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Not a drive-by process to set speed limits

How is the speed limit computed for Interstate 5? Why is it lower through Medford?

— Charles S.

The Oregon Department of Transportation undertakes a much different process to set speed limits on interstates than it does for any other type of thoroughfare, said Gary Leaming, spokesman for the department.

ODOT considers a number of factors in the engineering study that informs the eventual decision to set the speed, Leaming said. Those include crash history, roadway geometry, traffic volumes, even the percentage of traffic made up by trucks.

“If the investigation recommends a different speed from existing, the speed limit is changed,” Leaming said. That change is enshrined in Oregon Administrative Rules through a public process.

Relevant factors for Medford’s 55 mph speed limit, he said, were the viaduct, heavy traffic between the two interchanges, and the composition of traffic.

It was always that way, he said, though in 2004, the Oregon Speed Zone Review Panel looked at the possibility of raising the speed limit.

The panel considered raising the speed limit from 55 to 60 mph not only in Medford, but on sections in Portland and Eugene, as well.

A copy of the report shows the rationality of the panel’s approach to setting the limits; at one point, it acknowledges that “drivers must feel that the posted speed limit is reasonable; otherwise, they will tend to ignore the limit.”

The Engineering Investigation Report reviewed by the panel included an option to increase the speed limit in 5-mph increments, but ultimately, the panel recommended to keep the 55 mph zone, saying the increments were too short and “may present enforcement problems.”

Send questions to “Since You Asked,” Mail Tribune Newsroom, P.O. Box 1108, Medford, OR 97501; by fax to 541-776-4376; or by email to youasked@rosebudmedia.com. We’re sorry, but the volume of questions received prevents us from answering all of them.