If a lower speed limit is displayed on a smart motorway, you should reduce your speed and obey the displayed limit. A speed limit shown inside a red circle on an overhead or roadside signal is mandatory, so you must not exceed it.
Variable speed limits may be used to manage traffic flow, reduce congestion or respond to an incident or hazard ahead. Reduce your speed smoothly and safely rather than braking sharply at the last moment, and continue to obey the displayed limit until signs indicate that it has changed or the national speed limit applies again.
Quick Self-Test
A smart motorway signal displays 50 inside a red circle. What should you do?
A) Continue at 70 mph if the road is clear
B) Slow down only if you see congestion
C) Reduce your speed and do not exceed 50 mph
D) Treat the limit as advisory