Your browser is no longer supported

For the best possible experience using our website we recommend you upgrade to a newer version or another browser.

Your browser appears to have cookies disabled. For the best experience of this website, please enable cookies in your browser

We'll assume we have your consent to use cookies, for example so you won't need to log in each time you visit our site.
Learn more

How it works


When the early signs of congestion are detected on the M42 Active Trafc Management scheme, the control centre operator and automatic system will change the signs and signals to alert road users to the conditions ahead.

The system automatically calculates the best speed to keep the trafc owing and then this is displayed on the speed limit signals overhead.

The control centre can also open the hard shoulder as an extra running lane to reduce the impact of congestion by providing extra space for the trafc. This will help to keep the trafc owing and minimise delays.

'Theoretically a three-lane motorway reaches capacity at around 5,400 vehicles per hour, ' says Grant. Very roughly speaking, when we get to 5,000 vehicles per hour a light comes on in the control centre saying we are getting near to capacity. The variable speed limit signs are automatic, the hard shoulder is manual.' Before the hard shoulder is opened, a series of safety checks are performed. 'We do a debris sweep of the hard shoulder with a trafc ofcer and carry out visual checks. We also have sensors in the hard shoulder every 100m that detect the presence of vehicles. All of that takes place before we open it, ' says Grant.

Have your say

You must sign in to make a comment

Please remember that the submission of any material is governed by our Terms and Conditions and by submitting material you confirm your agreement to these Terms and Conditions. Please note comments made online may also be published in the print edition of New Civil Engineer. Links may be included in your comments but HTML is not permitted.