AbstractVehicle speed in work zones is a significant concern to state transportation agencies and their construction partners. Prior research indicates that law enforcement vehicles within a work zone with active flashing lights result in reduced vehicle speeds. Placement of flashing blue lights on construction equipment during nighttime construction work has also been identified as a potential control measure to reduce speeds. The goal of this research study is to determine the impact of flashing blue lights on construction equipment on the speed of passing vehicles in mobile work zones. The research design consisted of a controlled experiment involving flashing blue lights mounted on the rear of a paver during mainline paving operations on three case study projects on high speed roadways at night in Oregon. Vehicle speed data were collected during multiple work shifts for each case study, both with and without the flashing blue lights on. The experimental results reveal that vehicle speed is affected by the presence of flashing blue lights during nighttime work. With the blue lights flashing and at distances upstream of the paver where the driver can see and react to the blue lights, mean vehicle speeds tended to be 4.3–25.7 km/h slower than when the blue lights were off. Closer to, immediately adjacent to, and downstream of the paver, the difference in the mean speed with the blue lights on was typically less or not significant; in some cases and mostly downstream of the paver location, the mean speeds were higher with the blue lights on than with the blue lights off. The speed differential (i.e., the speed prior to the work zone minus the speed in the work zone) was measured as 4.8–11.3 km/h greater with the blue lights turned on than with the blue lights off. The results support construction contractors and state departments of transportation for decision making about the use of flashing blue lights on equipment in work zones. The researchers recommend using flashing blue lights on paving equipment during nighttime operations if allowed by local laws to reduce the speed in the work zone and increase worker and driver safety. This research contributes to the construction industry by providing quantitative evidence of the extent to which flashing blue lights mounted on paving equipment impact vehicle speeds in work zones. Recently, all stakeholders, including the Oregon Department of Transportation, law enforcement, and contractors, have agreed to use the flashing blue lights on paving equipment in Oregon during the 2021 construction season.