nursing research community.

• Chapter 10: Integrative Review In Cheryl Holly, E. R. A. F. (2019). Practice-Based Scholarly Inquiry and the DNP Project. 2nd edition.
• Writing Integrative Literature Reviews: Guidelines and Examples Torraco, R. J. (2005). Writing Integrative Literature Reviews: Guidelines and Examples. Human Resource Development Review, 4(3), 356–367.
• The integrative review: updated methodology. Whittemore, R., & Knafl, K. (2005). The integrative review: updated methodology. Journal of advanced nursing, 52(5), 546–553.
• Reviews that generally follow the guidelines of a systematic review, but are conducted in a condensed time by implementing documented time-saving measures.
• Searching only one database.
• Narrow search time frame.
• Reliance on published material only.
• Use of a single screener.
• Rapid Review Guidebook From the National Collaborating Centre of Methods and Tools.
• Reviews: Rapid! Rapid! Rapid! …and systematic Holger J Schünemann and Lorenzo Moja. Systematic Reviews 2015 4:4.
• Expediting Systematic Reviews: Methods and Implications of Rapid Reviews Ganann, R., Ciliska, D., & Thomas, H. (2010). Implementation science: 5, 56.
• A scoping review of rapid review methods. Tricco AC, Antony J, et al. BMC Med. 2015 Sep 16;13:224.
• A general term that describes a study that assimilates, synthesizes or describes the findings of more than one study or review.
• This is a review with a wide scope and non-standardized methodology. Synthesis is typically narrative.
• The literature search does not need to be comprehensive or systematic.
• These reviews typically do not attempt to address a single research question, but are more broad in scope and have no explicit criteria for inclusion.
• Also known as a Systematized Review.
• Not formally defined.
• Usually attempts to include elements of the systematic review process.
• Often conducted as a postgraduate assignment or thesis.

"We define an LSR as a systematic review which is continually updated, incorporating relevant new evidence as it becomes available." - Cochrane Living Evidence Network

• Feasibility and acceptability of living systematic reviews: results from a mixed-methods evaluation Tanya Millard et al. Systematic Reviews volume 8, 325 (2019).
• Living systematic review: 1. Introduction-the why, what, when, and how. Elliott, J. H., & Living Systematic Review Network (2017). Journal of clinical epidemiology, 91, 23–30.
• Boland, A., Cherry, M. G., & Dickson, R. (2014). Doing a systematic review: a student's guide. London; Thousand Oakes, California: SAGE.
• Colquhoun, H. L., Levac, D., O'Brien, K. K., Straus, S., Tricco, A. C., Perrier, L., . . . Moher, D. (2014). Scoping reviews: time for clarity in definition, methods, and reporting. J Clin Epidemiol, 67(12), 1291-1294. doi:10.1016/j.jclinepi.2014.03.013
• Foster, M. J., & Jewell, S. T. (2017). Assembling the pieces of a systematic review: guide for librarians. Lanham: Rowman & Littlefield.  Full text for Emory Users
• Grant, M. J., & Booth, A. (2009). A typology of reviews: an analysis of 14 review types and associated methodologies. Health Info Libr J, 26(2), 91-108. doi:10.1111/j.1471-1842.2009.00848.x
• Guyatt, G., Rennie, D., Meade, M., Cook, D., & American Medical Association. (2015). Users' guides to the medical literature. A manual for evidence-based clinical practice (Third edition. ed.). New York: McGraw-Hill Education Medical.  Full Text for Emory Users
• Hopia, H., Latvala, E., & Liimatainen, L. (2016). Reviewing the methodology of an integrative review. Scand J Caring Sci, 30(4), 662-669. doi:10.1111/scs.12327
• Library, B. U. Systematic and Literature Reviews. Retrieved from http://libguides.brown.edu/Reviews/types
• Whittemore, R., & Knafl, K. (2005). The integrative review: updated methodology. J Adv Nurs, 52(5), 546-553. doi:10.1111/j.1365-2648.2005.03621.x
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Impacts of long-term transit system disruptions and transitional periods on travelers: a systematic review

• Open access
• Published: 27 August 2024
• Volume 1 , article number  15 , ( 2024 )

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• Mohamed G. Noureldin 1 &
• Ehab Diab 1  

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Governments around the world are heavily investing in building new transit infrastructures and expanding existing ones. The construction of these projects does not happen overnight and can lead to extended long-term disruptions in the transit network, which can have undesirable impacts. Research regarding such disruptive periods, or transitional periods, seems to be thematically and geographically dispersed in the literature. Similarly, a consolidated understanding of the impacts of long-term transit service disruptions due to other causes, such as labor strikes and transit system failures, on travelers’ behavior seems missing from the literature. Using a systematic review method, this study aims at providing a comprehensive review of the academic literature that focused on analyzing the impacts of the aforementioned issues on transit users’ travel behavior and perceptions, while understanding the mitigation strategies applied to address these effects. Given the wide array of disruption types, durations, spatial coverage, and the modes affected, the review indicates a dearth of knowledge regarding their impacts along with a very limited understanding of the relative benefits of mitigation strategies. The most common impacts are mode changes. Some evidence, which is rather limited, shows that transit users did return to their previous travel behavior after the end of long-term service disruptions. The study offers a better understanding of the relative impacts of transit systems’ long-term disruptions and transitional periods, while highlighting important gaps in the current literature.

