it's how fast you can stop.
I remember my first fast car. Well, my only fast car. A '72 Cougar I acquired in 1985. It handled like a charm. Zinging around corners. If I drove 85 on the highway it got 29 mph. (around town was only 8 mph, but I looked good in it.)
SUV's, big cars, big trucks, these are vehicles designed to go fast. But they don't stop fast.
"Braking distances" advertised by manufacturers don't factor in the amount of time it takes your brain to think about what's coming up, instruct your foot to move to the brake and push it, and start pushing it. On dry roads, "thinking distance" adds about 25% more time to stopping. So if braking distance in circumstance A is 100 feet, and you're actually looking right at the car ahead of you when it slams on it's brakes, so you see right away that you need to stop too, you've got to be 125 feet back from it to stop in time. Of course, if you're on your cell, or flicking ashes, or combing your hair, or swatting at your kid in the backseat the thinking time goes up exponentially until you notice there's a problem.
On wet roads, the stopping distance is just less than double what it is on dry roads.
So Why, oh Why, do big vehicles drive 65-80 mph 1 car length off the rear end of the car in front of them?
You have to have the thinking time distance, at a minimum, in order to stop without rear ending the car in front of you.
I say you, and I could also mean me.
But I don't.
Safe following distances used to be the 2 second-rule, or the 3 car length rule. Now it's this:
Dry, clear road you need a two- or three second gap.
If you are on a wet road then you need to have at least a four-second gap.
And if it's icy or you are driving on compacted snow or somewhere you know that something slippery (such as diesel fuel) has been spilled, then it is wise to create at least a ten-second gap.
Three car lengths is the closest I'll get on the highway, and people are constantly cutting in front of me around town because I leave more than one car length between me and the car in front and so, I guess, what, people think I was just saving them a place?
I'm pretty big into getting there in one piece, ("it's better to test your patience than to test the resilience of your head as your car slams into the vehicle ahead") even if it means I get there a couple of minutes late. And I learn to leave earlier next time.
Are you a big car driver who cuts me off and tailgates? Can you explain to me the rationale?
Really, I'm sure it must make sense to you, so please, hit comment and let me know.