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Speed limits increasing on 3 highways in east Idaho


The following is a news release from the Idaho Transportation Department.

RIGBY – The posted speed limit on three state highways in eastern Idaho will increase beginning Monday (Aug. 1).

Crews will install 70-mph speed limit signs on U.S. 20 between Idaho Falls and Butte City, on Idaho 22 between its junction with Idaho 33 and Dubois, and on Idaho 28 between Mud Lake and Leadore. The increased speed limit is for both vehicle traffic and trucks.

U.S. 20: Between Idaho Falls and Butte City (milepost 252.51 to 301.19)
Idaho 22: Idaho 33 junction to Dubois (milepost 24.67 to 68.07)
Idaho 28: between Mud Lake and Leadore (milepost 15.15 to 89.49)

Along with this increase, the transition speed zone on Idaho 28 south of Leadore will be increased from 45 to 55 mph.

“The increases are appropriate for traffic safety and flow,” said District 6 Traffic Engineer Ben Burke. “However, posted speed limits cannot replace common sense. Drivers should always slow down if necessary to meet hazardous conditions.”

Current speed limits, which are the maximum speed motorists can legally travel under ideal roadway and weather conditions, remain in effect until the new signs are installed.

In 2014, the Idaho Legislature amended the “Basic Rule and Maximum Speed Limits” in Idaho Code to allow the Idaho Transportation Board to raise interstate speed limits to 80 mph and other state highway speed limits to 70 mph, when concluding that the increases are in the public interest based on engineering and traffic studies.

Idaho Transportation Department (ITD) officials completed studies of the three highways May 13, recommended the increases to the Idaho Transportation Board, and received approval June 16.

Studies indicate that the 85th-percentile speed of drivers on these routes is between 70 and 80 mph. The 85th-percentile speed is the speed 85 percent of motorists are driving at or below. Setting speed limits according to the 85th-percentile speed results in the lowest crash rates.

ITD officials also discussed the proposed speed limit increases with county officials and law enforcement prior to determining the changes.

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