Distance between vehicles at a red light

[TomSeller]

If it is a monster truck in front of me, I always do.

 

[sailorman]

I do .

 

[MNBobcat]

A coworker keeps telling me "You should be able to see the tires of the vehicle in front of you when you are stopped. We got into a heated discussion today... as he stopped a car length back and stated " It's what the insurance people say to do" I looked in my mirror at all of the traffic behind me and thought about how much slower traffic would flow if everybody followed that logic. When at a light I shift into neutral, press down on the brake, and watch what's going on around me.

How many of you follow the "see the tires of the car in front of you" logic? Should I go back to driving school? (In 40+ years I've driven well over a million miles and never hit anyone; but have been rear ended multiple times)

He is right and you are wrong.

The reason for that spacing is this...say you're stopped and you see the car behind you coming at you at 60 mph with no plans to stop. You're about to die. That spacing, of being able to see the tires of the car in front of you, is enough to allow you room to turn out of the way and escape before that car behind you rear-ends you. If you were too tight to the car in front of you, you couldn't duck out of the way.

There have actually been people who saw they were going to get rear-ended and they ducked out of the way and instead the car in front of them got rear-ended.

The spacing is part of a defensive driving strategy.

My dad wrote a driver's training manual for the telephone company probably 35+ years ago and that was one of the things he taught me. So, yes, you should always stop far enough back that you can see the tires of the car in front of you. Now you know why.

 

[TomSeller]

I got rear ended recently with $3500 damage. Not much but it definitely was hard enough to bounce me forward. I had stopped probably further back than is described here and needed all of that space to stop before hitting the car in front of me. I don't understand the comment about traffic flowing slower correlating to the distance between cars stopped at a light.

 

[s219]

I looked in my mirror at all of the traffic behind me and thought about how much slower traffic would flow if everybody followed that logic.

My first year in grad school I had a class in nonlinear wave propagation, which happens to be used to model traffic flow. It significantly influenced my thinking in congested traffic, when merging lanes, etc.

One thing we learned was that traffic flows smoother and will be able to pull away from a red light faster if there is space between cars. I forget the optimum number, but it was about 8-10' or so, which might be enough to see the rear tires or back bumper.

Anyhow, the idea is that when the light turns red, if there is sufficient space between the cars, they can all begin accelerating and moving together. When cars are bunched up, they start moving one at a time, front to back, as if a "wave" rolls back through the lane.

Years later I bumped into a VDOT engineer at a picnic, and we got talking about that, and his eyes lit up. He had no background in the theory, but he knew the practical side of traffic studies and planning, and he said it was exactly true. Worst thing cars can do is bunch up at a light. Any increase in the density of cars in the lane is offset and then some by the fact that the cars begin accelerating one at a time, from a standstill. So if you're the tenth car back, for example, you have to wait for 1 to move, then 2 to react and move, then 3, then 4, etc... until car 9 moves, and then you react and move. That's a bunch of delays. With good spacing between cars, you can all start rolling more or less at the same time, and more cars will make it through the light.

This is pretty easy to test in practice, though getting a whole line of cars to try it is probably impossible. But if you're ever #2 in line at a red light, keep about 8-10' of space, and when the light turns red, you can begin moving at the exact same time/speed/acceleration as car #1.

 

[almaryholm]

Go for it s219...I remember reading about a traffic study done in about the 70's I guess, about spacing and how many more vehicles would get through changing traffic signal if more space was allowed between vehicles so ALL could accelerate at same time, rather than having to wait for vehicle in front of yours to start moving.

 

[Wagtail]

That's how I learnt to drive. Stop whilst you can see the tyres or the bottom of their bumper.

Another reason for that (on top of those mentioned) was due to manual transmissions & the vehicle ahead rocking back before accelerating.

 

[MossRoad]

My folks taught me when pulling up to stopped cars at a light to leave enough room for an escape route without having to back up, and that's what I've taught my kids.... only its not an escape route for wrecks, its and escape route to get away as we live in a very high crime rate area! We look for curbs to jump, poles to drive between, fire hydrants to avoid, etc.... sad, but true.

 

[Garandman]

Sheesh, in Boston they don't leave that much space at 50 mph.

And you know this, how?

Although competition is tight, the worst drivers in Boston are NH commuters. They can't leave an extra half car length because it would add 0.5 seconds to their 80 minute commute. They're nuts.

 

[PhysAssist]

That's what they taught me in drivers Ed 35 years ago. I still try to do that. Gives some stoping space when you are rear ended

Sent from my iPhone using TractorByNet

Me also for the same reason. Also, while I coast to lights amd stop signs in neutral, I was trained to have the car in gear at the light, but for that, I have to admit that I'm not sure why.