September 27, 2021
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The Idaho Transportation Department is using variable speed limit technology within an Interstate 84 work zone in Canyon County as a way to enhance safety for its work crews and motorists alike.

[Above graphic via the ITD]

Typically, ITD said it reduces work zone speeds to 55 mph or 45 mph depending on the type of roadway construction activity involved. However, variable speed limit technology allows the agency to make “responsive adjustments” to speed limits, raising them back to 65 mph, for example, when construction crews are not in the work zone or when safety barricades are in place.

That promotes greater travel efficiency without sacrificing safety on interstates, ITD noted.

Conversely, flashing beacons help provide early warning to motorists ahead of the work zone when speed limits are reduced from 65 mph. The agency added that it expects to remove those variable speed limit signs once I-84 construction wraps up in the summer of 2023.

Shawna King

“This technology will allow us to keep traffic moving as efficiently as possible along this key corridor,” explained Shawna King, ITD design construction engineer, in a statement.

“Variable speed limits have a track record of enhancing safety in active work zones,” King added. “Implementing the variable speed limits allows us to keep both crews and drivers safe while work is being done and then bring speeds back to normal when it is safe to do so.”

ITD noted that several other states are successfully using variable speed limit technology – particularly Washington and Utah – and research collected by the Federal Highway Administration shows such systems tend to improve driver compliance with posted speed limits.

This reduces crashes and improves safety for road crews and the motoring public, the agency stressed.

editor@aashto.org

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