Development of a Posted Speed Limit Setting Procedure and Tool

National Cooperative Highway Research Program (NCHRP) Project 17-76 was tasked with identifying factors that influence a driver’s operating speed and then developing a Speed Limit Setting Procedure (SLS-Procedure) and automating that procedure with a spreadsheet-based Speed Limit Setting Tool (SLS-Tool). The SLS-Procedure and SLS-Tool are used to calculate the suggested speed limit for a segment. The goal of the SLS-Procedure and SLS-Tool is to produce an unbiased and objective suggested speed limit value. Traffic engineers can use the SLS-Procedure and the suggested speed limit generated by the SLS-Tool to communicate with the public or government officials to explain the methodology behind setting speed limits. Chapter 1 of this report provides background information, Chapter 2 discusses the research approach, Chapter 3 presents the findings, and Chapter 4 gives conclusions, recommendations and suggested research. Appendix A presents the findings reported in the research literature on the relationships among traffic crashes, operating speed, and roadway factors, including posted speed limit, for urban and suburban streets. Appendix B discusses the findings reported in the research literature for rural highways and limited-access highways regarding the relationships among crashes, operating speed, and roadway characteristics including posted speed limit. Appendix C presents information on current approaches to setting speed limits including a summary of key publications calling for changes to how speed limits are set. It also provides an overview of various methods being used in the United States and in other countries including introducing recent trends to employ citywide or default speed limits. Existing material and proposed changes to the Manual on Uniform Traffic Control Devices (MUTCD) are summarized. To aid in understanding the relationships between operating speed and posted speed limit, this appendix includes plots showing average speed by posted speed limits. Appendix D identifies the relationships among operating speed, crashes, and roadway characteristics including posted speed limit and vehicle volume for a database of Austin, Texas, sites. Appendix E identifies the relationships among crashes, roadway characteristics, posted speed limit, and vehicle volume for a database of Washtenaw County, Michigan, sites. Appendix F provides an overview of the decision rules selected for the four Speed Limit Setting Groups (SLSGs), which are Limited Access, Undeveloped, Developed, and Full Access. Finally, Appendix G includes the slides and presenter notes used in one of the workshops presented during the project.

• Record URL:
  http://www.trb.org/Main/Blurbs/182154.aspx
• Supplemental Notes:
  • Submitted March 2021.
• Authors:
  • Fitzpatrick, Kay
  • Das, Subasish
  • Pratt, Michael P
  • Dixon, Karen
  • Gates, Tim
• Publication Date: 2021

Language

• English

Media Info

• Media Type: Digital/other
• Edition: Final Report
• Features: Appendices; Figures; References; Tables;
• Pagination: 190p
• Serial:
  • NCHRP Web-Only Document
  • Issue Number: 291
  • Publisher: Transportation Research Board

Subject/Index Terms

• TRT Terms: Automation; Methodology; Speed limits
• Subject Areas: Highways; Operations and Traffic Management; Safety and Human Factors;

Filing Info

• Accession Number: 01773839
• Record Type: Publication
• Report/Paper Numbers: NCHRP Project 17-76
• Files: TRIS, TRB, ATRI
• Created Date: Jun 7 2021 12:52PM