Lady Godiva wrote:Police_Driver wrote:They are not the numbers I will need nor care about when I anticipate any vehicle emerging from a junction, a vehicle speeding up as I overtake or when on blue lights the 3 vehicles in front of me indicating left to allow me to pass!
Dear Mr police Driver - with all due respect, can I suggest that they actually ARE the numbers you need, and I am a little perturbed that you suggest you do not care about them.
I wonder if what you actually mean is that you do not believe you need to consciously consider them as numbers. Well that is a different matter. However, if you are overtaking at a certain speed that dictates you need x-distance to complete it safely, then you definitely NEED to know that distance, even if you have got to know it through trial and error. You need to know it, and you need to care about it.
I think I understand what you're saying - some mathematical formulae dictate that to overtake a vehicle travelling at A mph from xM behind it (contact/overtaking position) whilst your vehicle is travelling at (A+10) mph and pull in yM ahead of it (ignoring acceleration and a non-straight path to make it simpler) requires a certain distance.
Add to this a safety factor for fast oncomers and you get a bigger distance.
Now, in a practical overtake, it's possible that you could modify the safety factor, based on training, experience and other skills, and thus reduce the overall distance.
Or increase the speed differential (but I was trying to examine a legal overtake) - Doug Holland wrote a 10 mph diff. required 12 seconds to complete the overtake.
20 mph needs 6s
30 mph needs 4s
I know I'm "shy" on overtaking and miss loads of opportunities.
An interesting observation in theoretical terms (as it would be illegal....) might be that if you overtook at 70 in an NSL (the target doing 50), you'd take half the time, half the distance and be twice as safe?