As speed limit increases, so will risk factor on road

June 28, 1995|By Frank D. Roylance | Frank D. Roylance,Sun Staff Writer

JACKSON -- George Messner's first mistake was driving 69 mph on Interstate 95 just north of the Perryville toll plaza yesterday. That's where Tfc. Ernie Tullis of the Maryland State Police was waiting in an unmarked sedan with his laser gun.

"I was hoping I was doing 65," Mr. Messner said. But the speed limit is 55, and his comment clinched a $60 ticket for the Sea Cliff, N.Y., man.

Mr. Messner might have avoided the whole mess had he made the trip after daybreak on Saturday, when the speed limit on 265 miles of Maryland's rural interstates will increase to 65 mph.

Officials say the limit will be strictly enforced. But hazards far greater than traffic tickets lie in the science of speed, researchers warn. At 65 mph and above, accidents will be harder to avoid, and much more violent. To believe otherwise, they say, you must repeal the laws of physics.

"The interstates are the safest roads for high speed travel. But that does not mean that . . . a crash at 65 mph is going to be a kindly thing," said Susan P. Baker, a health policy professor at the Johns Hopkins University School of Hygiene and Public Health and an expert on injury prevention.

In the 40 states where rural speed limits were increased to 65 mph in 1987 or 1988, according to the U.S. Department of Transportation, deaths on the affected interstates climbed 20 percent to 30 percent. An additional 500 people died each year.

In Maryland, the higher speeds will become legal as soon as state highway crews remove the metal 5's that now cover the 6's on the new speed limit signs.

State police spokesman Mike McKelvin said troopers have been told to hold the line at 65. "We will have a no-excuse, no-tolerance policy, especially on 65-mph road ways," he said. As a practical matter, Maryland drivers haven't waited for the new law. Speeds on rural interstates averaged 63.7 mph last year, up 5 mph from the year before, according to the State

Highway Administration. Fifteen percent of drivers exceeded 70.1 mph.

The state had no data on interstate fatalities last year.

The General Assembly, finally free of former-Gov. William Donald Schaefer's threatened vetoes, passed the speed limits bill in April, and Gov. Parris N. Glendening signed it.

On a 50-mile highway trip, the added 10 mph will save you nine minutes. On a 100-mile journey you'll arrive 17 minutes sooner. But experts say the added convenience comes with more

highway mayhem.

Simple physics

It's simple physics, said David E. Cole, a professor of mechanical engineering and an auto safety expert at the University of Michigan.

Tougher drunken driving laws and better safety equipment have helped cut auto fatalities by 21 percent since 1980. But "if you're driving faster and you hit something, it's a more deadly accident," Dr. Cole said.

Consider the hypothetical Maryland family headed for Deep Creek Lake this weekend on Interstate 68, one of the rural interstates slated for the 65-mph limit. In addition to all their baggage, the family car is also packing a lot more kinetic energy than it was at 55 mph.

That's because the energy in a moving vehicle increases with the square of its speed. In other words, a crash at 40 mph is not twice as violent as one at 20 mph -- it's four times as violent.

At 65 mph, our family's station wagon is traveling 18 percent faster than at 55 mph. But the energy unleashed in any crash at 65 mph -- and the danger -- is 40 percent higher.

If Dad pushes his luck to 75 mph, he's playing with nearly 90 percent more destructive energy.

Tougher to stop

The higher speeds exact another toll -- longer stopping distances.

"Suppose you turn a corner and notice a car stopped in your lane. The average time it takes a person to start [braking] is about 2.5 seconds," said Dr. Ian V. Lau of the General Motors Research and Development Center in Warren, Mich.

In all, you need 400 feet of clear highway to make a safe stop from 55 mph. From 65 mph, the distance increases by 116 feet.

A crash into a tree or a bridge abutment at 55 mph or 65 mph is probably not survivable. In either case, "it's probably going to crush the car all the way to the back seat," said Ralph J. Hitchcock, director of crash-worthiness research at the National Highway Traffic Safety Administration.

But more highway accidents involve a crash into another vehicle, a "softer" target that absorbs about half your vehicle's kinetic energy. In other words, Mr. Hitchcock said, a crash into a parked car at 55 mph is like hitting a brick wall at 27.5 mph.

"That is within the range of survivability," he said.

Hitting the same car at 65 mph is like smashing into a wall at 32.5 mph, and "that's starting to get a little above what the federal standards are. You start to see structural collapse."

Actually, the government requires that auto manufacturers test their cars for survivability in rigid barrier crashes up to 35 mph, said Dr. David Viano, head of biomedical science at General Motors.

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