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1 Introduction

Governments around the world are heavily investing in building new transit infrastructure or upgrading or expanding existing ones [ 1 , 2 ]. This is in order to draw higher levels of transit ridership, while decreasing the attractiveness of non-sustainable modes of transport (such as private car use). Achieving these goals would help societies in reaching their emerging climate goals by reducing the emissions from the transport sector. The construction of these new transit projects does not happen overnight and can take from a few weeks to several months or even years, which can lead to extended long-term disruptions in the transit network. These long-term disruptions, or transitional periods, can have undesirable impacts on people’s travel behavior, and they could also increase traffic congestion as well as decrease air quality in the short and long terms. The impacts of these transitional periods, in general, seem thematically and geographically dispersed. Similarly, a consolidated understanding of the impacts of long-term disruptions due to other causes, such as labor strikes and transit system failures, on travelers’ behavior seems to be missing from the literature. Albeit different in their origins and characteristics, both transitional periods and long-term disruptions share several attributes, especially in terms of their effects on travel behavior as well as travelers’ needs and perceptions. They both impact travelers for an extended period, which can lead to them developing new habits and attitudes to adapt to such changes. Therefore, both transitional periods and long-term disruptions that resulted from transit system construction and repairs, infrastructure failure, and labor strikes were included in this study.

In this study, the term “transitional periods” refers to any planned changes in the transit system that alter the service’s structure and quality and require an extended period of disruption of regular service operations to implement, such as the construction of new transit infrastructure or the substantial upgrade of such infrastructure. After these periods, users expect to have improved transit service quality or options (Fig.  1 ), which may have an impact on their travel behavior and perception. It should be noted that not all infrastructure-related disruptions should be considered transitional periods, as some projects may not improve service afterwards. For example, maintenance-related projects can lead to similar levels of service.

Conceptual framework

The term “long-term disruptions” was used to refer to any long-term transit system disruptions in which transit returns to its initial service configuration after the disruption, with no to minor changes to the service. For both types of disruptions, transit agencies and cities implement a wide array of mitigation strategies. Therefore, this study aims at achieving the following three goals: comprehending the current state of knowledge in the academic literature regarding the impacts of long-term transit system disruptions and transitional periods on travel behavior, travelers’ perceptions and travel needs; understanding the applied mitigation strategies and technologies used to address any undesirable impacts of these disruptions; and synthesizing the findings to identify areas of overlap between studies and prominent gaps in the current state of knowledge. Exploring these issues together informs transit planners and practitioners of lessons learned across studies regarding similarities and differences in terms of impacts, thereby guiding their future practice.

2 Research context

A considerable number of academic studies explored the factors affecting travel behavior and ridership at the city, route, and stop level during regular operational periods of the transit service. Several studies provided a systematic literature review of these factors’ impacts on travel behavior and ridership [ 3 , 4 ]. Nevertheless, there are numerous types of disruptions that can affect the normal operations of the transit network. There are also various classifications for these disruptions. Some studies differentiated between them in terms of whether they are planned or unplanned [ 5 , 6 , 7 ], while another categorization can be in terms of duration (long-term or short-term disruption) as was discussed by Kattan, de Barros [ 8 ].

Disruptions can also be divided based on the transport mode or system they affect (like rail transit or road disruptions) or in terms of magnitude—whether these disruptions resulted in closures of the affected transit stations or only caused the redirection of the stations’ lines, for example [ 9 ]. Furthermore, Zhu and Levinson [ 10 ] categorized transport network disruptions based on their causes; this included transit strikes, bridge closures, earthquakes and special events. A considerable number of researchers investigated the impacts of short-term transit system disruptions that last from a few minutes to hours on travel behavior and transit users’ perceptions [ 11 ]. For example, Saxena, Hossein Rashidi [ 12 ] compared how travelers weigh trip attributes differently in the case of either canceled or delayed transit service when choosing a mode of transport. Other studies focused on understanding the impacts of long-term disruptions of the transport network [ 6 , 8 , 10 , 13 , 14 , 15 , 16 , 17 ].

In regard to review papers that focused on transport network disruptions, Shalaby, Li [ 18 ] conducted a systematic review to identify and analyze journal articles that focused on management strategies for short-term rail transit disruptions and modeling approaches. Zhang, Lo [ 19 ] provided a similar review of the academic literature concerning metro system disruption management and substitute bus service, whilst Zhu and Levinson [ 10 ] discussed theoretical and empirical studies that focus on traffic and behavioral impacts of transport network disruptions. To the best of the authors’ knowledge, none of the previous research efforts provided an in-depth systematic review of the contemporary academic literature concerning the impacts of long-term transit system disruptions and transitional periods on travel behavior, travelers’ perceptions and travel needs. To address this gap, this paper focuses on developing a comprehensive systematic review of the literature regarding the topic.

3 Methodology

A comprehensive systematic review of the academic literature was carried out. Systematic literature reviews are a powerful approach to identify and analyze all relevant research on a given topic within certain parameters. The research process followed PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines for systematic reviews [ 20 ]. It was initiated by conducting a scan of a few relevant articles to establish the keyword search syntax that would then be used to conduct an article search on three notable research databases. These databases were the Transport Research International Documentation (TRID), the Web of Science Core Collection and Scopus. TRID is a comprehensive database that includes more than one million records of transport research [ 21 ]. Following this initial review, four different combinations of keyword search syntaxes were generated based, mainly, on the different categories of long-term transit system disruptions within the scope. More specifically, the four themes of the search queries were as follows: construction and maintenance, general disruptions and closures, labor disputes and strikes, and a more general search related to transport system upgrades or improvements (Table  1 ). It should be noted that the database search queries pertaining to the fourth keyword category were developed and carried out at a later stage to further expand the limited pool of relevant articles found.

Using EndNote, research records for all the documents, which included the abstracts, were organized and some duplicate records were removed. Afterwards, the entire list of records was uploaded to the Rayyan web application [ 22 ] where the remaining duplicates were removed and the record screening process was initialized. Rayyan provided a platform for a collaborative work environment for both authors to screen articles, add notes, label articles, and conduct keyword searches. The screening was mainly done by the first author, while checking the undecided articles was done by both authors. To establish clear guidelines to elucidate the process of determining which documents are relevant, inclusion and exclusion criteria were formulated and subsequently followed to filter out the out-of-scope documents (Table  2 ).

