Today's New York Times Magazine has a good essay by Walter Kirn on some of the problems with low speed limits.
A few years ago in Montana, my home state, there was no posted speed limit on highways, just a vague rule about driving in a "reasonable and prudent" manner. This haziness forced motorists to think, adjusting their speeds according to the conditions while hoping that lurking state troopers agreed with them. I felt flattered by this invitation to use my judgment and drove more consciously than I ever had. I felt like a grown-up. Then they changed the law, instituting a top limit of 75 m.p.h. Suddenly, I was a rebellious child again. Whether it was day or night, raining or sunny, I treated 75 as a new minimum—as the opening bid in a floating poker game.
Seventy-five, you say? I'll raise you four. No sirens yet? I'll raise you six.
Montana's highway death rate did drop—at first—but now it's back up, to near its highest levels. No one knows why, but when I'm feeling contrary I wonder if it's because, in certain realms, responsibility for your own decisions sharpens the senses, while regulations numb them…
Check out the whole story here.