Inspired by this thread, where the topic of following distance was brought up.
In this example, someone mentioned a common rule of thumb I’ve heard of - specifically, one car length per 10 miles per hour. Also mentioned in the thread was a rule of thumb based on what you can see of the car behind you vs type of road you are on - see the grill of the car behind you on a small road, the license plate on a larger one, and tires on the highway.
I’m sure there are a bunch of other ways people use to judge following distance, but they all seem overly complicated and open to interpretation (such as the obvious: a car length - well, what kind of car!?)
I’m curious what ways people learned to judge following distance. When I took drivers ed (about 18 years ago), we learned based on the Smith System, and I was taught to follow 2 seconds behind the car in front. Apparently this has been updated recently to 4 seconds, but the same idea still stands - follow behind the car in front based on how many seconds it takes you to reach a spot where the person in front of you passed.
It seems to me that this is a far simpler method of judging following distance. As speeds increase from a rural road to a highway, the distance automatically increases as well. No judging car lengths (which requires mental chopping of a distance into pieces), no rules based on factors that may change from one type of car to another (car length, position of license plate, vehicles height above the ground, etc). Simply start counting when you see a car in front of you pass something prominent (telephone pole, end of a guard rail, a particular hash line), and see what number you are at when you pass the same mark.
I learned the “three second rule” when I took driver’s ed 28 years ago. Obviously speed and driving conditions play a major factor in the equation, but I still think that’s a good rule of thumb to start from.
One car length per 10 mph isn’t nearly enough on a freeway. My kids just both took drivers ed from 2 different places, and they were taught AT LEAST 3 seconds (4 being even better). I was taught the same thing ages ago). It makes much more sense to set your following distance by seconds than car lengths if you think about how long it takes you to stop - a second to react, then a couple seconds to do your response (which is why 4 seconds would be even better).
When I was taught in the 60s, it was a car length for every ten mph. I didn’t hear the three second rule until the 80s, but it clearly makes much more sense. Much easier to judge time than what is considered a car length.
I don’t remember what I learned from my father or from driver’s ed. It was probably the car length rule. But long before I started driving, I saw a commercial that endorsed the 2 second rule, and that made perfect sense to me. That’s what I’ve always used.
In driver’s ed they taught us to say “turvallisuusväli” (translates to “safe distance”) to gauge the distance, if the car in front passes an object and you haven’t reached that by the time you’re done saying it… you’re far enough.
Regardless of whatever the correct distance is, when the rubber hits the road the actual distance used will be ‘close enough so that cars travelling in adjacent lanes can’t cut in’. This is probably less than 1 second.
On I-75 in Georgia, following distance is frequently one car length between cars at 80+ mph. For twenty cars in a row-
People lose their licenses for that in Germany.
I look at the vehicle ahead. In the context (road, weather, etc.), what would happen if they suddenly slammed on their brakes? If I don’t like the answer (such as “my truck will crush their soft bodies”), I ease off.
I learned 2 seconds for normal driving conditions, 4 seconds or more for wet/slick conditions. We weren’t taught any difference between highway and city traffic.
Anyhow, that’s what we were taught. Given an open highway, I like to keep 3-4 seconds back. However, in normal Chicago-area highway driving conditions, it’s pretty much impossible to even keep to the two second rule, as the instant you open up a two-second gap, somebody takes it. And then you back off to get another two seconds, and somebody takes that. Ad infinitum.
I also (in 1992 Driver’s Ed) learned the two second rule. When the car in front of you passes something (a road sign, a crack in the pavement, etc.) with his rear bumper, you count two seconds, and your front end should be at or behind that same spot.
I did hear someone at some point mention that “now” it was 3 seconds, but that was a while ago. Hadn’t heard They’ve bumped it to 4.
According to this cite, that ratio actually seems to hold really well, in terms of pure breaking distance (not taking into account reaction time).
The only thing I’d amend is that unless the car in front stops dead in its tracks, it will still be progressing forward if they slam on the brakes, which lowers the absolute closing distance and speed between your vehicle and the one in front.
However, that is a bit of a nitpick for the rule of thumb, because it seems like 3-4 seconds on the highway is pretty common, and makes sense.
I learned the three second rule sometime during my early years. Peter Brock used to have an ad campaign about following distances and overtaking technique. The main point about overtaking being to hang back a bit rather than tail-gate because you can see more of the road and you can accelerate up behind the car then pull out and complete the manoeuvre more quickly.
On some stretches of motorway in the UK they have big chevrons painted on the road. If you always have one chevron visible between you and the car in front you will be ok (for 70mph, I guess). It does seem to work quite well.
The M25 (London ring road), however, is an 80 mph traffic jam with about 1/2 a car length between vehicles. It’s a fucking nightmare.