Sunday July 27, 2008
Bad drivers aren\’t the only cause of accidents
The news item reported that police had issued 363 speeding tickets in a single weekend, on the highway that runs through northern Alberta between Fort McMurray and Edmonton.
Most of its 443 km is a two-lane undivided road running through boreal forest. For oilsands workers flush with cash, those long empty stretches invite speeding.
So far, this year, RCMP and provincial sheriffs have issued over 2,000 speeding tickets. At least six people have died in crashes; another ten were killed last year. Between 2001 and 2005, that highway counted more than 1000 collisions; 25 people died, 257 were injured.
“It\’s known as the death highway,” RCMP Sgt. Larry Bellows commented.
Presumably, the federal and provincial governments agree. Ottawa will put up $150 million to rebuild the road as a divided highway; Alberta will provide the balance, estimated at $530 million.
It\’s an interesting contradiction. Police and politicians both seem to recognize that the highway itself is dangerous, inadequate for the traffic on it. Heavy equipment for oilsands development, for example, can impede both lanes, both directions, causing long delays and frustrations.
Yet people such as Sgt. Bellows insist that the highway itself is safe, if motorists would just obey the posted speed limits.
Assumptions, not always right
In reality, speed limits have very little to do with safety.
People make all kinds of assumptions about traffic safety. Most of them are only partially true.
Take the argument that lowering speed limits will save lives. It\’s true that traffic deaths in the U.S. dropped when President Nixon imposed a nationwide speed limit of 55 mph. But other factors also affected that reduction — seat belts; crash design in the cars themselves; braking systems that prevented skids; more barriers between traffic lanes…
And an often overlooked factor – highways departments began placing sand barrels in front of bridge abutments and overpass pillars. Cars that veered out of their lanes hit yielding sand rather than rigid concrete or steel.
When states began raising speed limits again in the 1990s, the death rate should have gone up, according to conventional wisdom. It didn\’t. It continued to drop.
In fact, noted Csaba Csere, Editor in Chief of Car and Driver magazine, “the fatality rate dropped more in the states that raised speed limits than in those that didn\’t.”
The difference is the key
The University of Minnesota\’s State Highway Experimental Station was mandated to examine all kinds of factors about traffic accidents. They concluded that speed itself has little relationship to safety.
The significant factor is the difference in speed. Highways engineers call it the “standard deviation in mean speed.” As I understand it, approximately one-sixth of vehicles can be over or under the standard mean speed without significantly increasing the risk.
To put that in practical terms, 100 km/hr is no safer than 110, or 120, or even 160 km/hr — as long as everyone is doing roughly the same speed. The risk comes when someone doing 160 km/hr catches up to someone doing only 80 km/hr — and that risk is exactly the same as someone doing only 80 km/hr and hitting a concrete wall.
Speed itself does not kill. Sudden change of speed does. The greater the change, the greater the risk of injury or death.
It doesn\’t matter what caused the change – falling asleep, rear-ending another vehicle, hitting a moose…
If you\’ve driven through Canada\’s national parks recently, you\’ll have seen high fences on both sides of the highway, to prevent large animals from wandering onto the road. That helps reduce one potential cause of sudden deceleration.
Dangerous intersections
I was introduced to the importance of highway design by Dr. Arthur Upgren, professor at Wesleyan University in Connecticut, and Senior Research Scientist at the Department of Astronomy at Yale University. He has the kind of probing mind that\’s not content to limit itself to astronomy. One of his other passions is traffic studies.
Connecticut, Upgren said, abolished tolls on its highways. The accident rate on those highways plunged, while it rose in other parts of the country. The reason is simple — changes in speed cause accidents, not speed itself. Toll gates cause dramatic changes — from full speed to stop.
On the far side of the toll booths, cars accelerate hard, jockeying for position. Again, speed changes lead to accidents.
Toll stations are therefore “high accident locations.”
Every city has some “high accident locations.” Usually, a few intersections account for 80 per cent of that area\’s accidents.
“It is a statistical impossibility,” Upgren asserted, “that all the poor drivers in the city just happen to congregate at those locations!”
Minnesota tried to draw attention to these so-called dangerous intersections. They put up a warning sign put up every time there was an accident.
"It was pretty disconcerting," Upgren commented, "to come to one intersection and see this forest of accident signs, and then drive for another ten miles and see nothing."
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The problem was not the drivers; the problem was the intersection itself.
Merely installing traffic lights doesn\’t solve such problems. The more traffic lights that drivers have to contend with, the more likely they are to try to run a light before it changes.
The same with stop signs and warnings. Past a certain point, Upgren explained, extra signage simply increases irritation and encourages violation of the law.
A number of reports recently have shown that reducing the forest of signs at some intersections actually improves safety. Left to themselves, the reports suggest, most drivers can and do assess risks, and act accordingly.
Poor road design doesn\’t show up in accident statistics, because it is rarely an option on most police reports. They have limited choices: impaired driving, negligence, weather conditions, speeding…
Whenever any location seems to have a surplus of accidents, there\’s a strong likelihood that faulty road design is a contributing factor.
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Copyright © 2007 by Jim Taylor. Non-profit use in congregations and study groups permitted; all other rights reserved.
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