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Comment by lutorm | Hacker News Reader

* ... should typically be able stop a car length per 10mph.*

This is not correct, stopping distance scales as the square of speed. The distance you'd need to stay from the vehicle in front to be able to stop if it magically came to an instantaneous stop is far, far larger than anyone will reasonably keep.

The stopping distance at 65mph, including reaction time, is at least 300ft. That's ~20 car lengths, not 6.5 that your formula would yield. If conditions are wet, your tires are not in great shape, or you're not paying attention, it's going to be much longer.

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Cars in front don't usually hit walls while they're traveling. It takes a while for the car in front to stop too.

The scenario under discussion is when the car in front doesn’t stop but changes lanes, revealing a stopped car in your lane right where a moving car had been. It’s like the car in front of you was suddenly stopped by magic.

The solution is typically to swerve with the other car, but sometimes that’s not possible.

But it is possible, when the cosequence is someone dying, the likelihood do not need to be high to act carefully. Anyway the example here was about a car in front avoiding a stopped car.

The thread is about how closely to follow a car. If the car is stopped, the answer is "as closely as you like, it's not moving".

This thread is about how closely to follow a moving car. The worry is if the moving car suddenly switches to being stopped. Will you be able to also switch to being stopped before hitting it?

Yea, some people seem to miss that just because the car in front of you can jump over in another lane doesn't mean you can at all. If you have a car beside you, and the car you're tailgating does not, then you're screwed in an emergency situation like this.

I'm convinced that if police ticketed people for tailgating like they do for speeding it would save thousands of lives.

Correct. Now please tell the goddamn drivers in the Seattle area. They aren’t listening to me.

Drag works the same way, which is why a pickup truck can stop from 90 mph relatively quickly

Drag is insignificant compared to brakes, unless you're going very very fast.

if that were the case, cars would just casually accelerate up to near Mach 1 without any issue.

No, because the engine is also insignificant compared to the brakes. A SUV might have brakes (briefly) capable of 900 HP of power absorption

If a car has its brakes on, it'll be extremely hard to accelerate. The brakes create more movement resistance than air resistance does.

If a car has its brakes on, it'll be extremely hard to accelerate

It should be impossible to accelerate. None but maybe the most high-output engines should have enough power to overcome the car’s brakes. Aerodynamic drag is not quite a rounding error, but I don’t imagine it counts for a whole lot in this scenario in comparison.

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