ST. LOUIS -Contractor crews will be working on the shoulder of Interstate 255 and Interstate 270, starting this morning, to install 68 digital speed limit signs along the roadway as part of a plan to implement variable speed limits along the interstate. Crews will close lanes on either the shoulder or the median around the crew installing the sign.

The first sign will be installed, starting at about 9 a.m. today, on eastbound I-255 just before the Telegraph Road overpass. Speed limits will remain on I-270 at 60 mph until MoDOT has completed the installation process sometime in early May.

By varying the speed limits, the Missouri Department of Transportation intends to help keep traffic flowing better along the interstate during periods of peak congestion.

Variable speed limits are used in Europe and on roads in New Jersey, Tennessee, Delaware and Washington State. If travel times are longer (because of congestion, or because vehicles are traveling slowly), MoDOT will lower the speed limit. If travel times are shorter, MoDOT will raise the speed limit.  Because of safety, however, the limits will not change significantly - speed limits could go as low as 40 mph during congestion and will remain at 60 mph during normal traffic flow.

Varying the speed limit will help control the flow of traffic into and through congested areas. A variable speed limit will help slow traffic approaching the congestion, which will reduce the congestion's duration. Traffic studies show that if traffic moves at a slow and steady pace, more people can travel through the congested area quicker.

Another benefit to variable speed limits is safety - if drivers follow the posted speed limits, they will have more time to react to congestion on the road ahead and will be able to slow or stop, if necessary, sooner. This will prevent many of the rear-end collisions prevalent during congestion.

The variable speed limit signs will be monitored and controlled by traffic operations experts in the MoDOT Transportation Management Center in Chesterfield.  MoDOT's current traffic control network of cameras and sensors will monitor the flow of traffic on the roadway and will notify operators when traffic speeds achieve certain conditions to raise or lower the speed limits. The operator will make the determination and then instruct the system to raise or lower the limits along the route.

"Variable speed limits will work along I-270, if the driving public doesn't exceed the posted speed limit," said Tom Blair, Assistant District Engineer in St. Louis. "Drivers in St. Louis have shown that they can adjust, as needed, to keep traffic flowing safer and smoother - MoDOT believes drivers will see the impact of variable speed limits to help minimize the impacts of congestion.

"Some drivers have expressed concerns that these variable speed limits will be used as speed traps - that isn't the case," he said. "We have more than 200,000 vehicles on I-270.  This effort will help us manage that traffic better, and help minimize the congestion along the interstate."

More information, including a video demonstrating why variable speed limits work, is available at www.modot.org/stlouis/links/VariableSpeedLimits.htm