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Source: Robert Stokes, 785-532-1595, drbobb@k-state.edu
News release prepared by: Tyler Sharp, 785-532-2535, media@k-state.edu

Thursday, June 30, 2011

DRIVE 75: NEW SPEED LIMITS UNLIKELY TO CHANGE MUCH ON KANSAS FREEWAYS, EXPERT SAYS

MANHATTAN -- Drivers in Kansas will experience few differences when the state's speed limits increase July 1, according to a Kansas State University transportation expert.

Bobb Stokes, director of the University Transportation Center and professor of civil engineering, believes travel on the 807 miles of Interstates and freeways in the state that will allow speeds of 75 mph will be relatively unchanged.

"I don't think you will see much of a difference," Stokes said. "A 5-mph increase is really not a major increase."

If experiences in neighboring states are any indication, the higher speed limit should not pose a significant safety problem, Stokes said. Several states, including Oklahoma, Colorado and Texas, have speed limits higher than 70 mph. Also, highway fatalities are at their lowest rates nationwide in 60 years. Stokes credits this to increased seat belt usage, movements to discourage distracted driving, better transportation and traffic engineering, and safer automobiles. He also said the freeway-type facilities of each stretch of road designed for increased speed limits are designed to safely handle the higher speeds.

"All highways that have been designated for this change can handle it," Stokes said. "They are all very flat highways in terms of vertical and horizontal alignment; there are no at-grade intersections."

The highways follow a design control called design speed, Stokes said. Design speed differs from speed limits in that a nominal design speed allows for safe negotiation of the roadway at that design speed. Flatter curves and longer sight distances characterize highways with higher design speeds. That means it won't be 75 mph on Interstate 70 throughout the state. For example, certain sections of the Interstate in downtown Topeka were not designed to accommodate Interstate design speeds, so the speed limits along these sections will remain unchanged.

"These sections violate what drivers are used to and come to expect," Stokes said. "I suspect this was one of the reasons they probably didn't raise the speed limits there."

That means drivers on the various roadways, particularly Interstate 70 through Topeka, must adjust to the nonuniform speeds. Interstate 70 will have a speed limit of 75 mph from the Colorado border to immediately west of Topeka. Stokes said this runs counter to a guiding principle of highway design: driver expectancy.

"Drivers expect consistency and uniformity in the design features of the roadway as well as the regulations," he said. "By having some short sections of I-70 that are 70 mph instead of 75 mph, some people may assume that the 75 mph speed limit applies to all Interstate highways."

Future speed limit increases are unlikely for now, according to Stokes. Higher speed limits also evoke worries about the effects of increased speeding. Stokes believes most drivers will continue to travel at speeds they deem safe.

"I think most people will continue to drive at speeds they think are safe and reasonable and comfortable for the prevailing conditions," Stokes said. "Given the types of roadways that are going to have these types of speed limits, the higher design type of facilities, the higher speeds can be accommodated safely."