ST. LOUIS - The Missouri Department of Transportation will be implementing variable speed limits along Interstate 270 starting Thursday, May 22, 2008.

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.

To help drivers anticipate and respond to the speed limit changes along I-270, MoDOT has implemented the following procedures for the variable signs:  1) Speed limits will change in five mile per hour increments; 2) Once the speed limit in an area changes, it will not change again for at least five minutes. 3) When the speed limit changes on a sign, the sign will flash for at least five seconds, indicating that the speed limit just changed.

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.

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

###

Media note: MoDOT officials will be available for interviews during Thursday morning's commute.  Please call Andrew Gates at 314-340-4161 before 4 p.m. on Wednesday  to make arrangements for interviews.