Within two years, drivers along the Jane Addams Memorial Tollway may see a different speed limit posted every time the traffic flow changes.

Under a program called “active traffic management,” the Illinois Tollway Authority plans to turn the road into a “smart corridor” with overhead digital signs every half-mile. Staff monitoring the road 24/7 will use those signs to alert drivers of congestion or collisions ahead and to change the recommended speed limit or close lanes to move traffic along.

The changing speed limits are only advisory; motorists can’t be ticketed.

A red X would appear above a closed lane, and an accompanying text alert might indicate, for a example, a stalled car in the middle lane.

“We live in one of the most congested regions in the country, and we can’t keep building a lane every time congestion increases, …” said Kristi Lafleur, Illinois Tollway executive director said. “Information will be critical to drivers making smarter choices.”

The real-time alerts, endorsed this week by the Illinois Tollway Strategic Planning Committee, will appear on Interstate 90 from the Kennedy Expy. to Barrington Road, part of improvements that include the ongoing reconstruction and road-widening.

The plan also includes adding a “preferential shoulder” that will be used during busy travel times.

The digital signs would indicate whether the lane should be used by Pace buses or perhaps emergency vehicles. The signs could redirect regular traffic into the shoulder to avoid accidents and relieve congestion.

Active traffic management strategies started in Europe, but transportation departments have been rapidly installing them across the United States. More than 20 states use some of its elements, according to the Federal Highway Administration.

The state of Washington launched traffic management on Interstate 5 northbound to Seattle in 2010 in a way very similar to the Illinois plan.

Travis Phelps, spokesman for the Washington Department of Transportation, credits the signs there with lowering the number of weekday accidents by 7.5 percent and weekend accidents by up to 15 percent. Phelps said the signs help drivers make safe decisions and help move traffic more quickly.

“It works really well in the urban environment because it warns drivers of incidents up the road,” Phelps said.