Maryland started a similar project this month on the eastbound span of the Chesapeake Bay Bridge in Annapolis using hot pink panels. Pennsylvania began experimenting with distance dots in 2000, but stopped adding them to roads in 2003 because transportation officials said they were not deterring the worst offenders.

Although many drivers might see tailgating as nothing more than an annoyance, it is a significant factor in many accidents, safety officials said. In Minnesota, rear-end collisions accounted for 28 percent of all crashes last year and resulted in 22 deaths, according to the State Office of Traffic Safety. And the number of rear-end crashes in the state increased to 24,820 last year, from 22,206 in 2002.

“It’s truly dangerous,” said Pat Hackman, executive director of Safe Communities of Wright County, a nonprofit traffic safety organization. “And some people might say, ‘Don’t we have bigger problems than this?’ And we certainly do. But I don’t think you quite understand how this is contributing to the bigger problems that we have.”

The idea of the dots on the highway here, explained on roadside signs, is for drivers to keep a distance of two dots between vehicles. The 225 feet between dots represents a driving interval of three seconds at the speed limit of 55 miles per hour.

Gordy Pehrson, traffic safety coordinator in the Office of Traffic Safety, said he hoped the dots would have a “halo effect,” with drivers taking the lesson to other roads as well.