Following Distance on dual carriageways:
You should normally stay about a 3 second gap behind the car in front, further if you have someone close behind you, or if the road is wet. Above 40mph you are too close if you can read the number plate of the car in front.
The biggest cause of accidents is driving too close behind another vehicle. You can't hit something if you're not close to it! A lot of drivers tailgate regularly, just because they don't realise how dangerous it is, and how long it takes to stop. Being able to see past the car in front, to see what's happening up ahead, doesn't help if the car in front brakes hard for no apparent reason (as learner drivers do sometimes!).
The Highway Code and advanced driving institutions advocate keeping two seconds away from the car in front (in dry conditions - double in the wet):
"Only a fool breaks the 2 second rule. "
However as far as we are concerned this is only adequate at speeds below 40mph, above 40mph it should be at least 3 seconds: To put this into practice wait until the car in front passes a marker, such as a signpost, then it should be 3 seconds before you get to the same marker.
On dual carriageways, and motorways, there are small blue and yellow posts every one hundred yards - this equates to your overall stopping distance at 70 mph (photo above).
The UK Highway Code quotes a 0.7 second reaction time before braking. Some countries state that up to 4 seconds is usual for the average driver, who is possibly only partially concentrating. Reaction time is not 1.5 secs
How speed can kill, and keeping a safe distance back can keep you safe:
Imagine you are travelling along a fast dual-carriageway at 70mph. At a certain point in time a car is overtaking you at 100mph. You are both alongside each other for a moment. At that moment a car in front hits the crash barrier and bounces back towards you .
You, and the car next to you, go for the brakes. You manage to stop just in time in 315ft (Highway Code stopping distance at 70mph). The car that was next to you hits the obstruction at over 70mph ( stopping distance at 100mph of 600ft).
These figures actually work out - I didn't believe it until I calculated it myself - Food for thought !