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Lighting on snowplows: An accident countermeasure?

John D. Bullough
Lighting Scientist
Lighting Research Center
Rensselaer Polytechnic Institute

Vehicles for plowing snow and spreading abrasives most often are required to operate when visibility is compromised by poor weather. Research completed by Rensselaer Polytechnic Institute's Lighting Research Center for the National Cooperative Highway Research Program (NCHRP) has shown that paying attention to the lighting systems on snowplows could result in significant safety improvements and, perhaps, a reduction of accidents involving these vehicles.

Forward lighting
Of course, snowplows are operated during the time when visual conditions are poorest and least comfortable for the driver. At night, light from headlamps is reflected from snow particles and can cause discomfort. In a paper published in the proceedings of the 2001 Progress in Automotive Lighting Symposium,1 research on forward visibility while driving during poor weather, such as snowfall, is described. Previous research suggested that using narrow-beam lamps, mounted away from the driver's line of sight, would result in the lowest amount of back-scattered light toward the driver. Of interest, the driver's side headlamp on a snowplow is often mounted where it will result in the greatest amount of back-scattered light.

Field studies conducted during snowplowing operations confirmed that narrow beams and mounting positions furthest from the line of sight, such as auxiliary headlamps mounted on the passenger side of the vehicle, can be effective and low-cost solutions to reducing discomfort and glare while driving during adverse weather. Previous research also hinted that changing the spectrum of forward lighting to "warmer" or "yellower" colors would tend to reduce discomfort, but the effects of changing from white to yellow headlamps were found to be relatively small, compared to using lamps with narrower beams and off-axis mounting positions.

Rear lighting and signaling
Rear lighting systems on snowplows serve two distinct purposes:

  • to alert other drivers that the plow is on the roadway
  • to provide information about the plow's relative speed and distance

A presentation given at the 2001 conference of the Illuminating Engineering Society of North America2 describes research on the characteristics of lighting and signaling systems to meet both of the objectives listed above. Flashing and strobing lights are used on snowplows by many agencies, who have recognized the strong attention-getting properties of these systems. 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 meeting the second objective listed above, that is, providing cues about the plow's relative speed and distance as other drivers approach it from behind.

To test this idea, a prototype steady-burning light bar using light-emitting diodes (see Figure 1) was developed and field-tested on a snowplow, which was also equipped with flashing lights. The ability of observers to detect the plow's deceleration while riding behind it was measured for both lighting systems during snow plowing operations at night. The average time to detect the plow's deceleration was significantly shorter with the steady-burning light bar than with flashing lights. In addition, observers rated the steady-burning light bar as providing better visibility and confidence for judging speed and distance than the flashing lights. The prototype light bar could easily be adapted to existing maintenance vehicles as a retrofit, or it could be incorporated into specifications for new vehicles.

Acknowledgments
The research described here was conducted as part of NCHRP Project 6-12 with cooperation from the New York State Department of Transportation (NYSDOT). NCHRP and NYSDOT are gratefully acknowledged for their support of this work.

References

1. Bullough, John D. and Mark S. Rea (2001). Forward vehicular lighting and inclement weather conditions. Progress in Automotive Lighting Symposium '01, Darmstadt, Germany. 2. Bullough, John D., Mark S. Rea, Richard M. Pysar, Hany K. Nakhla and Duane E. Amsler. (2001). Rear lighting configurations for winter maintenance vehicles. Proceedings of the Illuminating Engineering Society of North America Annual Conference, Ottawa, ON, Canada.

For more information, please contact John D. Bullough at (518) 687-7100 or at bulloj@rpi.edu.