Accelerating safety: Crash data to help improve work zones

We all know the two seasons in Illinois ― winter and work zones. While inching through work zones isn’t ideal for motorists, roadway construction and maintenance are integral parts of providing a safe and efficient transportation system. 

Keeping both drivers and workers safe in work zones is the Illinois Department of Transportation’s top priority. There’s a problem though, work zone crashes, especially those resulting in fatality and serious injury, are difficult to predict, which make them that much harder for IDOT to mitigate.

For example, from 2013 to 2016 national work zone crashes increased 42 percent. In Illinois, work zone crashes on IDOT roads accelerated, with 2016 seeing approximately 2,000 more crashes than 2013. Thankfully, however, work zone fatal crashes decreased in 2017 and even further in 2018.

Work zone safety professionals have often wondered if they can really assess safety by simply analyzing the data.

“Nationwide it has been very difficult for state departments to determine the real safety impact of work zones,” said Juan Pava, IDOT’s Safety Programs Unit chief. “In Illinois, we have been asking ourselves this question for many years without the ability to truly determine how we are impacting the safety of road users every time we set up a work zone area.”

That’s a challenge Illinois Center for Transportation and IDOT will address in project R27-186 Correlation between Work Zone Exposure and Work Zone-Related Fatal and A-Injury Crashes.

“Only a few states have attempted to analyze their work zone safety performance using exposure data in addition to crash data,” said Kerrie Schattler, a Bradley University Department of Civil Engineering and Construction professor and Principal Investigator of the project. “Thus, the results of this study will complement the state-of-the-art in work zone performance measures and trend assessment, and (they) will help other states interested in conducting such analysis in their own jurisdictions.”

ICT and IDOT went straight to work, analyzing work zone fatal ― known as K ― and type-A severe injury crashes from the Illinois Traffic Crash Database from 2013 to 2017. Data on exposure factors, such as the number of work zones, work zone length, and duration of the work zone were also collected.

While the research is ongoing, ICT and IDOT aim to quantify work zone crashes and injuries along with crash rates, including the above mentioned exposure variables, to have a better understanding of work zone safety performance in Illinois.

In the second phase of research, ICT and IDOT will determine the correlation between work zone crashes and the characteristics of 384 site-specific work zone locations, where in-depth analyses are already being conducted.

In addition to reviewing crash data from 2013 to 2017, the team has also quantified more than 20 work zone characteristics for these 384 sites, including variables such as road functional classification, work zone duration length, number of lanes and lane reductions, speed limits, types of road closure and activity, pre-work zone crashes and injuries, and traffic volumes.

ICT and IDOT’s review of crash frequencies and rates along with work zone characteristic data will help IDOT better understand the cause of work zone crashes with an eye toward predicting work zone crash severity at future work zone sites.

“Determining the correlation between work zone characteristics and work zone crashes, injuries, and fatalities will allow the department to take steps in moving towards zero fatalities in work zones,” Schattler said.

ICT and IDOT plan to use crash modification factors ― a measure of the safety effectiveness of a particular design element ― to examine the differences in work zone safety performance. They will then develop safety performance functions (SPFs) ― statistical models that estimate average crash frequency for a specific site.

Pava said SPFs will allow IDOT to “better determine the safest approaches to traffic control and protection in work zones.”

For example, let’s say IDOT is considering alternatives for an upcoming freeway maintenance project. The first option estimates a 120-day project completion, while the other considers only 100 days by using advanced technology. Which one is best?

In this hypothetical scenario, IDOT could predict which of the two projects offers the optimal safety benefits for drivers and workers using crash modification factors, the SPF model, and analysis of work zone comparisons.

“This research is not only looking at the development of crash modification factors and safety performance functions for the prediction of future work zone setups,” said Pava, who serves as the project’s Technical Review Panel chair, “but it will allow us to look back and help determine how changes in construction intensity, changes to traffic control standards, and work zone practices played a role in the safety of work zones in Illinois, (as well as) better allow us to continue moving towards the goal of reaching zero fatalities.”

ICT and IDOT hope to implement this SPF model upon the completion of the research in January 2020.