Considering Roadway Context in Setting Posted Speed Limits

The National Cooperative Highway Research Program (NCHRP) Project 17-76 investigated factors that influence operating speed and safety through a review of the literature and an analysis of the relationships for speed, safety, and roadway characteristics on urban/suburban streets. That knowledge, along with a review of existing speed limit setting practices, was used to develop a Speed Limit Setting Procedure (SLS-Procedure) as well as a user manual to explain the SLS-Procedure. In addition, the SLS-Procedure was automated via a spreadsheet-based Speed Limit Setting Tool (SLS-Tool). These products will permit engineers to make informed decisions about the setting of speed limits. The SLS-Procedure is fact based and transparent, relying on a set of decision rules that consider both driver speed choice and safety associated with the roadway. The SLS-Procedure was designed to be applicable across different roadway types and contexts by having a set of unique decision rules for four combinations of roadway types and contexts: limited-access, undeveloped, developed, and full-access facilities. The SLS-Procedure uses the operating speed distribution as a starting point for the suggested speed limit, with the resulting suggested value based on consideration of roadway type, context, safety performance, and other characteristics.

[1]  Douglas W Harwood,et al.  Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects , 2018 .

[2]  K. Fitzpatrick,et al.  Current Attitudes among Transportation Professionals with Respect to the Setting of Posted Speed Limits , 2019, Transportation Research Record: Journal of the Transportation Research Board.

[3]  Nikiforos Stamatiadis,et al.  Developing an Expanded Functional Classification System for More Flexibility in Geometric Design , 2018 .

[4]  Karim El-Basyouny,et al.  Exploring the association between speed and safety: A path analysis approach. , 2016, Accident; analysis and prevention.

[5]  Shlomo Bekhor,et al.  The Relationship between Free-Flow Travel Speeds, Infrastructure Characteristics and Accidents, on Single-Carriageway Roads , 2017 .

[6]  Kay Fitzpatrick,et al.  Development of a Posted Speed Limit Setting Procedure and Tool , 2021 .

[7]  Jessica B Cicchino,et al.  Lowering the speed limit from 30 mph to 25 mph in Boston: effects on vehicle speeds , 2019, Injury Prevention.

[8]  Karin M Bauer,et al.  Evaluation of the 13 Controlling Criteria for Geometric Design , 2014 .

[9]  Brian D. Taylor,et al.  Eighty-Five Percent Solution: Historical Look at Crowdsourcing Speed Limits and the Question of Safety , 2020 .

[10]  Nikiforos Stamatiadis,et al.  An Expanded Functional Classification System for Highways and Streets , 2017 .

[11]  D. Solomon.  Accidents on main rural highways related to speed, driver, and vehicle , 1964 .

[12]  C. Hedges.  SAFETY IMPACTS AND OTHER IMPLICATIONS OF RAISED SPEED LIMITS ON HIGH-SPEED ROADS , 2004 .

[13]  Douglas W Harwood,et al.  A Performance-Based Highway Geometric Design Process , 2016 .