Estimating the Impact of Work Zones on Highway Safety

Investigating the operational and safety impacts of work zones on traffic are of great interest to transportation agencies. Despite the increasing attention in modeling work zone crash frequency, only a limited number of studies directly examined the change in crash rates under work zone conditions versus the corresponding non-work zone conditions. The main research question is thus whether or not a given roadway experiences increased number of crashes in the presence of a work zone. Another important goal of this study is to address the main research question using a large number of relatively long-term work zones. This is a challenging task because a major effort for building a comprehensive data set of a large number of work zones is needed. To answer this important question, an integrated data set is created by aggregating information from multiple data sources for sixty long-term work zones. Then descriptive analysis is performed to examine the characteristics of work zone crashes. Preliminary analysis results show that the crash rate increased by 24.4 percent under the work zone condition. To further statistically quantify the impact of work zones on traffic safety, negative binomial regression models are developed to identify relationship between a set of covariates and the crash counts aggregated by time and crash severity. An indicative variable is incorporated into the model to represent the work zone and non-work zone conditions for the studied sites. Overall, the descriptive analysis and modeling results suggest that the presence of work zones significantly increases the risk of crashes on roads.