When you're driving, how can you tell if the vehicle behind you is too close?

Question

When you're driving, how can you tell if the vehicle behind you is too close?

Answer 1

If you see nothing but grill in your rear view mirror, They're driving too close.

Answer 2

they are too close if you slam on your brakes and they run into you

Answer 3

I'm usually to busy watching my own driving to worry about the car behind me. not much you can do about it anyway.

Answer 4

There should always be a gap of 2 seconds between vehicles. That is, when the back of one car(you) passes a fixed point (a road sign) it should take 2 seconds for the car behind to reach that same point. This is good for any speed.

Answer 5

Are they making you uncomfortable?    If so, they are too close.  

You should be able to see pavement between vehicles in your rearview mirror.    

As you pass an object,  count 4 seconds.  It they reach that object before you count,  they are too close.

Answer 6

If you cant see the other vehicles complete hood from your rear view mirror then they are too close....

Answer 7

If they're so close I cannot even see their headlights, then they are really pushing it. But I think that unless I can see the whole car, tires and everything, they are too close. Especially for freeway speeds.