PAPER # 14 : REAR LIGHTING CONFIGURATIONS FOR WINTER MAINTENANCE VEHICLES

Winter maintenance vehicles for snowplowing often operate when visibility is compromised. Rear lighting on snowplows serves two purposes: to alert drivers of nearby vehicles that the snowplow is on the roadway, and to provide cues to those drivers about the snowplow's relative speed and distance. Flashing and strobing lights have been used on snowplows by many departments of transportation, who consider these lights as having high conspicuity and attention-getting properties. However, most accidents involving snowplows are rear-end collisions by other vehicles, and previous research supports the idea that flashing or strobing configurations are less effective than steady-burning lights at providing cues about relative speed, distance and closure to drivers approaching a snowplow from behind. To test this concept, a prototype steady-burning light bar using light-emitting diodes was developed and tested on a snowplow vehicle, which was also equipped with conventional flashing lights. The ability of subjects following snowplows to detect deceleration of the snowplow was measured with each lighting configuration during nighttime field tests conducted while snow was falling. The mean time to detect closure was significantly shorter with the steady-burning light bar than with flashing lights. Subjective ratings of visibility and confidence for judging speed and distance were also higher with a steady-burning light bar than for the conventional system. The prototype light bar configuration could easily be adapted to existing snowplow vehicles as a retrofit, or it could be incorporated into specifications for new maintenance vehicles. BACKGROUND A major problem experienced by snowplow operators is the inability of other vehicle drivers to maneuver safely near the snowplow. Around 70% of all accidents involving snowplows involve collisions into the rear of snowplow trucks. On the surface, the solution to this problem seems to be one of increasing the conspicuity of the snowplowing vehicle. While conspicuity is indeed important, equally important is improving the ability of other drivers to judge the distance, direction and speed of the snowplow relative to their own vehicles, especially in a driving environment where falling snow, oncoming headlights and other flashing signals can contribute to glare and fatigue. Rear lighting on snowplow vehicles should serve two distinct purposes: • Provide a conspicuous signal to other drivers that the plow is on the road • Provide cues about the plow’s operating speed, direction and distance, relative to other vehicles Lighting systems that are highly conspicuous (e.g., strobe lights) are often poor at providing speed and distance cues, and vice versa. The challenge of rear lighting and signaling for snowplows is finding an effective balance between these purposes. Review of the relevant literature on rear lighting and signaling shows that several factors affect visibility of a vehicle to other drivers: • Mounting location • Temporal light characteristics • Spatial light characteristics • Luminous intensity Significant cloud accumulation behind the truck can occur while plowing snow. The most effective mounting location for rear lights in this case is as high as possible in order to ensure that the lights will clear the cloud behind the truck. A number of agencies in the U.S. and Canada specify high mounting locations for rear lights, including the Department of Transportation in New York State and the Ontario Ministry of Transport. Such specifications are in general agreement with the recommendations of Marsh. In addition, a high mounting location permits the maximum lamp intensity to be visible from the furthest distance away from the plow truck. As a following vehicle approaches