BACKGROUND 

The applicability of the 85^th percentile speed for determining posted speed limits is a complex and controversial issue of concern to state departments of transportation (DOTs). The 85^th percentile is the speed at or below which 85 percent of free-flowing traffic travels. It is sometimes used to provide an indication of the free-flow operating speed on the roadway for determining traffic control device applications. It has been used for decades as the basis for setting speed limits. 

In recent years, calls have been made to eliminate the 85^th percentile speed as the basis for setting speed limits, especially in urban areas. Proponents of the 85^th percentile speed argue that (1) it is a good measure of the speed at which drivers feel safe and comfortable on a given road; (2) it is a relevant data point that can indicate whether other modifications or speed management strategies might be needed to achieve compliance or some level of a self-enforcing road design; (3) and setting speed limits at or near the 85^th percentile speed can reduce speed variance and improve safety. Conversely, critics argue that (1) the 85^th percentile speed is not a reliable measure of safe driving; (2) it can be influenced by many factors, such as traffic volume, road conditions, and drivers’ perception of law enforcement activity; and (3) setting speed limits at or near the 85th percentile speed can encourage drivers to travel at higher speeds. Therefore, critics argue that the 85^th percentile speed should be removed as a factor and that the Safe System approach should be required instead. 

Recent research and reasoning for moving away from the 85^th percentile speed on urban arterials and residential streets do not address speed limits on freeways, expressways, and rural highways. Therefore, research is needed to examine the applicability of the 85^th percentile speed for setting speed limits on freeways, expressways, or rural highways. 

OBJECTIVES 

The objectives of this project are to (1) examine the applicability of the 85^th percentile speed as a factor in setting speed limits on freeways, expressways, and rural highways and (2) prepare a guide for state DOTs and other agencies with the authority to set speed limits on freeways, expressways, and rural highways that includes, at a minimum, implementation considerations, an application framework, and outreach materials for communication with policymakers. 

RESEARCH PLAN 

The work proposed must be divided into tasks and/or phases. Proposers must describe the work proposed in each phase and task in detail. The research plan should build in appropriate checkpoints with the NCHRP project panel, including, at a minimum, (1) a kick-off teleconference meeting to be held within 1 month of the contract’s execution date and (2) one in-person interim deliverable review meeting. An annotated outline for the guide shall be included with the interim report. The draft guide is due no later than 6 months before the contract end date. 

The research plan shall include a workshop with at least 15 diverse representatives of state DOTs to (1) demonstrate the draft guide and (2) collect and use participant feedback to revise and finalize the guide. At a minimum, workshop preparations shall include issuing invitations to NCHRP-approved participants and preparing a final list of attendees; providing travel support for workshop attendees; providing catering services for all participants, including panel members; preparing name tags for all participants; and preparing workshop materials, including PowerPoint presentations and any handouts. 

The final deliverables will include at a minimum: 

1. A guide. 

2. A final report that includes:

•  a summary of the research findings;
•  documentation of the entire project;
•  an executive summary; and
•  recommendations of needs and priorities for additional related research. 

3. A PowerPoint presentation with presenter’s notes summarizing the research findings. 

4. A stand-alone technical memorandum titled “Implementation of Research Findings and Products”. 

STATUS: Proposals have been received in response to the RFP. The project panel will meet to select a contractor to perform the work.