The National Academies

NCHRP 03-139 [Active]

Next Generation of the USLIMITS2 Speed Limit Setting Expert System

  Project Data
Funds: $450,000
Staff Responsibility: Camille Crichton-Sumners
Research Agency: The University of North Carolina at Chapel Hill
Principal Investigator: Raghavan Srinivasan
Effective Date: 8/1/2020
Completion Date: 7/31/2024
Comments: Research in progress.



NCHRP Research Results Digest 318: An Expert System for Recommending Speed Limits in Speed Zones (2006) resulted in the deployment of the USLIMITS2. USLIMITS2, hosted by the Federal Highway Administration, employs a decision algorithm to advise the user of the recommended speed limit for the specific road section of interest. The existing algorithm focuses primarily on operating speeds (85th percentile speed, 50th percentile speed) and other variables entered by the user to determine the recommended speed limit. USLIMITS2 was updated in early 2018 to improve usability, but the decision algorithm has not been updated since 2006. New research should refine the decision rules of the algorithm and develop the next generation of USLIMITS2.




The objectives of this research are to (1) determine what updates are needed for the USLIMITS2 decision algorithm to establish safe, credible, and enforceable speed limits for a variety of facility types and contexts, including high, moderate, and low speed facilities that serve all roadway users; (2) update the algorithm and conduct user testing; (3) identify and incorporate potential enhancements that will increase the user base; and (4) develop an implementation and training plan.






Task 1.  Conduct a literature review to (1) identify and analyze algorithms within relevant existing decision support systems (DSS) to determine the data requirements, outputs, and DSS user experience; (2) assess the state of practice within the United States, including a review of guidelines, criteria, and procedures used for setting speed limits; and (3) identify ongoing and recently completed studies and summarize available research tools and guidance.


Note. Findings from recent studies and surveys should be used to avoid duplication of effort.


Task 2. Conduct a comprehensive review of the current USLIMITS2 program, algorithms, data sets, and other available resources. Consider other data inputs identified in Task 1.  Identify end-user challenges and implementation barriers encountered by state and local transportation agencies.


Task 3. Prepare an interim report that documents the work completed in Tasks 1, 2, and 3. Include a detailed work plan for the work anticipated in Phase II. Include an anticipated list of subject matter experts versed in setting and enforcing speed limits that will be involved in subsequent tasks.




Task 4. Develop a framework, acceptance processes, and new or updated decision rules in consultation with the approved subject-matter panel.


Task 5. Prepare an updated work plan to incorporate Task 5 results and software implementation options.


Note: Participate in an in-person NCHRP project panel meeting to discuss Task 1 through 6. TRB will cover the costs associated with meetings at TRB facilities, teleconference services, and any approved NCHRP panel travel.


Task 6. Implement the work plan. Develop software to apply the updated algorithms and make necessary updates to the interface (i.e., adding new input fields, updating existing input fields, and modifying output reports).


Task 7. Prepare a Draft User Manual for USLIMITS3 and conduct beta testing of the updated system with both the subject-matter experts and an independent group of representative users.


Task 8. Prepare a technical report documenting the work completed in Tasks 5 through 8. Include a detailed work plan for the work anticipated in Phase III.


Task 9. Host a virtual panel demonstration for the panel.




Task 10. Update the system and finalize the user manual as necessary based on beta testing findings and complete final testing to ensure the system works as intended.


Task 11. Conduct a virtual demonstration for user acceptance.


Task 12. Prepare the updated files and work with FHWA to implement the program on the FHWA’s server.


Task 13. Prepare a maintenance guide for the website administrator, documenting the changes made to the algorithms and any information necessary for future maintenance of the system.


Task 14. Develop an implementation, marketing, outreach, and training plan.


Task 15. Prepare final deliverables that fulfill the research objectives and document the entire research effort. The final deliverables will also include an executive summary, a stand-alone guidance, recommendations for prioritized research needs, and outreach and presentation materials.

To create a link to this page, use this URL: http://apps.trb.org/cmsfeed/TRBNetProjectDisplay.asp?ProjectID=4736