The criteria that guided the selection process included that all papers must be in English and must be full peer-reviewed journal articles published no earlier than in 2011. They must also be mainly concerned with the effects of long-term transit system disruptions. There is no clear distinction between short- and long-term disruptions in the literature. Some researchers generally classified short-term disruptions by lasting up to two or three days [ 23 ]. Therefore, and to increase the number of included studies in this literature review, we considered the threshold of 2 days or more for identifying long-term transit service disruption. Moreover, research articles investigating disruptions due to highway construction or road maintenance works or that study long-term disruptions of other transport modes, such as air travel and ferries, were beyond the scope of this review and, as a result, were excluded. Additionally, efforts that investigated the effects of natural disasters, epidemics, and pandemics such as the COVID-19 pandemic were removed from the analysis, as these types of events are not only impacting the transit system, but also impacting all transportation modes and people’s willingness to make trips to different destinations.

Based on the criteria presented, the number of records that had their titles and/or abstracts manually reviewed by the authors and were subsequently excluded was 6,588, while the number of records deemed preliminarily relevant and were then pursued for full text retrieval were 47 articles. The review of the articles was based on reviewing the papers’ titles first, if the paper title is not clear or suspected of inclusion, the abstract was then reviewed. Afterwards, a swift review of the full text was carried out for these 47 articles. As a result, 30 articles were excluded, and 17 were included (end of Phase 1). Phase 2, the final phase of this process, comprised scanning the reference lists of the 17 acquired articles for any new articles, while applying the same inclusion and exclusion criteria. This step led to the procurement of 5 additional articles that required a full-text review. Only 2 were deemed relevant and were included in the finalized list of articles for the systematic review (19 in total). This process is illustrated in Fig.  2 , which was adapted from Page, McKenzie [ 20 ]. Articles that made it to the finalized list were categorized based on the type of disruption that they each discuss. Subsequent to this categorization, a full review of the 19 articles was performed, and the relevant information regarding the different aspects of each paper, such as the issues addressed; the data used; the utilized research methods; and the key findings, was extracted and organized. This was followed by conducting a qualitative analysis of the papers by analyzing the information on individual, categorical, and general scales as well as synthesizing and comparing the findings and other significant features of the articles.

Flow diagram of the systematic review process conducted

In total, 19 articles were found to focus on long-term transit system disruptions and transitional periods. Even though this may seem like an inconsiderable number of articles for a systematic review, other systematic reviews in the field had similar numbers [ 24 , 25 , 26 ]. Of these 19, three focused generally on long-term disruptions. Seven papers discussed construction-related transit disruptions, and nine papers explored the effects of transit labor disputes and strikes. Appendices 1, 2, and 3 depict the results of this systematic review. In the appendices, studies that have modeled the impact of a mitigation strategy or controlled for it in the model, or  have critically discussed the effects of a mitigation strategy were highlighted.

4.1 General disruptions studies

As can be seen in Appendix 1, only three articles focused on general long-term transit service disruptions or included sections that focused on them. One paper used semi-structured interviews to understand the factors influencing the mode shift to car among transit users in the case of a transit service disruption. In this study, long-term disruptions referred to the hypothetical absence of transit for 10 years [ 27 ]. Pnevmatikou, Karlaftis [ 17 ] investigated the impact of a 5-month partial closure of a metro line in Athens, Greece. Lastly, Yap, Nijënstein [ 28 ] analyzed the impacts of four tram line disruptions in The Hague, the Netherlands. These analyzed disruptions lasted 5 and 20 days.

4.1.1 Methods and data

Nguyen-Phuoc, Currie [ 27 ] used a discourse analysis approach to analyze data collected from semi-structured interview responses of 30 transit users in Melbourne. Most of the participants were from an academic institution (i.e., Monash University). Interviews were coupled with brief questionnaires to collect participants’ socioeconomic information (age, income, occupation, car ownership and driving license) and current travel behavior (i.e., last transit trip). In contrast, Pnevmatikou, Karlaftis [ 17 ] adopted nested logit (NL) and multinomial logit (MNL) models to analyze revealed preference (RP) and stated preference (SP) data. The RP survey (1038 responses) examined the impact of a 5-month metro line closure on transport mode choice, which was conducted immediately after the line’s reopening. The SP survey of transit users was web-based and was collected to understand stated preferences towards travel patterns during hypothetical metro closures. In contrast to the previous two studies, Yap, Nijënstein [ 28 ] utilized smart card data obtained from an automated fare collection (AFC) system during disruptions to compare between predicted and realized transit ridership.

4.1.2 Studies key findings

Nguyen-Phuoc, Currie [ 27 ] found that in the long term, only context-specific factors (travel distance, travel time, travel cost, trip destination and flexibility of alternative mode) have an influence on transport mode shift. The postulated reasons were that participants did not perceive any alteration to the individual-specific factors in the future and that the authors focused on the unavailability of transit for an extremely long period (i.e., next ten years). The study indicated that the prolonged absence of transit services is expected to have an impact on land use and individuals in terms of changing their residential or workplace locations, or both. Participants did not consider trip cancellations during the long-term unavailability of the transit service.

Pnevmatikou, Karlaftis [ 17 ] showed that a metro user’s income was an important element in their decision-making process regarding whether to shift to buses or cars during metro service disruptions. Low-income metro users, regardless of car ownership, prefer using buses during metro disruptions. Additionally, during the disruptions, using a car for travel was negatively correlated with having a flexible work schedule. Yap, Nijënstein [ 28 ] indicated that in-vehicle time in the shuttle bus service (i.e., rail replacement buses) was perceived about 1.1 times more negatively compared to the in-vehicle time in the initial tram line, while waiting times for the shuttle bus service were perceived as approximately 1.3 times higher compared to the waiting times for the regular bus and tram services. The paper also indicated that if the prediction model does not account for vehicle capacity, integrating the positive effect of higher bus frequency would only overestimate the level of service provided by the shuttle buses during disruptions.

