ST. LOUIS – (KMOX)  Attention motorists; Interstate 270/255,  one of the most congested roads in St. Louis is going high tech.  In an effort to improve traffic flow and warn motorists of slowed  traffic, variable advisory speeds will begin posting today.

“Starting today, the digital speed signs will display flashing advisory speeds whenever traffic ahead is slowed to between 55 mph and 10 mph,” said MoDOT Assistant District Engineer Tom Blair. “The purpose is to advise drivers of congestion ahead. You need to slow down, pay attention and prepare to reduce speed.”

In addition, the standard black on white signs with the posted enforceable speed limit on I-270 will be 60 mph, except in work zones.

When average speeds on I-270 are at the posted speed limit of 60 mph, the digital boards will be blank. As conditions change, the I-270 variable advisory speeds will adjust showing the advised speed in increments of 5 mph starting at 55 down to 10 mph depending on the congestion on the road.

Advisory speed limits are not enforceable. MoDOT’s message signs will also include information regarding the congestion or lane closures ahead and increased travel times.

“We are advising drivers of how fast or slow their vehicle should be moving in order to safely get to their destination, in the shortest amount of time,” said Blair. “The advisory speed signs are similar to the black on yellow advisory speed signs posted on curves and ramps. It is the suggested speed to safely travel that stretch of road.”

Variable advisory speeds are designed to pace the traffic leading up to recurring rush hour congestion or from congestion caused by closed lanes due to a crash or work zone. If drivers ignore the speeds and hurry to the point of the congestion, it actually creates more congestion and is slower to get through. If drivers obey the advisory speeds, the overall pace of traffic will get through the congested area more quickly.

“MoDOT’s Gateway Guide traffic system of 300 cameras and 400 speed sensors knows when and where traffic problems happen. The message signs and advisory speeds are designed to warn you so you can slow down and prepare for congestion and potential lane reductions,” Blair said.

Copyright KMOX

Below is a video explaining the changes and the theory behind variable advisory speeds.

The full report conducted by the Missouri University of Science and Technology with HDR and Heartland Market Research is available on MoDOT’s innovation
library at:



Leave a Reply

Please log in using one of these methods to post your comment:

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s

More From CBS St. Louis

Download The App

Listen Live