Researchers
About the research
Automated queue warning systems are a common safety countermeasure deployed in Iowa work zones. The project report documents the development and evaluation of crash modification factors (CMFs) for Iowa work zones with automated queue warning systems. The study utilized crash data from 2016 to 2023, focusing on crashes in smart work zones equipped with queue warning systems.
Data were collected from multiple sources, including the Iowa Traffic Critical Project (TCP) program, law enforcement-reported crash data, and the Iowa Roadway Asset Management System (RAMS). The TCP program provided detailed historical data on work zones during the study period and the various devices deployed as part of smart work zone systems. Crash data included spatial coordinates and dates, which were used to identify work zone-related incidents, while RAMS provided roadway characteristics relevant to CMF development.
Two buffer zones around the work zone’s dynamic message sign (for smart work zones) or around the start of the work zone location (for work zones without a queue warning system) were analyzed: a 1 mi upstream and 0.5 mi downstream buffer, and a 0.5 mi upstream and 0.5 mi downstream buffer. The evaluation involved the development of multiple regression models, specifically the negative binomial-P (NB-P) and Sichel models, which are well suited for handling overdispersed count data. These models were selected based on their log-likelihood values and cumulative residual (CURE) plots.
The results indicate that the presence of a queue warning system leads to a slight decrease in total crashes (up to 3.1%) and a significant reduction in fatal, major injury, and minor injury (KAB) crashes (up to 31.9%). The impact is more pronounced for the 1 mi upstream and 0.5 mi downstream buffer, suggesting that the queue warning system influences vehicle speeds around 1 mi upstream of the work zone. The reduction in crash severity is likely due to decreased vehicle speeds in the presence of a queue warning system. This study also explored connected vehicle data to assess speed profiles across four work zones and found consistent patterns of speed reduction in most of these work zones compared to periods without construction.
Despite promising results, the study acknowledges several limitations, including potential discrepancies in work zone location and duration data and the need for more precise data collection. In conclusion, implementing queue warning systems in work zones presents a viable strategy for mitigating work zone crash severity and enhancing road safety.