Edit since there are multiple similar replies: I took parent comment to include freeways.
Edit since there are multiple similar replies: I took parent comment to include freeways.
> [...] The premise is simple: drivers will make occasional mistakes—veer a bit out of their lane, fail to brake hard enough, etc.—-and if the street is wide, with high visibility in all directions, and free of immediate obstacles such as trees and fences, those mistakes won’t be catastrophic. The problem: this street feels too forgiving to a driver. Too safe and comfortable. So drivers speed up. The engineers didn’t account for this aspect of human psychology.
Drivers behave as expected when they can't see around obstacles, the lane feels tight, and there are curves and other features that reduce visibility. These roads aren't inherently more dangerous, they just give drivers less margin for taking excessive risks.
Most traffic calming measures are similar: break up long sight lines, narrow the lanes, and tighten the corners so people look at the road and think “I’m driving past homes where pedestrians are” rather than “freeway, time to see if I can avoid dropping under the speed limit the whole way!”