The U.S. road network: Interstates, State Highways...
In the United States, the road network is very comfortable, well maintained, spacious and airy. In general, locals are solid, respectful drivers, even if they slightly push the limits at times.
In case of problems, the road assistance and emergency services respond almost immediately. You must dial 911 (from anywhere in the territory of the United States).
The road network of the United States is divided into three main categories:
Interstate Highways, the most important link between States.
U.S. Routes or U.S. Highways are the ancestors of Interstate Highways (Route 66 was part of the network). Dating back to the 20s, they generally fail to offer the same comfort as modern highways but more than make up for it with superior scenery and endless side-trips.
Reminder: Each state enacts its own traffic rules. Speed limits may change as the laws on wearing seatbelts, talking on the phone while driving, drinking and driving, etc.
Funded by the federal government, Interstates connect U.S. states. Each state can determine the speed limit on Interstates crossing its territory, usually between 70 and 80 mph. Exits are numbered.
Interstate Highways are indicated on blue panels that display their number, topped with a thin red stripe marked "Interstate". These panels are shield-shaped.
Toll Interstate Highways are usually found in densely populated areas of the country (toll roads are also called "Turnpikes").
U.S. routes or U.S. highways
U.S. highways, Route 66 being a major icon and the most recognizable among them, are the ancestors of Interstate highways. This gigantic network was established in 1926. From the 50s, with the construction of Interstate highways, it has lost part of its relevance.
U.S. Routes are numbered and usually toll-free Odd roads run north-south while even ones run east-west. Their number grows from south to north and from west to east.
They are indicated by white panels with the U.S. wording over the route number. Less comfortable and maintained, and providing a slightly bumpier ride than Interstates, U.S. Routes symbolize the American road trip to meet people, visit forgotten small towns and other ghost towns.
Funded by the states, state highways are a mixture of primary and secondary roads with signage and numbering differing across states. Maintenance also varies greatly.