Just to add to the bitch-at-porsche...

If you are following someone, you *should* have about 2 full seconds between you. AND when you are pulling up behind someone, you SHOULD be able to see their tires over your hood.

If you don't...you're too close.
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"Nature has constituted utility to man the standard and test of virtue. Men living in different countries, under different circumstances, different habits and regimens, may have different utilities; the same act, therefore, may be useful and consequently virtuous in one country which is injurious and vicious in another differently circumstanced" - Thomas Jefferson, moral relativist