In this report, Texas Transportation Institute researchers documented the efforts undertaken to investigate and categorize the different types of work zone intrusion crashes that occur on California roadways, and to conduct a detailed comparative critique of how each of the various countermeasures available may mitigate those types of work zone intrusions. Researchers used the New York State Department of Transportation work zone incident database and telephone surveys of California Department of Transportation and highway contractor personnel in California to gain insights into the frequency, characteristics, and crash sequences that comprise vehicle intrusion crashes at California work zones. Intrusion crashes make up a relatively small portion of crashes at work zones, and comprise a greater proportion of nighttime crashes than daytime crashes, although most intrusion crashes happen during daytime work operations. The biggest share of vehicle intrusion crashes occurs at lane closure operations. Intrusion crashes also occur at mobile operations, flagging operations, and during traffic control set-up and removal activities. When intrusions crashes occur, they most often involve collisions with work vehicles/equipment or work materials/debris rather than with a highway worker. In addition, a significant portion of intrusion crashes are the result of deliberate driver decisions and actions to enter the work area.
Several countermeasures were identified to address intrusion crashes. Some emphasize increased attention to current procedures or possible expansion of procedures, and are fairly low cost to implement. Others are technological countermeasures, and can have fairly significant costs associated with them. An assessment of implementation costs to possible reduction in work zone intrusion crash costs was performed and is documented in the report. Based on these findings, researchers developed guidance on which work zone intrusion countermeasures are most appropriate for a given set of roadway conditions and planned work zone activities.