When you drive at night and your headlights illuminate a lane marking, it makes you feel safer, right? After all, bright pavement markings are designed to help you stay in your lane and prevent you from running off the roadway.
Called retroreflectivity, special materials in edge lines and lane lines create the brightness. With age and wear, that brightness deteriorates. Although we assume there is a correlation between pavement marking retroreflectivity and safety, up until now researchers have not been able to prove it.
“It’s a hard thing to measure,” said Paul Carlson, Texas A&M Transportation Institute (TTI) research engineer, who is also the head of TTI’s Operations and Design Division. Carlson is known for his pavement marking research and leads TTI’s unique Visibility Research Laboratory. “For one thing, in order to gather good information about safety, you would have to know the level of brightness, or retroreflectivity, a pavement marking had at the time someone ran off the roadway.”
As it turns out, Carlson had a near perfect opportunity to conduct a study, thanks to the Michigan Department of Transportation (MDOT).
For years, MDOT has measured the brightness of its pavement markings on individual roadways. Carlson realized that he could compare those brightness levels with the crashes occurring on those roadways.
“Michigan DOT is very serious about keeping its pavement markings maintained. If measurements show pavement markings were dull, they would be replaced. Comparing both dull and bright pavement markings with crash information, we were in a good position to determine if those retroreflectivity characteristics played a role in safety.”
So, Carlson’s study, “An Investigation of Longitudinal Pavement Marking Retroreflectivity and Safety,” got under way. Sponsored by the Federal Highway Administration (FHWA), he gathered crash data and retroreflectivity measurements from 2002 through 2008. He compared the measurements with certain types of crashes: single-vehicle, nighttime crashes that occurred during dry conditions and non-snow-time months.
After a lengthy and tedious process, Carlson completed the research in July 2012. He determined that fewer crashes occurred when pavement markers were brighter and newer.
“The evidence is pretty compelling,” Carlson says of the research. “It demonstrates that maintenance of pavement markings retroreflectivity can have a positive effect on safety. I’m confident of the results: Brighter pavement markings mean safer roadways.”
In the meantime, Carlson has been working with FHWA as it comes up with a retroreflectivity standard, which would help DOTs across the country know when pavement markings should be replaced.