The objective of this research is to recommend an improved Crash Experience Traffic Signal Warrant that is suitable for inclusion in the MUTCD, based on research and consistency with the Highway Safety Manual (HSM). If the current Crash Experience Traffic Signal Warrant is sufficient, then this research should validate the warrant.
The products of this research project are intended to be used to: (1) determine whether installation of a traffic control signal at a specified intersection will improve its overall safety and (2) estimate the safety impacts of installing a traffic control signal at this intersection. The intersection may be located in an urban or rural area. The focus will be on typical intersection forms where (1) the through traffic movements cross at about a right angle and (2) STOP signs control the minor roadway. However, intersections with alternative types of traffic control and geometry will also be considered where feasible.
NCHRP Web Only Document 204, Crash Experience Warrant for Traffic Signals, is available. Also available at that link are a spreadsheet tool that implements the safety evaluation procedure developed in this project and a guide to conducting a safety evaluation. Project recommendations have been presented to the National Committee on Uniform Traffic Control Devices.
The traffic signal crash experience warrant within the Manual on Uniform Traffic Control Devices (MUTCD) is considered insufficient. It does not give the engineer a means to determine what improvements or degradation in safety can be anticipated from installing a traffic signal under the crash experience warrant. The basis of the current threshold of five or more crashes of the type correctable by traffic signal control is not known, although it has been used for many years. The current threshold of five or more crashes is not supported by research as the appropriate number to achieve positive results. In fact, some may consider the number to be arrived at arbitrarily and even members of the National Committee on Uniform Traffic Control Devices’ Signals Technical Committee do not know the origin of the threshold. All available research at this time is considered too complicated, too theoretical, and unusable to the practitioner. This research should provide the practitioner with the tools necessary to estimate the effectiveness and determine the safety impacts of installing traffic signals under this warrant.
With the introduction of the new AASHTO Highway Safety Manual and prior research that resulted in NCHRP Report 491, it is desirable to provide the engineer with a basis for the crash experience warrant that takes into account all available research and ensures consistency with the new Highway Safety Manual.
Task 1. Conduct a literature review, updating the one conducted in NCHRP Project 17-16.
Task 2. Survey practitioners to gather insights on the application of the existing crash experience warrant. Solicit input from the National Committee on Uniform Traffic Control Devices at their June 2013 meeting on the existing warrant and the project work plan.
Task 3. Develop proposed framework for estimating safety impacts. Submit a working paper that describes the framework and outlines the process for (1) developing the safety evaluation procedure and (2) using the procedure to develop the content of a proposed crash experience warrant.
Task 4. Develop procedure and tool to estimate safety impacts. The products of this task will consist of: (1) a working paper that documents the research conducted to develop the safety evaluation procedure, (2) a spreadsheet tool that automates the procedure, and (3) a user guide for the spreadsheet tool.
Task 5. Develop content of proposed crash experience warrant. The products of this task will consist of a working paper that documents the content of the proposed crash experience warrant, justifies the warrant language, and describes several case-study applications of the proposed warrant and safety evaluation procedure.
Task 6. Submit draft final report and guidebook.
Task 7. Submit final report and guidebook.