What does ‘A’ and ‘B’ mean on the second line of the signs?
The letter on the second line of the signs is called the carriageway identifier. On the M25, this is either A or B if travelling on the main carriageway. This helps the emergency services identify which direction the road user is travelling along the route. For example: • “A” is the clockwise direction of the M25 main carriageway. • “B” is the anti-clockwise direction of the M25 main carriageway. If the driver location sign is on a slip road, the carriageway identifier will be H or K or L or M depending upon the location.