4.1.3 Section summary

Very few studies focused on long-term transit service disruptions or included sections that centered around long-term disruptions. One of them used a qualitative approach to develop a conceptual model of mode shift to car among transit users. The other two articles used specific case studies of partial closures of the metro and tram system in Athens and The Hague, respectively. There were no studies exploring system-wide (or a large portion of the system’s) long-term disruptions, nor were there studies that explored long-term disruptions within the North American context. All three studies focused primarily on current transit users’ travel behaviors. Nevertheless, other travelers may respond differently to additional costs imposed by increased traffic congestion. Additionally, since these studies explored only two cases of disruptions, future work is needed to include a wider array of disruptions because transit users’ responses will depend on: available travel options; duration, type, and degree of disruptions; and the used mitigation strategies’ effectiveness. The two quantitative studies investigated the impacts of providing shuttle buses and using an existing parallel transit service to mitigate the impacts of tram and metro closures, respectively. However, the effectiveness of other mitigation strategies is yet to be explored.

4.2 Construction studies

As seen in Appendix 2, seven studies explored the impacts of construction-related disruptions. Most of them focused on the impacts of heavy rail systems’ (e.g., metro and rail systems) construction and maintenance, while only two discussed light rail transit (LRT) systems [ 8 , 9 ]. Construction studies are related to the idea of transitional periods, in which people are expected to have improved transit service quality (or options) after these periods. Of the seven papers, 3 focused on the impacts of construction-related transit disruptions on bike-sharing systems usage. The four others investigated the impacts of construction on: travel behavior changes and travelers’ responses to enroute real-time information disseminated through variable message signs (VMS) [ 8 , 13 ], local air quality [ 29 ], and bus performance [ 14 ]. Additionally, only five articles critically discussed or analyzed the impacts of mitigation strategies.

4.2.1 Methods and data

Of the seven studies, five utilized statistical models to investigate construction-related transit disruptions’ effects on travel behavior and air quality. Bike-share system studies used ridership data from fixed docking stations [ 30 ] or from free-floating bike-sharing systems [ 9 ]. Based on bike-share data, these studies explored the impact of metro and LRT closures that lasted from 7 to 25 days in Washington, D.C., USA and Cologne, Germany. They used autoregressive Poisson log-level time series modeling [ 30 ], negative binomial regression [ 9 ] and linear regressions [ 31 ] to analyze ride-share data for periods before, during, and after disruptions, while controlling for a set of variables (weather conditions, season, day, time of day, etc.). One study [ 31 ] did not directly model changes in ridership due to disruptions, but rather used sensitivity analysis to explore the effects of implementing a new $2 single-trip fare (STF) on ridership, which was introduced concurrently with the SafeTrack program’s operations in Washington, D.C. Another study modeled bike-sharing usage from geographical and temporal perspectives [ 9 ].

On the other hand, other papers used participant survey data to understand changes in travel behavior using summary statistics. For example, Kattan, de Barros [ 8 ] used a revealed preference survey (430 responses) collected one year after the West LRT line’s construction in Calgary, Alberta, Canada, had started but before it ended (the construction project’s duration was ~ 3 years). Nevertheless, it did not model travel mode changes but focused on multinomial logit modeling to study travelers’ behavioral responses to VMS information. Zhu, Masud [ 13 ] used descriptive statistics to analyze panel survey data before (318 and 420 responses) and after (74 and 64 responses) two reductions and closures of service. Another study used fixed-effect modeling to understand the impacts of rail transit construction on the air quality index using air quality data from 28 cities in China [ 29 ]. Lastly, Shiqi, Zhengfeng [ 14 ] used fuzzy aggregation and summary statistics to evaluate the bus layout adjustment scheme from passenger and car driver perspectives and investigated passenger volumes at stops.

4.2.2 Studies key findings

Usage of bike-sharing systems generally increased during construction-related transit disruptions but at different levels. For example, Younes, Nasri [ 30 ] reported ridership increases on weekdays during disruption. Once the affected metro stations reopened, bike-share ridership returned to its pre-surge levels, suggesting a limited lasting effect of the studied disruptions. They also suggested the likelihood of travelers using bike-share as a first- and last-mile solution rather than as an alternative to transit. Similarly, Schimohr and Scheiner [ 9 ] reported a reversion to the original bike-share ridership levels once the disruption had ceased. On another note, Kaviti, Venigalla [ 31 ] indicated that implementing a new $2 single-trip fare increased the number of first-time bike-share riders by as much as 79% immediately after its introduction. The introduction of this new fare co-existed with metro service closures. Additionally, there was also a statistically significant increase in the daily ridership of registered members and casual users at docks near metro stations impacted by the metro service closures.

In regard to the other four studies, Kattan, de Barros [ 8 ] stated that the total demand for travel in areas affected by the construction did not decrease, neither were trip departure times rescheduled. Travel behavior changes were mainly route switching, followed by mode shifting, and then by destination changing. Zhu, Masud [ 13 ] indicated that transit users changed modes or destinations instead of departure time during the complete closure of metro stations. They also reported that ~ 20% of respondents did not return to using the metro even after the service’s full restoration. However, it is not known whether these mode changes are temporary or permanent. Additionally, they observed that wealthier riders are more likely to drive or switch to for-hire options (e.g., Uber and Lyft). On another note, Sun, Zhang [ 29 ] found that rail construction has a greater impact on improving air quality than urban road reconstruction, while Shiqi, Zhengfeng [ 14 ] suggested that factors attributed to transit service and traffic were degraded when bus routing schemes were implemented during disruptions.

