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Troy, N.Y. -  11/21/2011

States Implementing Wipers-on, Headlamps-on Law See Reduction in Fatal Crashes According to Lighting Research Center Study

Troy, N.Y. – In the past few decades, many states in the U.S. have enacted States implementing “Wipers-on, Headlamps-on” law see reduction in fatal crashes "wipers-on, headlamps-on" laws requiring the use of vehicle headlamps while driving during the daytime in weather conditions that require the use of windshield wipers. The logic for doing so seems simple enough—vehicles with their headlamps (and tail lamps) on will be more conspicuous to other drivers. But legislators in some states have resisted passing such laws because, until now, there was no direct evidence suggesting these laws have any meaningful benefits.

The Lighting Research Center (LRC) at Rensselaer Polytechnic Institute recently found that the odds of being killed in a multiple-vehicle crash during daytime rain were about 8 percent lower after states enacted wipers-on laws, according to research recently published in the journal Safety Science.

LRC Senior Research Scientist and principal investigator John Bullough examined data from the National Highway Traffic Safety Administration (NHTSA) on fatal crashes during daytime and nighttime and during clear and rainy weather. He evaluated fatal crashes from several states that enacted wipers-on, headlamps-on laws and found statistically significant reductions in the proportion of daytime crashes in rainy weather after legislation was enacted, relative to the period before enactment. He notes that the relationship was found only for multiple-vehicle and not for single-vehicle crashes.

"Headlamp use during the daytime, even in the rain, doesn't add much to the total amount of light on the road, but it would make one's car more visible to others, so the effect should only be seen when more than one vehicle is involved in a crash," explained Bullough, who coordinates the LRC's transportation and safety research.

In an earlier paper presented this fall at the International Symposium on Automotive Lighting in Germany, Bullough compared rainy-weather crash data for dawn and dusk periods to those during the rest of the day. He found the reduction in multiple-vehicle crashes in rain during dawn and dusk after the enactment of wipers-on laws was four times larger than during the brighter part of the day, which is consistent with an earlier published study from Japan that showed that cars with their headlamps on were four times more noticeable during dawn and dusk than during the rest of the daytime.

"Finding statistical associations between lighting and crashes is important, but crash statistics alone can't prove cause and effect. For example, we don't know how many drivers in these states actually used their headlamps in the rain. But the agreement between the crash data and the noticeability data gives us more confidence in relating the visual benefits of lighting to safety," said Bullough.

The LRC's studies were supported by the members of the Transportation Lighting Alliance (TLA): Automotive Lighting, Hella, OSRAM Sylvania, Philips Automotive Lighting, and Visteon. Bullough's article in Safety Science can be found online at:


About the Lighting Research Center
The Lighting Research Center (LRC) at Rensselaer Polytechnic Institute is the world's leading center for lighting research and education. Established in 1988 by the New York State Energy Research and Development Authority (NYSERDA), the LRC conducts research in light and human health, transportation lighting and safety, solid-state lighting, energy efficiency, and plant health. LRC lighting scientists with multidisciplinary expertise in research, technology, design, and human factors, collaborate with a global network of leading manufacturers and government agencies, developing innovative lighting solutions for projects that range from the Boeing 787 Dreamliner to U.S. Navy submarines to hospital neonatal intensive-care units. In 1990, the LRC became the first university research center to offer graduate degrees in lighting and today, offers a M.S. in lighting and a Ph.D. to educate future leaders in lighting. Learn more at

About Rensselaer Polytechnic Institute
Founded in 1824, Rensselaer Polytechnic Institute is America's first technological research university. Rensselaer encompasses five schools, 32 research centers, more than 145 academic programs, and a dynamic community made up of more than 7,900 students and more than 100,000 living alumni. Rensselaer faculty and alumni include more than 145 National Academy members, six members of the National Inventors Hall of Fame, six National Medal of Technology winners, five National Medal of Science winners, and a Nobel Prize winner in Physics. With nearly 200 years of experience advancing scientific and technological knowledge, Rensselaer remains focused on addressing global challenges with a spirit of ingenuity and collaboration.