The maximum speed limit in most states is 65mph (105km/h) although this can vary, so always pay attention to road signs. Where you see two signs displaying speed limits, the higher number will be the top speed and lower number the minimum speed you should travel at.
EVERY STATE HAS DRIVING LAWS THAT ARE DIFFERENT:
It is important to be aware that all states in America has their very own set of traffic rules. It's fair to say that the majority pf the traffic regulations don't vary too much from state to state, but some states have minor differences.
The largest cities in the United States offer carpool lanes on their ring of peripheral highways. During peak hours - usually in the morning and in the evening as businesses open and close - carpool lanes are exclusively reserved for cars carrying two or more passengers. Carpools usually take up the leftmost lane - just one as a rule. Signs also indicate the carpool time limits. Although some locals use carpool lanes as regular passing lanes, I'd strongly advise against it - you're seriously risking a ticket.
GASING UP IN THE USA:
Most gasoline stations require you to pay before filling up -- even if no sign is displayed. In many areas it is payable by credit card. Be aware, however, that some gas stations can and will put a temporary hold up tp $200 on your credit balance if you swipe at the pump; additionally, many pumps now ask for an American zip code. Paying inside can alleviate this problem in some cases, but the best thing to do is simply pay in cash whenever possible.