February 17, 2020

Rumble strips get attention of UM experts

Rumble strips on the sides of some stretches of Maine’s interstate highways have reduced the number of accidents caused by sleepy drivers by 37 percent since the mid-1990s, Per Garder, a University of Maine associate professor of civil engineering, said this week.

Garder and fellow UM civil engineering professor John Alexander studied rumble strips in 1994 and recommended they be etched onto the sides of Maine highways at what today is a cost of $1,900 per lane mile. Carving the four strips onto the edges of both south and northbound highway lanes costs $7,600 a mile.

The two reported that for every $1 spent, $100 in medical costs would be saved. The state accepted the recommendations and began adding the strips to Maine’s major highways.

Much of the Maine Turnpike and I-95 have the strips today.

Recent research by the Department of Transportation bear out the professors’ earlier enthusiasm, Garder said.

“We’re happy with what the DOT has found out,” Garder said. “It has a clear effect on safety.”

The grooved pavement, typically positioned along the inside edge of the breakdown lane and outside edge of the passing lane, cause a car to rumble and shake when its wheels begin to travel on it. That can alert a sleepy or inattentive driver to the fact that he is heading off the road.

Still, the latest findings show that there is an inherent limit to what it can do, Garder said.

Not all dozing drivers will be awakened by the rumble strip. And while many who are awakened will take appropriate corrective action, others will overcorrect and still wind up in an accident, Garder said.

A rumble-strip overcorrection may have caused the accident north of Tampa, Fla., Tuesday that killed two Ellsworth residents, the Florida Highway Patrol reported.

Statistics regarding overcorrection are hard to develop, said Duane Brunell, a Maine DOT engineer with the safety management group. But he said his professional guess is that it’s not a major cause of accidents.

Regardless, hitting the rumble strip anytime other than when one is intending to go into the breakdown lane is a sign that the car is going where it shouldn’t, he said. Whether caused by sleepiness, fatigue or reaching for a music CD or ringing telephone, inattention leads to accidents.

“Driving is a full-time activity,” Brunell said.

Garder said that while rumble strips may be responsible for some accidents – in one case a motorcyclist drove onto the strip and lost control of his bike – it’s all part of a calculated trade-off in trying to save lives.

As an example, Garder explained that guardrails are put in place to avoid more serious crashes where cars would plunge off a bridge or down a steep embankment. But it’s clear that because they are there cars sometimes hit them.

The DOT has milled 300 lane miles of rumble strip into Maine’s highways. That includes about 75 miles of interstate. Additionally, the Maine Turnpike Authority maintains its own strips.

They are considered so effective that strips are now seen in most states, Brunell said.

Maine is about to study the idea of using strips along the center-line and in two-way roads other than highways, he said.

The new study will be part of the effort to reduce the number of accidents in Maine, he said. There are about 1,700 head-on collisions a year which result in 45 to 50 fatalities, Brunell said.

On average, 9,000 vehicles veer off roads and crash each year-most because of sleepy drivers. About 75 people die in those accidents annually.

The total number of accidents in Maine approaches 40,000 per year, which results in 165 to 190 fatalities.

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