In this week's Motor Cycle News.

There is a 'safest' speed for any given stretch of road (called the "85th percentile" apparently). Go faster or slower, and risk of an accident is increased. Government guidlines say cameras should be set below the 85th percentile speed, which means if you're travelling at the safest speed, you will get done :eek:

Good article and serious research. Check it out on safespeed.org.uk Follow the MCN links.

Richard.

clicky

But the 85th percentile speed will vary between day, dusk, and night, dry, damp or wet, etc. Unless you can constantly vary the speed limit to account for all these factors then you have to assume the lowest common denominator. Similarly speed limits must be standardised over certain lengths of road to make them clear, therefore some will be lower than expected most of the time.

You must also consider the consequences of collision. The example in the article, of a village where most collisions would occur at 25mph and no injuries would result, requires less enforcement than the dual carriageway where accidents at 50mph have more serious consequences IMHO.

I am not at all pro camera, but just trying to add a few balancing points to what is a v. complicated topic.

SK, I don't see that road conditions alter the point of the article. If speed limits are set for the lowest common denominator in terms of conditions, if you accept the 85 percentile rule then the safest speed, albeit reduced, will still get you clobbered.

I also have trouble with the lowest common denominator concept, in that if this is how speed limits are set (and we have to assume so, because you will never get done for doing 29 in a 30, even in the worst conditions) then by definition it is safe to travel much faster when conditions are good.

Last year I asked why you never see speed traps out when the driving conditions are dangerous and a reply from a bobby on here said it was probably because they were too busy attending RTAs to be messing about with people breaking the speed limit!

More questions than answers... :(

Richard.

PS Thanks for the clicky :)

True with speed cameras, not true with a traffic cop!

At least with a traffic cop there is some degree of intelligence there to assess whether the driver is causing a danger to themseleves or others travelling at their current speed in the given conditions.