It's been a while since I drove there, but some points I remember, so think will probably still hold. It does vary a lot from state to state though:
Every - YES EVERY - Police patrol vehicle has a speed device on the dashboard - and if you are going above the speed limit - you WILL get stopped and fined on the spot. The fines vary from state to state, but are often based on the speed above the speed limit. For example, 1 mph above speed limit = $3, 2 mph = $4, 3 mph = $5, 10 mph = $20, 20 mph = $100. Other states are just a flat rate. And yes, they can, and do stop you for 1 mph over the speed limit to collect their $3. Many people there simply see it as a driving tax, and, because there's no points system, no-one's really that bothered, and don't usually argue, although you do have the right to go to court to contest it. Very many people have road angels or equivalents, even though I think they are banned in some states.
Most roads are reasonably well signposted with speed limits (None of this street lamp nonsense), but a 55 mph limit is usually the maximum on single carriageway out of town (Where town = 1 house in the middle of nowhere and out of means at least 5 miles away

).
Another strange thing I found. Here, the green man means you can walk across at lights relatively safely ("Ped Xings" in USA). There the illuminated "Walk" means that traffic going straight on is stopped, but traffic turning left and right can still go over the crossing - they just have to give way to pedestrians. So, if you are turning (Right on red, or left or right on green), beware of Pedestrians crossing. If you are walking, and the sign to cross the road says "Walk", take care of cars, because they don't always give way as they should. Some, incredibly, even drive round you (in front or behind) at high speed while you are still crossing. Very scary.
Finally, school buses. One law that almost all drivers obey. I think the punishment is incredibly severe - possibly even leading to a loss of driving licence (which to an American is almost equivalent to imprisonment). NEVER, EVER overtake a stopped one. If it's a yellow school bus and it's dropping children off or picking them up, you just have to wait. If it's not dropping children off or picking them up - you still have to wait! Only if it's parked, empty, and has no driver can you proceed with caution. This is rare. Best advice - wait. Then overtake recklessly on a blind bend at 110 mph so you don't get caught behind it again. At least that's what many seem to do.
The lanes there are very wide, and there are often several of them so that's quite nice, and out of the major cities the traffic density is much lower, but....
The driving standard is generally much lower
The law allows overtaking on either side
Drivers change lane at will with no rhyme or reason
Drivers drive much longer distances and often drive very tired
Drunk driver punishments are similar, but apparently are not as well enforced, so there are (relatively a lot of drunk (and drugged) driver's on the roads, especially at night.
