Caveat: I drive in the UK so driving quality may be different here. I always maintain adequate stopping distances on busy motorways. People do fill those gaps o

Caveat: I drive in the UK so driving quality may be different here. I always maintain adequate stopping distances on busy motorways. People do fill those gaps occasionally and it does result in me driving slightly slower on average by a couple mph maybe, but it's perfectly possible to maintain a gap. A lot of experienced drivers here claim it's impossible too, but there's a good way to know that it's not: on your driving test, you'll fail for following too closely, so most people manage to keep an adequate stopping distance for the test. Following closely is usually a habit picked up when someone becomes a more confident driver. The real reason is probably people don't want to take the tiny average speed hit or find it unfair that they keep letting people in.