The electronic signs were activated last month for a testing period.
Starting Tuesday, PennDOT says the signs will be used to post speed limits based on real-time travel conditions.
The signs are designed to help improve traffic flow and cut down on crashes.
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The 72 digital signs will increase or decrease the posted speed based on traffic conditions. Roadway sensors and a complex software system work together to lower the speed limit when conditions warrant, in hopes of preventing brake tapping: the main cause of traffic jams.
State police will be watching for drivers who don't follow the signs.
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These signs are part of PennDOT's continuing plans to improve traffic flow along the busy Schuylkill. Shoulder flex lanes and ramp meters are planned for the future.
As for the variable speed limit signs, officials acknowledge it's up to drivers to obey the posted limit and resist the urge to hit the gas pedal to make the PennDOT plan work.