The Concept of Car Lengths
Discussion
A phrase I often see batted around is that of “car lengths”, usually when describing following distances or how far someone is looking ahead whilst they’re driving.
What confuses/concerns me is that often the number of car lengths described for say, following another car on the motorway is as little as three or four “car lengths”, which to me seems woefully inadequate.
Now if we assume the average car length is 5 metres for easy maths, then four car lengths is 20 metres. At 70mph, a 2 second gap is a lateral distance of 63 metres, or by this alternative metric, around 13 car lengths. So how on Earth are folk ending up with just three or four car lengths? That would be less than a 1 second gap…
Alternatively, could it be that some assume the term “car length” to also include the distance between vehicles, so for example if they’re looking “six car lengths ahead”, what they mean is that they’re looking as far as the sixth vehicle ahead, not just a 30m segment, beyond which is invisible to them.
It just confuses me somewhat, different folk seem to have a different interpretation of the term, and that’s before we even consider what the physical length of the average car is…
Personally I prefer to stick with a time-based gap measurement, it’s far easier to judge a gap by counting a couple of seconds than estimating lateral distances with your depth perception.
What confuses/concerns me is that often the number of car lengths described for say, following another car on the motorway is as little as three or four “car lengths”, which to me seems woefully inadequate.
Now if we assume the average car length is 5 metres for easy maths, then four car lengths is 20 metres. At 70mph, a 2 second gap is a lateral distance of 63 metres, or by this alternative metric, around 13 car lengths. So how on Earth are folk ending up with just three or four car lengths? That would be less than a 1 second gap…
Alternatively, could it be that some assume the term “car length” to also include the distance between vehicles, so for example if they’re looking “six car lengths ahead”, what they mean is that they’re looking as far as the sixth vehicle ahead, not just a 30m segment, beyond which is invisible to them.
It just confuses me somewhat, different folk seem to have a different interpretation of the term, and that’s before we even consider what the physical length of the average car is…
Personally I prefer to stick with a time-based gap measurement, it’s far easier to judge a gap by counting a couple of seconds than estimating lateral distances with your depth perception.
Muddle238 said:
A phrase I often see batted around is that of “car lengths”, usually when describing following distances or how far someone is looking ahead whilst they’re driving.
What confuses/concerns me is that often the number of car lengths described for say, following another car on the motorway is as little as three or four “car lengths”, which to me seems woefully inadequate.
Now if we assume the average car length is 5 metres for easy maths, then four car lengths is 20 metres. At 70mph, a 2 second gap is a lateral distance of 63 metres, or by this alternative metric, around 13 car lengths. So how on Earth are folk ending up with just three or four car lengths? That would be less than a 1 second gap…
I think that's correct, and people travel far too closely to the car in front, especially on the motorway. What confuses/concerns me is that often the number of car lengths described for say, following another car on the motorway is as little as three or four “car lengths”, which to me seems woefully inadequate.
Now if we assume the average car length is 5 metres for easy maths, then four car lengths is 20 metres. At 70mph, a 2 second gap is a lateral distance of 63 metres, or by this alternative metric, around 13 car lengths. So how on Earth are folk ending up with just three or four car lengths? That would be less than a 1 second gap…
Yes, use the two second gap (car passes a noticeable spot, count two seconds ‘only a fool breaks the two second rule’ spoken normal speed). For more relaxed driving, and certainly on twisty A roads, I use a three second distance, with that and forward observation, braking is rarely needed. Unless you overtake, you will only be one-second later at your destination.
Pica-Pica said:
Yes, use the two second gap (car passes a noticeable spot, count two seconds ‘only a fool breaks the two second rule’ spoken normal speed). For more relaxed driving, and certainly on twisty A roads, I use a three second distance, with that and forward observation, braking is rarely needed. Unless you overtake, you will only be one-second later at your destination.
Spot on. And as for the twisty A roads, use the vehicle in front as a pathfinder. If the brake lights come on in the corner, ask yourself why. It may be that he just went into the corner too fast, but it may also mean that there are other dangers lurking around the bend.Gassing Station | Advanced Driving | Top of Page | What's New | My Stuff