There are three main types of smart motorway:

Controlled

This type of smart motorway has mandatory speed limits with a hard shoulder available for emergencies only.

Hard Shoulder Running

The hard shoulder can be opened during busy, peak times on the motorway when needed, reducing congestion.

All lane running schemes

This type of smart motorway opens all lanes for traffic to use including a former hard shoulder and makes use of variable speed limits.

Only in the event of an incident is the hard shoulder lane closed to traffic.

A lane closure is indicated by a big red X on the gantry overhead. This means that, if you are already in lane 1 (the hard shoulder), you must exit it as soon as possible, as it indicates an obstruction in that lane. Ignoring the X sign can be extremely dangerous and will bag you a fine and points on your license.

Speed limits on smart motorways actually change depending on the traffic conditions, the variation is designed to act as a calming measure. The gantry overhead displays the current speed limit for a lane and if there is no speed limit displayed, then the national speed limit applies. Speed limits are enforced by speed cameras.

Should drivers break down or be involved in an accident, there are emergency refuge areas (ERAs) at the side of the carriageway to use. These are clearly marked by blue signs as in the image below with orange SOS telephone symbols and are spaced at roughly 1.5 miles apart.