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Executive Summary Introduction The crash experience warrant in the Manual on Uniform Traffic Control Devices (MUTCD) specifies three criteria that must be met before a traffic signal can be considered for installation at an intersection (FHWA, 2009). One of these criteria requires that five or more crashes of a type susceptible to correction by a signal must have occurred at the subject intersection during a one-year period. The basis of this threshold of five or more crashes is not known, although it has been used for many years. This lack of historical reference has led some practitioners to consider the threshold number to be arrived at arbitrarily. The MUTCD also states that, âA traffic control signal should not be installed unless an engineering study indicates that installing a traffic control signal will improve the overall safety and/or operation of the intersection.â However, there is no guidance offered in the MUTCD as to how the overall safety impact of the signal can be quantified. 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 research approach was focused on the development of a procedure for evaluating the safety of stop-controlled and signal-controlled intersections. This procedure was then used to evaluate the change in safety associated with signal installation. The findings from this evaluation were used to develop the proposed crash experience warrant. The safety evaluation procedure incorporated the safety prediction methodology documented in Part C of the HSM. Conclusions and Recommendations Section 4C.01 of the MUTCD states that, âA traffic control signal should not be installed unless an engineering study indicates that installing a traffic control signal will improve the overall safety and/or operation of the intersection.â However, there is no guidance offered in the MUTCD as to how the overall safety impact of the signal installation can be quantified so as to ascertain whether safety has been improved. The MUTCD provides a crash experience warrant that serves as a first step of the engineering study process. Satisfaction of the crash experience warrant is an indication of likely safety improvement through signal installation. Once the warrant is met, the subsequent steps of the engineering study are then undertaken to confirm that signal installation will improve overall safety. The HSM is being used by some practitioners during the engineering study to confirm whether signal installation will improve overall safety. Specifically, the HSM is being used to quantify the reduction in expected crash frequency and severity associated with the signal installation. A procedure was developed for quantifying the safety effect of signal installation. This procedure can optionally be used as part of the engineering study process. It is based on the predictive methods in the HSM. Observed crash data for one or more recent years can be used with the procedure to obtain a more reliable result. The procedure can be applied using a hand calculator, but it was also incorporated in a spreadsheet tool to facilitate implementation. The procedure considers total intersection crashes and crash severity. The aforementioned procedure was used to develop revised content for Criterion B of the crash experience warrant. Application of the procedure to a range of typical intersection conditions indicated that there is a threshold value of observed crashes beyond which signal installation is likely to improve safety. However, the threshold value was found to vary by area type, intersection legs, and number of vii
lanes on each intersection approach. As a result, a table of threshold values was prepared to include different values for logical combinations of area type, legs, and lanes. It is recommended that the proposed crash experience documented in Chapter 5 be incorporated into the next edition of the MUTCD. viii
