Speed Management in Norfolk
We all value our own time, so when we are travelling we value speed in order to reduce travel time; however this must be balanced against the safety of ourselves and others.
National and international research has clearly identified that the faster that traffic moves on average, the more accidents there are. On every class of road, both the risk of accidents and the severity of accidents rise markedly as average traffic speeds increase.
The physics involved is simple: a faster vehicle travels further during the driver’s reaction time; the additional energy (proportionate to the square of its speed) takes longer for the brakes to dissipate; in the event of a collision the residual energy must be absorbed in the crash.
- At 30mph, vehicles travel 13 metres/44 feet (about three car lengths) every second.
- Even in good conditions, the difference in stopping distance between 30mph and 35mph is an extra 6 metres/21 feet.
- At 35mph a driver is twice as likely to kill a pedestrian as they are at 30mph.
The unprotected human body has limited ability to withstand a collision; the risk of death or serious injury to pedestrians rises very abruptly at impact speeds over 20mph. The occupants of a modern car however, are generally well protected up to impact speeds of 40mph. So a speed that can feel safe and comfortable to one road user can impose unacceptable risk and concern to another.
But accident frequency also rises with the variance in vehicle speeds. In other words the larger the spread of speeds around the average speed, the more accidents there are. At 25 per cent above the average speed, a driver is about six times more likely to have an accident than a driver travelling at the average speed. Speed variance has been found to increase with the difference between posted speed limit and the ‘design speed’ of the road. This can cause a problem if unrealistically low limits are imposed on high standard roads.
So the key to successful speed management is achieving traffic speeds appropriate to the environment and conditions, with as little variance between the slowest and fastest vehicles as possible.
- For more information on organisations and projects that help to reduce collisions caused by the misuse of speed please click here.
- For more information on speed management measures please click here.
- For more information on speed limits please click here.
