Electronic monitoring systems and CCTV cameras constantly ‘watch’ smart motorways: the information and images are sent in real time to a control centre. When congestion or an accident develops, the control centre staff can take action, depending on the situation and the type of smart motorway affected.
For example, in times of busy traffic, the speed limit might be adjusted. This works by controlling the flow of traffic heading into the busiest areas, to reduce build-up and stop-start congestion and keep vehicles moving. The limits are shown on overhead gantries and are enforced by speed cameras. If a gantry doesn’t display a limit, then the national speed limit applies.
On a DHS motorway, the control centre might also open the hard shoulder to traffic to increase the number of usable lanes and make room for more vehicles. Gantry signs will advise whether the hard shoulder is open or closed.
ALR motorways have all lanes open by default, which means there’s no hard shoulder to pull over if you have a problem. The solution is to pull into a lay-by type of space known as an emergency refuge area (ERA) and call for assistance using the special telephone each one has. An ERA is placed at least every 1.5 miles and is indicated by large blue signs and orange road surfaces.
Sometimes the inside lane is closed on ALR motorways. This is done using signs on overhead gantries: you’ll see a big red X above the closed lane, which means you need to move to another lane as soon as you safely can.