mike[F] wrote:
But it's impossible to set limits in such a way, as the appropriate speed for a situation varies from day-to-day, from hour-to-hour, and from second-to-second, depending on the conditions at the exact moment a driver is passing there, along with his/her vehicle's capabilities, etc.
But you're viewing a speed limit here as a target to aim for. If a speed limit is a true limit, i.e. the speed above which it is guaranteed your speed is inappropriate, then it is of no consequence that conditions vary, because if you have to reduce your speed to cater for conditions, your speed will still be below the speed limit, so you're still within the law.
mike[F] wrote:
As Peter says, if we were to set a limit such that anyone exceeding it would automatically be in danger, regardless of conditions, this limit would be far too high 95% of the time.
It would only be too high if it were seen as a target speed to aim for, rather than a limit. For example, you could have 3 speeds on each sign - a limit above which you are automatically prosecuted, e.g. 140mph on a motorway. A suggested speed that most people in an average car can safely drive at in average conditions, perhaps 80mph for a motorway. And a minimum speed below which you are automatically prosecuted if there is nothing obstructing you from going faster, perhaps 50mph on a motorway.
mike[F] wrote:
Anyone driving within the speed limit, be they on the phone, no hands on the wheel, having not slept for two days, is automatically seen as a safe driver; and anyone exceeding the speed limit by as much as 2mph, even when said speed is safe for the conditions, is a reckless, dangerous driver.
Not true - I'm sure many people are convicted of DWDC&A when driving below the speed limit. If speed limits were genuine limits, then exceeding the speed limit by 2mph wouldn't be a safe thing to do.