A literature search is conducted in six steps:
Highlights from each of these steps are presented in this section. For a more detailed discussion of each step, review the "Literature Searches: How to Search" section of Transportation Research E-Circular 194: Literature Searches and Literature Reviews for Transportation Research Projects.
Step 1: Define the Search Topic and Scope
To refine the research idea or need for the search, consider the following:
Step 2. Choose the Resources to Search
Check several resources in your search, including:
See the Resources: Where to Search section of this guide for additional resources and information.
Note: Not all resources are publicly available or online. Librarians, especially those who specialize in the transportation field, are the best source of information about new databases or changes to existing databases. University, corporate or public librarians may have access to subscription databases and other sources that can provide resources free of charge or at a reduced cost.
TRID provides access to more than 1.3 million transportation research records worldwide. It includes records from TRB’s Transportation Research Information Services Database, the OECD’s Joint Transport Research Centre’s International Transport Research Documentation (ITRD) Database and the Research in Progress (RiP) Database.
Links to recently published records, recently added records, advanced search features, search history, site help, rich site summary (RSS) feeds, recent records by mode, hot topics and recent TRB publications are availilable from the TRID homepage.
Google Scholar, a subset of the Google internet search engine, provides access to scholarly literature across many disciplines. Sources include publications from academic publishers, professional societies, digital repositories and universities, and case law.
Searching Google Scholar
The Scholar Settings feature allows searchers to choose the display language, choose the languages of the results, make results open in a new window, specify the citation manager for exporting links and set the Library Links feature to show library access links for up to five libraries.
Step 3. Choose Search Terms
To develop the initial search term list, use the words that describe the search topic developed in Step 1. Then:
The Transportation Research Thesaurus (see below) is a valuable tool for identifying search terms.
Note: When creating the list of search terms, keep in mind that acronyms can have different meanings for different audiences; words with diacritics (the marks above or below characters) may need to be searched separately (with and without the diacritic); and terminology may vary from country to country (e.g., truck vs. lorry).
The TRT is an online resource of standardized vocabulary that allows users to index, search and retrieve technical reports, research documents and other transportation information in the Transportation Research Information Services (TRIS) Database. Keywords provided in the TRT represent all modes and aspects of transportation—from construction, maintenance and materials to economic and social factors. With more than 9,500 terms, this free resource provides references to related words and concepts, improving information access to the transportation community.
The following resources provide information about the TRT:
Step 4. Compile the Search Strategy and Run the Search
Begin the search process at the help pages of the database, search engine or catalog that you are using to understand how searches work in that resource. Reading this information could save you a tremendous amount of time.
Then develop a search strategy that explores how terms are linked instead of simply adding any potential words into a single search field. Below are a few basic strategies for using keywords and search terms.
And, Or, Not (Boolean Operators)
Most databases and search engines support Boolean logic, allows users to broaden or restrict a search. Boolean functionality lets users:
Advanced Search Tips
Most databases and library catalogs offer advanced search functions. Below are some of the most common advanced search options:
Step 5. Review the Search Results
After running the initial search, review the results to determine if more searching is necessary and if the search strategy needs modification.
Looking Beyond Online Resources
Knowing When to Stop
Knowing when to stop is subjective and is often based on time constraints. It's unrealistic to expect to find 100% of relevant research on a topic, regardless of the amount of time spent. An initial, focused effort of 3 to 5 hours of proper searching may yield 80% of all relevant citations that can reasonably be located using sound techniques in the proper sources. Spending another 10 to 20 hours may only yield 5% to 10% more relevant citations. Some citations may never be found due to indexing errors, timing and other variables. Consider whether continuing the search is producing new, relevant citations.
Step 6. Organize the Results
Record full bibliographic information (title, author, year of publication, journal title, volume number) and notes about the content (e.g., the database used to locate the resources, libraries that might house the resources) of each relevant citation. For extensive or ongoing searches, consider using a bibliographic management tool to organize the results and retrieved items. Bibliographic management software allows users to create a personal database of references to keep track of all citations—books, book chapters, journal articles, dissertations, recordings, webpages, letters, manuscripts and many other types of documents.
RSS Subscriptions and Alerts
TRID and other databases allow users to share and organize search results using tools and social networking options directly from the search interface. They may also offer subscriptions to RSS feeds and alerts. RSS feeds automatically download updated information that meets search criteria to the user’s computer; alerts email updates of the latest relevant results to the researcher. These and other tools allow searchers to continue accessing the latest research on a topic long after they have completed the initial search.
Finding a Full-Text Document
Some databases provide links to the full text of a document or provide selective links. The full text may also be available through local or university library catalogs, e-journals with subscriptions, WorldCat, interlibrary loans and document delivery services, and direct contact with authors, publishers and sponsoring agencies.
Practical Tips From Transportation Librarians
6 Steps to an Effective Literature Search, London School of Hygiene and Tropical Medicine.
Basic Search Tips and Advanced Boolean Explained, J. Barker, University of California, Berkeley, 2007.
"Before You Search the Literature: How to Prepare and Get the Most Out of Citation Databases,", J. M. McGrath, R. E. Brown and H. A. Samra, Newborn and Infant Nursing Reviews, Vol. 12, No. 3, September 2012, pages 162–170.
Conducting a Literature Search for Research Projects, Z. K. Keppler and V. Fout, Ohio Department of Transportation, August 2, 2012.
How to Conduct a Literature Review, J. Mattson and D. Ripplinger, presented at the Small Urban and Rural Transit Center Transportation and Logistics Seminar, December 1, 2008.
An Introduction to Information Literacy, Northwestern University Transportation Library, Northwestern University Traffic Institute, School of Police Staff and Command, undated.
Library Orientation for Offsite Students, Northwestern University Transportation Library, Northwestern University Traffic Institute, School of Police Staff and Command, undated.
Moving Beyond Google: Why and When to Go Pro, M. E. Bates, white paper created for ProQuest, 2014.
Steps for Conducting a Literature Review, University of West Florida Libraries, undated.
Tips for Conducting a Literature Search, AlphaPlus Centre, April 2004.