There were 774 fatal crashes in work zones in 2020, which resulted in 857 deaths, including 51 highway workers, according to the U.S. Department of Transportation and Federal Highway Administration. Work zones temporarily change the way a roadway operates by reducing or narrowing lanes, eliminating the shoulder, introducing roadside or median barriers, or shifting traffic onto a detour route. Traffic engineers strive to mitigate the risks these changes can cause through thoughtful work zone planning and design, but the effectiveness of their approaches can be difficult to measure. Implementing measurable work zone safety goals helps agencies monitor the performance of their work zones and make improvements to their work zone safety policies and practices. 

Evaluating the existing performance of the roadway and estimating the likely impacts of the geometric and traffic control changes brought about by the work zone provide a baseline for the expected safety of that work zone. From this baseline, changes to the work zone design or improvements to work zone technology can be considered to help mitigate the risks of serious crashes and set target safety goals. The design team can start with these three questions:

What is the scope and scale of the work?
Work zone safety goals first consider the scope and scale of the work being performed. For example, a work zone at a single intersection may result in a capacity reduction of the roadway or a short detour, leading to limited safety impacts. On the other hand, projects on major routes that require significant detours may change travel patterns and volumes on a broader roadway network, even beyond the signed detour route, impacting safety regionally. Understanding where traffic will be impacted helps the project team set the boundaries for how existing safety performance will be measured and work zone safety performance will be monitored.

What modes will be impacted?
When setting work zone safety goals, all modes using the impacted facilities must be considered, including pedestrians, cyclists and transit users. Work zones may introduce risk factors for vulnerable road users by making bus stops more difficult to access, reducing buffer space between vehicles and cyclists, increasing walking trip lengths through detours, creating sight obstructions, and requiring more of the driver’s attention when following the work zone traffic control. Understanding the crash trends for all modes on the broader roadway network prior to construction helps the project team develop goals that are appropriate for the local area.

What work zone strategies can be implemented to support our safety goals?
Once the existing safety performance of the network is understood, the project team can begin evaluating the work zone design for its potential impact on safety. Work zones must be designed to clearly communicate changes in traffic control, lane assignments, detours, and other critical information to drivers, pedestrians, cyclists and transit operators. Focusing on reducing queue length not only reduces delay for drivers but also the chance for rear-end crashes at the end of the queue. The project team must also see that emergency responders can access crashes within the work zone and warn upstream drivers of any incidents to reduce the risk of secondary crashes. During this process, various work zone configurations can be evaluated, including: traditional lane drops; lane shifts; zipper merges, which reduce queue lengths; detours to help redirect traffic from the area under construction with limited capacity; and/or additional advanced signage to warn drivers of changing conditions. Work zone configurations can be modeled to help predict the effects on mobility in the area, and areas of congestion can be addressed to reduce safety impacts.

While the responsibility falls on drivers to maintain the speed limit and obey traffic control and all applicable laws in a work zone, certain measures can be implemented to make it easier for drivers to safely navigate them. Work zone safety goals help agencies monitor and measure the safety performance of their work zones so that they can be continuously improved to reduce the risk for roadway users and construction workers alike.


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Allison is a senior civil engineer at Burns & McDonnell. Her complex crash models and safety crash analyses have informed interstate, highway and bridge design and reconstruction projects nationwide.