While the road I live is a county highway, it's not exactly the most heavily traveled road in the area, let alone the world. But it's become even less populated over the past two weeks, as the county has closed it down to fix a deadly curve and do some other work not far from my house. There are barricades and a sign down where my half connects to another county road warning that the road is closed.
Still, plenty of people come down, hoping to cut about ten minutes off the drive to town (it is convenient for that, when open).
I figure one of two things is going on. Either (a) they can't read, or (b) they distrust the government so much that they don't believe the signs.
Addendum: Having conducted an informal survey of the last six vehicles and discovered that two were Mercedes, one a BMW, and another a highly-pimped-out four-door pickup, I'd say the reason is definitely (a).