Safety in Numbers

| May 29, 2007

Combining differential speeds, basic physics and a wealth of truck crash data results in a mixed message about the wisdom of governing truck speed.

Common sense tells us that the faster vehicles move, the more likely they are to wreck. The greater the speed of a wreck, the worse it will be. Common sense also tells us that vehicles moving together at varying speeds are more likely to wreck than those moving at virtually the same speed.

Which point is more important when it comes to governing truck speed? Regulators now face that question and others as they weigh the merits of truck governing petitions submitted by the American Trucking Associations and Road Safe America.

“Information about the kind of precise effect of speed on crash rates, at the level of resolution needed, is not currently available,” says Dan Blower, a researcher at the University of Michigan’s Transportation Research Institute. He served as a consultant on one of the most important truck safety studies to date, the Large-Truck Crash Causation Study, a project of the Federal Motor Carrier Safety Administration and the National Highway Transportation Safety Administration, released in March 2006.

The Truckload Carriers Association considers the data so inadequate that it opposes the petitions. In its comments, TCA says, “While ATA and Road Safe America have determined that speeds greater than 68 mph are unsafe and detrimental to the motoring public, neither have been able to justify why 68 mph is the barrier at which unsafe speed is obtained.”

For some safety proponents, including Road Safe America co-founder Steven Owings, crash data pales in comparison to the physics of a truck at high speed. Because it’s “the biggest, by far most dangerous vehicle on the road, that can’t see as well as smaller vehicles, can’t maneuver as well as smaller vehicles, and mostly importantly can’t stop anywhere near the same distance as smaller vehicles,” it should be kept to slower speeds, he says.

Following is an analysis of some key speed statistics.

GENERAL SPEED DATA
Speeding nearly triples the odds of being involved in a crash.
- AAA Foundation for Traffic Safety

Speeding is a factor in 30 percent of all fatal crashes.
- National Highway Transportation Safety Administration

As opponents of governing note, much of the speed-related crash data is too broad to determine the effectiveness of governing trucks. “Speeding” can be 40 mph in a 30 mph zone, for example. “Too fast for conditions,” a common accident factor, includes driving on wet highways, around tight curves and through construction zones, at speeds that could be high or low, legal or not.

Nevertheless, certain basics about speed can’t be ignored, argue low-speed proponents. On its website, the Insurance Institute for Highway Safety notes that speed increases both the severity and the risk of having accidents in three ways: It reduces driver response time; it increases stopping distance; it increases crash energy exponentially (a 50 percent increase in speed increases energy by 125 percent).

Beyond that, the effect of tinkering with speed limits isn’t always clear. Look, for example, at what happened as Interstate speed limits changed in recent decades.

By March 1974, all states had adopted a 55 mph speed limit, following federal highway funding pressure in response to the oil crisis. “The National Research Council attributed 4,000 fewer fatalities to the decreased speeds in 1974, compared with 1973,” says IIHS.

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