Ok, I don’t want to start a debate on whether or not it is polite, good or evil to stop a couple car lengths behind at a stop light. However, the reason often given is it protects them if they are rear-ended.
But wouldn’t a 2 car length gap allow your car to be pushed sideways into oncoming traffic?
Also wouldn’t that larger gap just allow you to build up speed to hit harder? I mean, if you are 2’ behind the car in front, you can’t build up any speed after being rammed.
So, what’s the actual physics, safety-wise? BIG or small gap?
Having been rearended, I was happy to have left about a half a car’s length between me and the car stopped in front of me. With a ~10 mph collision, that was just enough space to allow me to stop my vehicle, as well the maniac who hit me, without bashing another car.
The energy’s got to go somewhere. With a gap, that energy can be put into the brakes as heat. With a smaller gap, more of the energy will go into crumpling the car, and less into friction in the brakes.
I’m not sure I understand how more space would allow a car to be pushed sideways into oncoming traffic.
Discussing car lengths in term of traffic safety is a huge fallacy. For cars in motion, a spread of 2 seconds to get to the next car’s position is much more relevant to safety and accommodates all traffic speeds. I have never heard of cars staying back 2 car lengths at traffic lights in my 20 years of driving.
With the prevalence of sensor operated traffic signals, leaving excessive space (more than a car length) between vehicles may impede the smooth flow of traffic. The sensors will often initiate a change in the signal if they do not detect a vehicle within 2 to 3 seconds. Leaving an abnormally large gap and then being a bit slow to respond when traffic begins to move, may cause the signal to change prematurely and subsequently cause more of a backup behind the offending vehicle. I see this quite often.
Being rear ended is a fairly rare occurence and the added safety of leaving added space between vehicles is debatable and I personally think it’s not a worthy habit, better to consider the plight of the drivers behind you and close the gap to a few feet.
Good grief! Is that why people do that? I always thought it was because people had a depth-perception problem or something.
Is there a similar explanation for why, when the light turns green, people wait until the car in front of them is nearly to the horizon before they lazily tap their accelerator?
Good grief! Is that why people do that? I always thought it was because some people have depth-perception problems or something.
Is there a similar explanation for why, when the light turns green, people wait until the car in front of them is nearly to the horizon before they lazily tap their accelerators?
If there is no signficant space,you must hit the car in front. But if there is quite a bit of space, another car hitting you from behind* but at an angle* could spin you left, into oncoming traffic.
Actually, this touches on another good reason to leave a gap. When the light turns green, you can immediately release your brakes and start your car rolling, if you have a fair distance between you and the car ahead. If you were inches off your predecessor’s bumper, you’d waste precious seconds waiting for him to get far enough ahead of you for safety before you could start moving.
It is with some people. I’ve been driven home by a workmate who will do it when she’s the first car at the lights. From the passenger seat, I can see the white stop line on the road in front of the hood, we’re that far back. Her front bumper would be lucky to be six inches forward of the rear bumper of the guy next to us. I’ve told her to go a little bit forward…
six inches
“OK?”
“No, more more!”
a foot
“No, go a LOT more forward!!”
Another foot.
“OK, now?”
Eugh.
And when the lights go green, she is s.o.o.o.o f.u.c.k.i.n.g slow to take off.
When we leave work, we have to join a major six lane road from a tiny one-lane dead end. The lights allow only about three cars through before we get another five minutes of red. Maybe four or five cars if you have a lot of guys who are familiar with that place, and drive a little aggressively to help each other out (ie. right there on the clutch, nose across the line a fraction of a second before the green). But if this lady is there at the line, she gets through and her alone. I’ve been with her when she’s done it. She actually clips the red by the time she’s through the intersection.
You learn in various sundry places to leave gaps when stopped so if something happens you can jet instead of being so close that you have nowhere to go. For me it’s almost a habit, but I don’t lay back two car lengths, more like a couple of feet so I have clearance.
The reason most people I know keep some distance from the car in front of them is to have an escape route for car-jackings and that sort of thing. But I grew up close to neighborhoods where people think of these things. Two car lengths is a bit excessive, though.
Yeah, and my aunt could have been my uncle if she just had the balls. There is no logical reason for leaving a car length, or more. Think about the guy behind you, as well as yourself!
The most common gaps I see are the first car in line at a lowered railroad crossing gate. The gate is down, but they come to a stop about 2 car lengths behind the limit line. Are they afraid of a derailment?
Also, I always thought that when you rear-end another car, that always causes your car to fly up into the air, careen over the other car, rotate upside down, and land on the roof. I’ve seen this happen a lot. Just watch CHiPs, T.J. Hooker, and Dukes of Hazzard, and you’ll see.
How would you propose that your average Joe Idiot (myself included) do that “spread of two seconds” calculation (constantly) while driving, if not using some sort of easily remembered car-lengths formula?
This is one of my pet peeves, but only in one particular intersection. There is a left turn lane onto the freeway onramp which is preceded by an additional traffic light. If everyone cooperates by leaving small normal gaps, and drives quickly, you can fit 7 cars in the left hand turn lane between the two traffic lights. If everyone left one car length, you could only fit 4 cars.
If you dillydally, then less than 7 cars can make it through the green light into the left hand turn lane. Anyone who ever drives this intersection and is mildly cognizant will realize this fact. Get your ass in gear and don’t leave large gaps, then you don’t lose the additional 5 minutes it takes for the stoplights to cycle. Cars can be backed up 20 deep, so you may have to wait 4 stoplight cycles.
The most irritating thing to me about those gaps is that those trying to get into a left turn lane cannot access the lane because the idiots going forward are leaving those huge gaps between them; we left-turners are stuck behind them.
As the majority of signals are programmed here, the left turn lanes proceed first, then their lights turn red. The straight ahead lanes’ lights turn green and they proceed through the intersection. The left turners who were stuck behind them can then move into the left lane and wait as the cross traffic shuffles through their lights.
I don’t know how well I’ve described this, but if you’ve stewed through it you know what I mean.
Other than those who don’t bother to signal, the gap people irritate me most.
Is it that hard? When the car in front passes something–either a sign, or a fire hydrant, or a dead dog in the road, or anything–you start counting. If you get to 2 before you pass the same object, back off. If you pass 2 before you pass the object, you can close your gap. Even a Joe Idiot can count to 2.
Good luck trying that in any large city that any doper here, worldwide, posts from. Joe idiot can do it, but Joe Asshole will slot into that space quick as look atcha. May I be the first to admit I DO NOT KEEP A TWO SECOND GAP in the city.
I hear ya, and you’ve explained it perfectly well. The exit from our Costco is that way, and the dual left turn lanes are about a 1/4 mile long. If people would drive forward and equally distribute themselves in both lanes, a lot more people could go on each green arrow.