4.2.3 Section summary

Few studies in the literature focus on long-term disruptions caused by transit construction or maintenance projects. Three of the seven studies focused exclusively on understanding the disruptions’ impacts on bike-share ridership rather than their effects on using active transportation modes and cycling behavior. Only two articles employed traveler surveys to gain a better picture of people’s travel behavior instead of their tendency to use one specific mode (bike-share) during such disruptions. Moreover, none modeled transport mode changes due to transit system construction projects, but they rather used descriptive statistics to provide information regarding, for example, route and mode changes, while indicating limited trip cancellations or changes in trip departure times.

Additionally, very few studies looked into long-term changes in travel behavior or home and work location decisions influenced by long-term disruptions as Nguyen-Phuoc, Currie [ 27 ] discussed. Most studies focused on immediate impacts and accounted for disruptions within limited time frames. Only five studies explored or modeled the impacts of mitigation strategies on travelers’ travel behaviors or perceptions (Appendix 2). Similarly, it was rare to find articles utilizing detailed mitigation strategy data (e.g., shuttle buses and travel information communications) and travelers’ data in combination with disruption data to explore the mitigation strategies’ effectiveness during transit construction projects. Furthermore, none of the studies were concerned with the relative impact of bus rapid transit (BRT) system construction projects; most of them focused on LRT and metro service construction.

4.3 Labor dispute and strike studies

Only nine papers focused on labor disputes and strikes (Appendix 3). Four of them discussed the impacts of transit operators’ strikes on air quality [ 32 , 33 , 34 , 35 ]. Three focused on transit service strikes’ effects on traffic conditions, while one article investigated the strikes’ impacts on the usage of bike-sharing systems. The remaining paper explored a strike’s effect on undergraduate students’ travel choices.

4.3.1 Methods and data

Of the nine articles, six utilized statistical models to investigate transit labor disputes’ effects on people’s travel behavior and on air quality. Regarding air quality studies, they used pollutant levels as proxies to investigate people’s shifting from transit to using private vehicles. Using air quality monitoring stations data, most of them used case studies that lasted from 3 days [ 32 ] to 51 days [ 33 , 34 ]. Additionally, two used a 2013 strike that occurred in Ottawa as their case study, and only one used a sample of more than one long-term strike for investigating their impacts on air quality [ 35 ]. The most commonly used data analysis methods included regression, difference-in-difference models [ 34 , 35 ], and summary statistics [ 33 ].

On the other hand, three studies explored transit strikes’ effects on traffic conditions using freeways and highways’ loop detector data [ 36 , 37 , 38 ]. These studies used different indicators to understand changes in traffic conditions such as changes in average delay, traffic flow, mean speed, and travel time. The used methodological approaches include summary statistics and developing regression and generalized linear models [ 36 , 37 ]. Only one study [ 39 ] used statistical modeling to isolate strikes’ impacts on bike-sharing system usage; it analyzed the impact of one strike that lasted 7 days in Philadelphia, Pennsylvania, USA, using interrupted time series models. Additionally, only one study [ 40 ] explored strikes’ impacts on transit users and non-users’ travel behavior using surveys and mobile phone app (called iEpi) data. Using four weeks of data, comprising two weeks during the strike and two weeks of normal operation after the strike ended, they developed descriptive statistics to understand changes in walking distance, trips frequency, and visited locations.

4.3.2 Studies key findings

Most of the air quality studies showed substantial increases in fine particulate matter (PM) concentrations during strikes, particularly in busy urban areas. Moreover, some studies indicated large increases in O 3 and CO concentrations. These impacts were mainly attributed to travel behavioral changes; transit users shifted to using private cars. In contrast, two articles reported reductions in NO concentrations during strikes. NO is a gas that is mainly produced by diesel engines, which can be found in public transit buses. Interestingly, one article suggested that PM and O 3 concentrations significantly decreased in the strike’s final 3 weeks. This was attributed to travel behavioral changes; travelers started using more environmentally friendly transport modes as they adapted to the transit service’s absence.

Regarding traffic studies, Anderson [ 37 ] reported an about 47% increase in highway delays during a 35-day strike in Los Angeles, California, USA. More delays were observed along freeways with parallel transit lines that are characterized by heavy ridership. Other researchers made the same spatial observation [ 38 ]. Furthermore, Spyropoulou [ 36 ], using a case study from Athens, Greece, of several strikes lasting between 1 and 5 days, reported similar results. Spyropoulou [ 36 ] stated that strikes increased congestions by increasing traffic flow (up to 30%), reducing mean speed (up to 27%) and increasing travel times (up to 25%).

Strikes also had significant impacts on using active transportation modes. Fuller, Luan [ 39 ] reported a 57% increase in bike-sharing system usage by members and non-members during the 7-day transit operators’ strike. However, bike-share usage quickly returned to previous trends directly after the strike. Additionally, some results suggest that non-members might have used bike-sharing for a slightly longer period. In contrast to previous studies that analyzed the usage of one mode during the strikes (i.e., car or bike-share system), Stanley, Bell [ 40 ] focused on the overall changes in the travel behavior of transit and non-transit users during a longer strike that lasted for more than 30 days. They indicated that transit users visited fewer places and walked more during the 30-day strike.

4.3.3 Section summary

Traffic studies showed that the impacts on the transport network were not equal; this is usually not captured by studies that used aggregate air quality data from fixed monitoring stations. Most of the studies examined changes in using one mode, namely cars or bike-sharing systems. However, only very few studies explored and modeled overall alterations in travel behavior. Moreover, most of the articles used passive data sources from traffic loop detectors, air quality stations, or a bike-sharing system at the aggregate level; this does not offer insights into individuals’ behavioral changes in terms of route choice, departure time, travel perception and overall experience. In fact, none of the studies relied on using social surveys to investigate the short- and long-term impacts of transit operators’ strikes on users. In other words, none of them explicitly focused on understanding changes in transit users’ perceptions and needs. Instead, studies tried to draw conclusions regarding transit users’ and non-transit users’ travel behavior.

