Las Vegas is the only place I've ever driven where people routinely drive under posted speed limits. This probably isn't the result of an excess of caution or a desire to save fuel by going slower - on the highways, people dart all over the road as speedily (and as blindly) as maniacal bats out of hell. But on main thoroughfare streets, nearly all of which have six roomy lanes as well as wide, convenient and separate left- and right-turn lanes just about anywhere you might think of wanting to turn, drivers tool along between 30 and 35 mph even though the speed limit is 45. Often, there is one such stately driver in each of the three lanes going your direction. It's like being behind the front phalanx in some sort of boring parade. You're just stuck.
I've been trying to figure out why anyone, faced with a stretch of open road, wouldn't promptly accelerate to the speed limit. (I don't wonder why the slowpokes can't just get themselves the hell into the right lane where they belong. It's plain when you look into their windows as you pass them that they are simply oblivious, sometimes because they're gabbing animatedly on cell phones, sometimes because they just have that look of a person who might as well be living alone in the world for all the consideration he/she shows for everyone else.)
I think the explanation may have something to do with how people react to wide open spaces depending on whether they've always had them or never had them. Those of us who spent most of our driving time on narrow, crowded Eastern or Midwestern streets where the traffic usually moves like molasses if it moves at all, can't help feeling a surge of joy, followed instantly by a surge of acceleration, whenever we see in front of us a stretch of open road. Is there anything more wonderful to a Chicago commuter, for example, than a sudden multi-car-length open space after an hour of crawling along on the Kennedy behind the same bumper? I don't think so.
(It used to take me hours to get bumper sticker slogans out of my head. Why is it so hard to stop reading those things over and over and over when they're emblazoned on something peeling off a bumper a few inches in front of your car? During my commuting years, I developed a whole theory about the mean-spirited "mine is better than yours" theme that characterizes so many bumper stickers, but that's a post for another day.)
Unlike drivers accustomed to very little in the way of opportunities to go 45 mph on city streets, people who learned to drive in the wide open west (or have assimilated it better, evidently, than I have) respond totally differently to the chance to go fast. They seem to feel no need whatsoever to take advantage of it.