Engineering Study Guide for Evaluating Intersection Improvements

Implementation Products

"A 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" (Chapter 4C, MUTCD). The Intersection Safety Evaluation Guidebook can be used to evaluate the safety effect of signal installation and other intersection improvements. The Engineering Study Guide can be used to evaluate the operational effect of signal installation and other intersection improvements.

Intersection Safety Evaluation Guidebook and User Manual. J. Bonneson and K. Laustsen. This document describes the use of a procedure for evaluating the safety of alternative intersection configurations and traffic control types. It includes guidance for conducting the evaluation and guidance for the use of the Intersection Safety Analysis Tool (InSAT). This tool can be used to automate the calculations associated with the evaluation. The equations used in InSAT are implemented in a spreadsheet. The document and spreadsheet are products of NCHRP Project 07-18.  GUIDEBOOK    SPREADSHEET

Note: A 2022 security change by Microsoft prevents Excel files with macros (i.e., with the .xlsm extension) from running unless the analyst changes the file properties to unblock the file macros. Right-click on the filename, select Properties, select General, in the Security section (at the bottom) check the "Unblock" checkbox, and select OK.

NCHRP Report 457: Evaluating Intersection Improvements: An Engineering Study Guide. J. Bonneson and M. Fontaine. This interactive guide describes a process for evaluating the operational effectiveness of various intersection improvements. It focuses on problematic unsignalized intersections.  The evaluation process is defined to consist of three stages: (1) the identification of alternative control strategies and geometric improvements; (2) the conduct of an engineering study to evaluate the operational effectiveness of viable alternatives; and (3) the selection of the best alternative. The Guide can also be used to evaluate existing traffic signals; this evaluation can be used to justify removal of inappropriate signals.  PRODUCT (unzip all files into a common folder) 

Research Report

NCHRP Project 07-18: Crash Experience Warrant for Traffic Signals, Final Report. J. Bonneson, K. Lausten, L. Rodegerdts, and S. Beaird. A procedure was developed for quantifying the safety effect of signal installation and other intersection improvements. The procedure is based on the predictive methods in the Highway Safety Manual. The procedure was used to develop a proposed crash experience warrant for traffic signals. The warrant criteria are sensitive to area type, intersection legs, and number of lanes on each intersection approach. A revised crash experience warrant was prepared and recommended for inclusion in the MUTCD.   REPORT

NCHRP Project 3-58: Assessing Traffic Control Signal Installations Using Capacity Analysis and Simulation, Final Report.  J. Bonneson and M. Fontaine.  The objective of the project was to develop guidelines for using capacity analysis and simulation in engineering studies. To satisfy this objective, an Engineering Study Guide was developed. This report documents the research activities undertaken to develop the Engineering Study Guide.  REPORT 

White Papers

Effect of Signalization on Safety.  The issue addressed in this paper is the effect of signalizing an intersection on the frequency of intersection-related crashes.  The safety literature was reviewed to resolve this issue. The evidence found is inconclusive when signals are added without other changes to the intersection. Severe crashes tend to be reduced but the addition of signals may increase crash frequency under some conditions. PAPER