Only one study utilized mobile-phone data to explore changes in travelers’ behaviors in more detail. This calls for more investigation into possibly using such tools in obtaining larger and more representative samples that can be combined with surveys to better understand different aspects of travelers’ decision-making behaviors during transit operators’ strikes. Furthermore, none of the reviewed studies explored the impacts of service strikes and information availability on travelers’ perceptions using data collected from social media platforms such as Twitter, for example. Table 3 shows an aggregated summary of the analyzed papers from the three categories (general causes, construction-related, and labor-related disruptions) and their different aspects including users’ perceptions and travel behaviors that were investigated.

4.4 Mitigation strategies

Several mitigation strategies were discussed in the reviewed literature. They generally fall under three broad categories: backup transport services, policy-based measures, and impact assessments (Table  4 ). In the table, articles are also sorted by the disruption type that they are associated with. Of the 19 papers chosen for this review, 10 articles discussed disruption mitigation strategies in some form.

Backup transport services are mitigative actions where some alternative form(s) of transport is provided during disruptions to regular transit services. They can be considered to be a form of policy-based measures; however, a distinction has been made between the two since not all of the policy-based measures discussed in the articles were backup transport services. Several articles discussed the level of backup transport services and their impact. For example, Kattan, de Barros [ 8 ] discussed the benefits of implementing a temporary BRT service, which followed an alignment similar to that of the LRT under construction, as a proactive mitigation measure that encouraged travelers to shift to using transit. Yap, Nijënstein [ 28 ] found that people overestimated the in-vehicle and waiting times associated with using bridging buses compared to their in-vehicle and waiting times using the initial tram service. On another note, Schimohr and Scheiner [ 9 ] indicated that travelers’ proximity to stations with substitute or redirected lines was associated with a decrease in the number of bike-sharing trips, suggesting that people used transit at these locations more than they used the bike-share system during service disruption. Nevertheless, most of the studies that discuss this point agree that bus bridging involves a higher level of inconvenience for users, thereby encouraging them to change modes or destinations.

The second category is policy-based measures. This strategy includes providing and improving communications and the dissemination of information to travelers through delivering consistent updates regarding the disrupted transit services, traffic conditions, available alternative modes of transport, etc. It could also include reduced fares, for using transit or a form of active transportation for example, to promote using sustainable transport modes during the disruption to alleviate the hike in traffic congestion. The reviewed articles discussed or analyzed several policy-related amendments or measures. They include introducing a single-trip fare option to encourage riders to use the bike-sharing system and using improved communications methods to disseminate information; those approaches were studied by Kaviti, Venigalla [ 31 ] and Kattan, de Barros [ 8 ], respectively. In addition, Anderson [ 37 ] reported that an additional transit service was contracted (i.e., the Red Line Special bus service) to duplicate part of a closed metro route; this could also be considered a backup transport service. Similarly, Moylan, Foti [ 38 ] indicated that during the Bay Area Rapid Transit (BART) service shutdown, a local bus agency (i.e., AC Transit) increased frequencies on Transbay bus service routes. However, the benefits of policies like contracting new services or increasing transit services offered by other agencies were not explicitly measured in previous efforts. Regarding the third category, only one paper [ 14 ] focused on evaluating a metro construction project’s disruptive effects on bus performance in the city of Ningbo, China.

5 Discussions and policy implications

The results of this study demonstrate that there is generally a lack of academic research concerning long-term transit service disruptions and transitional periods. Nevertheless, the majority of the identified academic papers are relatively recent and were published during the past five years. This may suggest that this key topic has been gaining more traction in recent years. This showcases this topic’s relevance and the possibility of having more efforts in this area soon. This is in alignment with the increase in worldwide governmental funding opportunities to develop new transit infrastructure to foster economic growth and face climate change. For example, Canada’s federal government revealed a new sizeable funding of $14.9 B for new public transit infrastructure in February 2020 [ 41 ]. Similar efforts dedicated to providing more funding for building and upgrading public transport can be found in Europe, the US and China [ 44 , 45 , 46 ]

According to the number of identified documents, there is a wide agreement and overlap in the reviewed literature regarding the negative impacts such disruptions and transitional periods have on travelers and also regarding the importance of using a range of mitigation strategies. The most common impacts are mode changes. Very few studies indicated other types of changes such as route changes, trip departure time changes, and destination changes. Some evidence, which is rather limited, shows that transit users did return to their previous travel behavior after the end of long-term service disruptions. Nevertheless, it is not clear if these changes are temporary or permanent. Other studies indicated that bike-share systems ridership increased during disruptions. However, these ridership levels returned to their pre-disruption levels after the reopening of the transit service, suggesting a limited lasting effect of long-term disruptions on people’s mode choice to continue using the bike-sharing systems. Providing new backup transit services and rerouting and enhancing parallel services were the most common mitigation approaches widely discussed in the literature to deal with long-term transit disruptions. Previous efforts showed good use of passive data sources from air quality monitoring stations, highway loop detectors, bike-share system counters, and automated fare collection systems to establish evidence of the negative effects of such periods.

Despite these efforts in the literature, travelers’ perceptions and needs during these periods are minimally addressed or analyzed. Additionally, it was rare to find studies that explicitly incorporated or controlled for the expected impacts of the transit projects after their completion. In other words, transitional periods may have more positive outcomes on transit users’ perceptions and travel behaviors after the project is finalized, due to enhanced service quality for instance, compared to other long-term disruptions. Such effects were underexplored in the literature.

The academic literature on long-term disruptions and transitional periods is currently quite divorced from the practice. For example, there is a dearth of studies that seek to derive lessons from past and current practices to help advance the practice of using effective mitigation strategies in different contexts and for different purposes. Additionally, a considerable number of the articles focused solely on understanding the impacts of long-term service disruptions on the usage of one transport mode, such as bike-sharing system usage, or one element, such as air quality or traffic conditions, rather than drawing a complete picture of people’s decision-making process and changes in their travel behaviors and needs. It was also rare to find studies that used a statistical model to better understand travelers’ behaviors during and/or following different types of long-term disruptions and transitional periods.

