In America, the car is king, and due to the size and sprawl of the major cities in the country, it is always a good idea to rent a car for the duration of your stay. Public transport is an option for some journeys, and taxis tend to be a sensible option late in the evening after a night out. If you want to explore the countryside surrounding the city in which you are staying, you will find that roads are of a high standard, and getting around on them is simple.
On American roads, you should observe the posted speed limit, and remember that you can make a right turn through traffic lights even when they show red, as long as the road is clear.