You MUST NOT exceed the maximum speed limits for the road and for your vehicle (see the speed limits table). The presence of street lights generally means that there is a 30 mph (48 km/h) speed limit unless otherwise specified.
The speed limit is the absolute maximum and does not mean it is safe to drive at that speed irrespective of conditions. Driving at speeds too fast for the road and traffic conditions is dangerous. You should always reduce your speed when
- the road layout or condition presents hazards, such as bends
- sharing the road with pedestrians, cyclists and horse riders, particularly children, and motorcyclists
- weather conditions make it safer to do so
- driving at night as it is more difficult to see other road users.
Stopping Distances. Drive at a speed that will allow you to stop well within the distance you can see to be clear. You should
- leave enough space between you and the vehicle in front so that you can pull up safely if it suddenly slows down or stops. The safe rule is never to get closer than the overall stopping distance (see Typical Stopping Distances diagram, shown above)
- allow at least a two-second gap between you and the vehicle in front on roads carrying faster-moving traffic and in tunnels where visibility is reduced. The gap should be at least doubled on wet roads and increased still further on icy roads
- remember, large vehicles and motorcycles need a greater distance to stop. If driving a large vehicle in a tunnel, you should allow a four-second gap between you and the vehicle in front.
If you have to stop in a tunnel, leave at least a 5-metre gap between you and the vehicle in front.
Rule 126: Use a fixed point to help measure a two-second gap
The Highway Code © Crown copyright. Source: http://gov.uk/highway-code