Most of the studies focused on measuring the short-term impacts of transit service disruptions. This may be related to the fact that most of the analyzed disruptions in the academic literature lasted for a few days or weeks. Nevertheless, articles exploring both short- and long-term impacts of longer transit service disruptions and transitional periods that last for a few months or even years were very limited. In fact, only two studies focused on exploring the impacts of longer disruptions that lasted more than a few months. Using surveys, one study regarding disruptions in Athens explored the immediate impact of a 5-month disruption on travel behaviors, while another study from Calgary explored the 1-year impact of an LRT system construction project, which lasted for about 3 years. Therefore, it is challenging, based on the limited research available, to understand the changes in travel behavior during these prolonged periods and to understand whether these long-term disruptions have an extended or permanent impact on travelers’ behaviors. Potential changes that may not be considered in shorter disruptions include relocation and/or reductions in travel demand because of moving closer to work or school, changing jobs, joining a ride-sharing program, and increasing telecommuting. Some of the key policy recommendations of this research are listed below.

With the need for academic studies that focus on the short- and long-term impacts of different long-term disruptions and transitional periods, cities and transit agencies are encouraged to work with the academic community to test different sets of mitigation strategies in different contexts, scenarios, and at different scales. These studies should also include information about changes in travelers’ behaviors, perceptions, and well-being in order to evaluate the used mitigation strategies and their relative impacts, which would inform future policy making.

With the emergence of more academic studies, as well as non-academic reports, in this area, lessons from the literature and practice should be organized and used in more systematic ways to assist in developing a policy guide to help in managing these disruptions. This will aid in guiding future practices that should aim to maintain higher levels of the transit services’ attractiveness during such periods for both transit and non-transit users. The prospect of providing adequate active transport alternatives that would encourage people to shift to using active transportation modes should also be explored. This could potentially reduce the stress on the public transportation and road networks.

Using agreements with private bus operators, ride-hailing services, bike shops, advocacy groups, and bike-sharing and scooter-sharing companies, cities can help reduce the impact of such periods on travelers. As seen in the literature, offering bike-sharing services and making them cheaper or more accessible by offering more payment options during long-term transit service disruptions can work as a mitigation strategy. This could be coupled with looking beyond the physical availability of alternative modes by testing different pricing scenarios to provide transport alternative(s).

Research suggests that using greener transport options may be adopted more widely by travelers if adequate policies were in place during such disruptions. This would capitalize on the increased flexibility of travelers to try out new transport modes during such periods. This might help in increasing cities’ shares of active transportation if such mode changes could be sustained after the disruption and adopted permanently by travelers. Nevertheless, currently, there is limited evidence that this is the case.

People will not benefit or suffer increases in their monetary and non-monetary costs equally because of any long-term transit system disruptions or transitional periods. Therefore, transit agencies should assess the equity impacts of such extended time periods on different groups of travelers. This will be context-specific and will help in articulating more sensitive policies that match different groups of users’ needs.

Finally, it was reported in the literature that the provision of alternative public transport options with a high transit service level coupled with the efficient dissemination of pre-trip and enroute, real-time travel information (e.g., updates on traffic and on areas affected by the disruption) resulted in an increase in transit use during the disruption. Moreover, evidence of the importance of using social media, graphics, and short videos in communicating information during the COVID-19 pandemic was discussed in the literature [ 47 ]. Learning from these lessons, more understanding of the importance of efficient and timely dissemination of information plans using social media or other platforms is essential. This is to help cities in informing people about expected impacts and options, which can help in alleviating stress on transit segments.

6 Conclusions

This study aimed to explore the current state of knowledge concerning transit systems’ transitional periods and long-term disruptions and to understand the actively used disruption mitigation strategies and technologies that are implemented to address or alleviate any of their undesirable impacts on travelers. To achieve these goals, a comprehensive systematic review of the academic literature was conducted. In total, 19 peer-reviewed journal articles were identified and analyzed. This systematic review helps identify the major knowledge gaps in the literature. The results of this study demonstrate that there is generally a lack of academic research works concerning long-term transit service disruptions and transitional periods. In fact, travelers’ perceptions, travel behaviors and changing needs during these disruptive periods were minimally addressed or analyzed. Key conclusions and recommendations are discussed below.

Given the range of different types of long-term transit system disruptions (e.g., construction, labor disputes and service failures); various disruption time frames (from a few days to several years); varying spatial coverage (from one line to system level); and different disrupted modes (e.g., bus, metro and tram), much more work can be done to explore the effects of such disruptions on people’s travel behavior and perceptions.

The possible impact of long-term disruptions on travelers in terms of changing modes, routes, trip departure times, frequency of trips, destinations, and work and home locations in addition to increasing telecommuting and trip sharing are widely recognized in the literature. However, studies rarely explored explicitly the factors affecting changes in travel behavior like shifting to different routes or changing the frequency of trips or the factors influencing relocation for transit and non-transit users using statistical models. This can be an important area for future work.

The relative importance and impact of disruption mitigation measures, while understanding how these measures could work together, within the context of long-term disruptions are rarely investigated in the literature. In fact, the current academic literature provides transit agencies with very limited information to assist them. Such knowledge can inform the processes of planning for long-term disruptions to implement more efficient and effective strategies.

Most of the studies were quantitative in nature and provided some relevant findings; however, qualitative studies can provide in-depth insights into the intersection between how, why, who, and what questions that are related to different types of disruptions. For example, it can help in understanding the importance of using different mitigation strategies for different groups of the population and their relation to different types of disruptions. Therefore, future research can focus on using qualitative approaches to elicit information not only from transit and non-transit users, but also from transit agencies and operators to understand their perspectives.

