Split speeds topic of university study

By David Tanner, Land Line associate editor | 6/4/2013

University researchers hope to answer the question once and for all about whether split speed limits between cars and heavy trucks make roads safer or less safe.

Wayne State University has embarked on what the recipients of a grant say will be the most comprehensive study of split speeds to date in an effort to help Michigan state officials make informed decisions about speed limits, including the possibility of raising truck and bus limits to the limit set for cars. Cars can currently go 70 mph in Michigan, while heavy trucks and buses are limited to 60 mph.

Researchers will collect and crunch data from Ohio, Indiana and Michigan, three states that share some roadways but have different views about speed-limit differentials among cars and heavy trucks.

“We’re comparing three scenarios,” associate professor of civil and environmental engineering Peter Savolainen said in a press release. “One is to maintain Michigan’s current policy, which establishes a speed limit that is 10 mph lower for trucks and buses. A second alternative is to decrease the speed limit difference from 10 mph to 5 mph, and the third is to make a uniform speed limit for all vehicles.”

A number of studies have found that uniform speeds among cars and trucks are the safest – a point that OOIDA has made in comments on various rulemakings, including heavy vehicle speed limiters – but not every group or lawmaker is convinced.

The Wayne State study, titled Evaluating Differential and Non-Differential Freeway Truck and Bus Speed Limits, will review crash data involving trucks and buses, but will attempt to go deeper to evaluate delays, pavement quality, air quality and the effects on freight movement.

The Michigan Department of Transportation is funding the study with a $175,000 grant to Wayne State’s College of Engineering. Wayne State is based in Detroit.

“By carefully examining the impacts of speed limits from various aspects, we’re hoping to produce sound evidence that will lead to an informed decision as to Michigan’s future freeway speed limit policy,” Savolainen said.

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