Drivers Have Need For A Certain Speed: 72 Mph Nationwide Study Finds Common Comfort Zone For Most Motorists

Higher speed limits across the rural West have not led to substantially higher speeds but instead allow more motorists to drive legally at speeds they tend to drive anyway, a Texas researcher says.

“State-to-state comparison of average speeds conclusively shows the human desire to travel between 72 and 73 mph regardless of the posted limit or lack thereof,” said Carl Fors, president of Speed Labs in Fort Worth, Texas.

The before-and-after comparison was made in Texas. There, Fors and his colleagues clocked 1,184 cars on a rural stretch of Interstate 10 when the speed limit was 65 mph, then 1,794 cars at the same place after the speed limit had been raised to 70 mph. Result: The average speed rose only 1.3 mph, from 71.4 to 72.7 mph.

Fors then broadened the study to see what motorists were doing on other rural highways through the West.

After training his laser on more than 24,000 cars, trucks and semitrailers in Montana, Colorado, South Dakota and Texas, Fors said, he didn’t just identify an average speed; he discovered a “human desire.”

The phrase is no accident. Fors calls it the “want and will” rate of travel - the speed at which the average driver both wants to, and will, move on down the road.

This observation, according to Fors, has significant consequences.

First, it suggests that legislatures that tinker with speed laws largely are wasting their time. The want-and-will speed of 72 to 73 mph will prevail.

But more importantly, Fors suggests, legislatures that accept this law of human nature and set their speed limits accordingly actually contribute to highway safety.

“Higher interstate limits reduce the percentage of speed variance,” Fors said. That is, more drivers will travel within 3 to 4 mph of one another with a 75 mph speed limit than they will if the speed limit is 65 mph.

That is safer because members of a convoy moving at the same speed are less likely to experience an accident, he said. The less passing going on, the better.

But if the posted speed is lower than the want-and-will, more drivers will have to dart around those motorists who try to obey posted limits even if it seems unnatural.

The reverse is also true, Fors said. If there is no posted limit, as in Montana, a significant number of throttle jockeys will rocket by the motorists doing what comes naturally, disturbing the want-and-will status quo.

“The percentage of drivers traveling in excess of 80 mph is consistent in all states (5-6 percent) except Montana,” where it ranged as high as 16 percent, he wrote. “This evidence strongly points to the necessity of some benchmark interstate speed limit in Montana.”

Fors recommended 75 mph as a new Montana speed limit. He said in states that now have a 75 mph limit, “the vast majority of drivers did not drive the limit.”

At the request of the Montana Highway Patrol, Fors also read license plates while he was measuring speed in the state. He said his research confirms anecdotal testimony that Montanans are not the main speedsters on Montana interstates.

“Out-of-state and Canadian drivers once reaching the ‘promised land of speed limitless’ Montana put their foot down,” Fors concluded. While Montanans averaged 73.1 mph, out-of-state motorists averaged 74.6 mph - and Canadian motorists averaged 77.5 mph. Twenty-six percent of Canadian drivers were clocked at greater than 80 mph.

Among the vehicles observed speeding in excess of 80 mph, Chevy Suburbans ranked No. 1, far ahead of the 10th-place BMW.