Effectiveness of Green Strobes on Winter Maintenance Vehicles and Equipment

Project Summary


Project Number: SPR-1692
Contract Number: 2019-0442
Status: Complete
Start Date: 06/04/2019
End Date: 08/31/2020
Keywords: Winter maintenance, warning light, green strobe, safety, visibility, snowplow, flashing pattern, conspicuity, glare


Snow removal and deicing activities are performed by roadway agencies to enhance winter mobility and safety. Due to slower travel speeds during these operations, low visibility and reduced pavement friction, safety and collision avoidance remain persistent concerns. To improve the visibility of winter maintenance vehicles, the Michigan Department of Transportation (MDOT) has added green lights to the warning system of winter maintenance trucks (WMTs) since 2016.

This study investigated the degree to which the visibility can be affected by including these green lights. First, the current state of practice by all state transportation agencies was explored through a comprehensive survey that shows most agencies considered using alternate colors in addition to amber. To evaluate impacts of adding green lights to the warning system of WMTs in terms of visibility, 37 warning light configurations were generated using various color combinations (green and amber) and flashing patterns (single and quad) on the back side (LED) and/or top (beacon) of the WMTs. These configurations were evaluated to identify the most effective ones based on feedback provided by several expert and public panels. Three sets of experiments (static, dynamic and weather) were designed and implemented to evaluate the visibility effectiveness in different contexts (day versus night conditions, clear versus snowy weather and static versus dynamic scenarios). Each of these experiments contains multiple tests that aimed to identify different measures to assess the light configuration efficiency. Panels of experts and from the public were employed to conduct the experiments, and the test results were evaluated using statistical analyses. Conspicuity during the day and glare at night were the two main criteria with statistically significant results that were used to compare various configurations. The results showed that adding green lights with a single flash pattern to amber warning lights improved the conspicuity significantly, while keeping the glare at an acceptable level relative to configurations using only amber warning lights.


Final Report


Multimedia: Green Strobes Increase Visibility and Safety for Winter Maintenance Vehicles



Project Organization


MDOT Research Manager MDOT Project Manager Performing Organization(s)
André Clover

Jim Gaus &

Melissa Longworth

Michigan State University