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Smart motorway signs

Reported via mobile in the Sign issue (NH) category anonymously at 12:08, Mon 27 March 2023

Sent to National Highways less than a minute later. FixMyStreet ref: 4363529.

Always after M27 junction 5 the 4 lane smart motorway signs went from 60 to 50 to 60 then 70 why does it do this? there is no debri on motorway, no stranded vehicle. Same as last week popped up flashed a sign briefly, then went away, then suddenly popped up again, saying 40MPH right next to cameras going east bound and to see how many cars slammed on their brakes and glad nobody had an accident. All because the motorway sign just keep flashing up for no reason. It's starting to get a bit scary driving on smart motorway when signs just appear out the blue like this.

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  • National Highways may implement signals and reduced speed limits for a variety of reasons, to ensure the safety of the travelling public, our workforce and emergency responders. They will not be cleared until it’s been established that it’s safe to do so.

    Speed limits can also be set automatically in real time by a system known as MIDAS (Motorway Incident Detection and Automated Signalling), which uses loop detectors in the carriageway that collect real time data such as traffic count, speed and density. Signal gantries automatically display speed limits in response to the data recorded by the loop detectors. MIDAS detects when congestion is starting to build up. The settings in this system are tuned to match the traffic patterns, to ensure that reduced speed limits are set in time to prevent or reduce congestion without being set too early. Initially, 60mph signals are displayed on the gantries and then as the traffic demand increases further, 50mph signals are displayed. This provides an extra element of control at a slightly lower speed, allowing traffic to flow more smoothly and gives minor congestion a chance to disperse before further congestion can form. The system helps to minimise the risk of accidents and produce more reliable journey times.

    Drivers who are close to the signal are not expected to brake suddenly when the speed limit is reduced, but rather to slow down so that they are within the limit as soon as it is safe to do so. When the speed limit has increased, the lower speed limit can no longer be enforced at that signal, and this is built into the design of the cameras.

    State changed to: Closed

    Posted by National Highways at 14:29, Wed 29 March 2023

This report is now closed to updates from the public. You can make a new report in the same location.