Work Zone Safety Performance on Illinois State Routes

The Illinois Department of Transportation (IDOT) faces challenges in understanding the causes of increased work zone crashes. Although direct safety metrics of work zone (WZ) crashes are useful, they do not completely reflect work zone safety performance. A research project was commissioned to examine the correlation between WZ exposure and crashes and fatalities/injuries, which included three main objectives. The first objective was to more clearly quantify and report yearly trends on WZ crashes with an emphasis on fatal and injury crashes with respect to WZ exposure variables. Data were recorded for WZ traffic crashes from 2013 to 2017, WZ characteristics for IDOT roads, and roadway characteristics. Work zone safety performance measures were determined for the following: WZ total crashes, WZ fatal (K) and A-injury crashes, WZ fatal/injury (K, A, B, C) crashes, WZ fatalities/injuries, number of IDOT work zones, WZ miles, WZ days, and WZ day-miles. Crash rates were calculated for the four crash types and four WZ exposure variables. Annual trend analyses were conducted for 16 crash rates, which provided additional insights in WZ safety trends in Illinois. The second objective was to conduct an in-depth analysis of site-specific WZ sites and characteristics in Illinois to develop prediction tools. Data for 384 sites were used in a model calibration and validation study, using statewide databases. Safety performance functions (SPFs) for predicting total and fatal/injury WZ crashes were developed and supplemented by an Excel tool to assess WZ safety, and crash modification factors (CMFs) for WZ length and duration were derived. The third objective was to identify gaps in existing WZ data in Illinois and make recommendations on data needs. Several issues with the WZ data currently collected by IDOT were identified. FHWA’s Work Zone Data Initiative manuals provide recommended practices for collecting and managing uniform WZ activity data across jurisdictional and organizational boundaries. These manuals were used as the basis for recommending WZ data collection improvements in Illinois. This report discusses data collection procedures, issues, and assumptions made to overcome them, as well as the annual work zone crash rates with recommended exposure variables. The SPF and CMF development process and resulting SPF models are presented, along with how they can be applied to improve work zone safety. Finally, this report presents data needs and recommendations for collecting and maintaining work zone data with higher levels of accuracy that also support the FHWA work zone data initiatives. Overall, this research will aid in assessing safety aspects of work zones, which will enable IDOT to make progress towards achieving zero WZ fatalities.