The reviewed literature generally used data from two main sources: from traveler surveys and from passive data sources that are obtained from air quality monitoring stations, bike-share systems, and highway loop detectors. Therefore, using emerging data sources such as cellular phone data and mobile app data can be explored for future studies to give a better understanding of the different long-term disruptions’ impacts. Social media data, farebox system data, and web surveys can be also incorporated in these studies.

Several studies used summary statistics, difference-in-difference approaches, or a dummy variable to isolate the impacts of long-term disruptions on different aspects (e.g., air quality, traffic conditions, and bike-share usage). However, these studies ignore that a long-term disruption entails an extended period of time, which can see different movement patterns within this period as indicated by Chandler and Shymko [ 34 ]. They stated that relying only on short-term results to draw conclusions regarding long-term impacts of long-term disruptions can lead to an overestimation of the negative effects. Therefore, future research could look into different patterns within such time frames.

Similarly, temporal changes in travel behavior after long-term disruptions or transitional periods end are rarely explored in the literature, particularly for longer disruptions that last for more than a few weeks. Some authors indicated that transit ridership can take several weeks to reach pre-disruption levels [ 37 ]. Therefore, exploring changes occurring over time to travelers and, more specifically, transit users’ travel behavior could be a viable future research endeavor.

Previous studies explored the impacts of long-term disruptions and transitional periods on bike-share usage; however, the academic literature is lacking in studies that investigate their impacts on using other active transportation modes, such as walking and cycling. Since these trips, particularly walking trips, are usually underreported in travel surveys, using sensors data from mobile phone apps can be beneficial to understand changes before, during, and after long-term disruptions for different groups of travelers.

It was found that very few articles explored changes in travelers’ perceptions, satisfaction, and needs due to transitional periods in comparison with long-term transit system disruptions triggered by other causes. Transitional periods, which usually lead to different outcomes in terms of improved service quality after ending compared to other long-term disruption periods, were not explicitly explored in the literature. Transitional periods’ ultimate positive outcomes on users’ perceptions and travel behaviors could be a viable focal point for future research efforts.

Incorporating social issues, such as equity concerns, and seeking to derive lessons to help understand the equity impacts of long-term disruptions and transitional periods on different groups of populations are yet to be accomplished. These groups can include Indigenous populations, visible minorities, and people with systemic barriers to using other transportation modes. Additionally, there is a lack of research to both understand and address the sociopolitical, institutional and community capacity dimensions, which is an important aspect during such periods.

Finally, this study aimed to derive lessons from the current academic literature on the effects of transit systems’ long-term disruptions and transitional periods. Exploration of this rather diverse research area will not only inform professionals but will also highlight important gaps in the current literature for researchers. Future research can expand the presented efforts and focus on reviewing transit agency reports and studies and conducting surveys and interviews with transit planners to record their experience and to better understand their perspective of the effects of transit systems’ long-term disruptions and transitional periods. This is to help cities and transit agencies to better anticipate and manage “change”. This will, in turn, help to facilitate and secure the development of their public transport networks while planning and being better prepared for long-term transit system disruptions, thereby aiding them in achieving their overarching sustainability goals.

Data availability

No datasets were generated or analysed during the current study.

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We would like to thank the Social Sciences and Humanities Research Council (SSHRC) of Canada and Infrastructure Canada (INFC) for partially funding this research.

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The authors confirm contribution to the paper as follows: study conception and design: Noureldin & Diab; data collection: Noureldin; analysis and interpretation of results: Noureldin & Diab; draft manuscript preparation: Noureldin & Diab. All authors reviewed the results and approved the final version of the manuscript.

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1.1 General disruptions studies

• Rows 2 and 3 include a study that has modeled a mitigation strategy’s impact. Automated fare collection (AFC). Stated preference (SP). Revealed preference (RP). Multinomial Logit Model (MNL). Nested logit (NL). “Y” refers to the model’s dependent variable(s). “X” refers to the model’s independent variables

2.1 Construction studies

• Rows 1, 3, and 7 include a study that has modeled the impact of a mitigation strategy. Rows 4 and 6 include a study that has discussed or investigated the impact of a mitigation strategy using summary statistics. “Y” refers to the model’s dependent variable(s). “X” refers to the model’s independent variables. Stated preference (SP). Revealed preference (RP). Sulfur dioxide (SO 2 ). Nitrogen dioxide (NO 2 ). Fine particulate matter smaller than or equal to 10 µm in diameter (PM 10 ). Fine particulate matter smaller than or equal to 2.5 µm in diameter (PM 2.5 ). Gross domestic product (GDP). Analysis of variance (ANOVA). Variable message signs (VMS). Light rail transit (LRT)

3.1 Labor dispute and strike studies

• Row 9 includes a study that has modeled the impact of a mitigation strategy. Rows 5 and 6 include a study that has discussed or investigated the impact of a mitigation strategy using summary statistics. “Y” refers to the model’s dependent variable(s). “X” refers to the model’s independent variables. Fine particulate matter smaller than or equal to 10 μm in diameter (PM 10 ). Fine particulate matter smaller than or equal to 2.5 μm in diameter (PM 2.5 ). Sulphur dioxide (SO 2 ). Ozone (O 3 ). Nitrogen oxide (NO or NO X ). Carbon monoxide (CO). Condition probability function (CPF). Bay Area Rapid Transit (BART). Los Angeles County Metropolitan Transportation Authority (MTA)

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Noureldin, M.G., Diab, E. Impacts of long-term transit system disruptions and transitional periods on travelers: a systematic review. Discov Cities 1 , 15 (2024). https://doi.org/10.1007/s44327-024-00015-5

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Received : 05 March 2024

Accepted : 14 August 2024

Published : 27 August 2024

DOI : https://doi.org/10.1007/s44327-024-00015-5

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