This article is incomplete. Check back in late November.

Smart motorways were designed to be the future of Britain’s road network. Instead of spending significant amounts of money on widening motorways, engineers could increase capacity whilst leveraging existing infrastructure using technology. This would allow them to vary speed limits, manage congestion, and even open the hard shoulder during periods of heavy traffic. The principle was sound: squeezing as much capacity out of existing carriageways as possible.

Though after almost twenty years of operation, smart motorways are thought to be unsafe and unfit for purpose. High-profile accidents, delayed safety measures, and patchy technology have left the public questioning whether the risks are worth it.

The Concept

Smart motorways are based on two principles: dynamic speed management and flexible carriageway use.

Dynamic speed management is enabled through the use of screens suspended from gantries. Variable speed limits are typically set at 40, 50, or 60 mph, with 70 mph applying when no restriction is displayed. Information signs are also placed regularly along the carriageway, which are usually used to warn drivers of closures and delays. In theory, this flexibility should improve safety as well as capacity, by slowing traffic before incidents and keeping vehicles moving steadily. It also allows for the reduction in noise at certain times by reducing the speed limit. This is done during school hours on certain parts of the network.

Flexible carriageway use allows for the implementation of dynamic hard shoulder (DHS) and all-lane running (ALR) motorways. With DHS, the hard shoulder becomes an active traffic lane during periods where high traffic is anticipated. ALR goes further, permanently converting the hard shoulder into a live lane

Technology underpins smart motorways. Stopped Vehicle Detection (SVD) systems, as the name implies, use radar to identify stationary vehicles. These are designed to alert control room staff, who could then close affected lanes.

Data collected from cameras and sensors is also fed into the National Traffic Information Service (NTIS), which provides real-time information to traffic management systems and navigation apps, helping to keep travel time estimates accurate.

So where did smart motorways go wrong?

The Implementation