Air Travel is frequently the most practical method of covering the large distances between sights in the USA. It is the fastest, the most
convenient and frequently the most economical means of transportation. You can usually purchase an airline ticket from New York to Los Angeles (a distance of 3000 miles or 5000km) for under $400 and sometimes under $300 by taking advantage of special promotions. The trip via airplane takes only 5 hours. Train fare between the same cities costs about $300 to $500 (with limited sleeping accommodations and requires a minimum of 3 to 4 days. The transcontinental bus costs about $225 and requires at least 3 days of incessant travel. You could drive it in about 5 days, but the gasoline and lodging alone will likely cost considerably more than the airfare.
Trains are not a good choice in the US
Trains are not as popular in the USA as they are in many other countries. They are an acceptable choice only for short or medium distance travel in certain areas. In many major cities, commuter trains provide good passenger service from suburban communities to the downtown metropolitan centers. The East Coast corridor from Boston to Washington DC through New York City and Philadelphia is well serviced by the high speed Metroliner. In other parts of the US, train service may be infrequent or even non-existent.
Busses are an economical option
Bus transportation is a great option for urban or suburban transit, but bus service can be very limited in rural areas. The Greyhound Bus line offers inter-city and transcontinental bus service. It can be an inexpensive alternative to other forms of travel if you are willing to put up with the discomfort of long rides with minimum comforts.
Cars are almost a necessity
In many parts of the USA where public transportation is inadequate or non-existent, a car is a practical necessity. In most large cities, the major shopping centers and sports or entertainment facilities are usually located in the suburban communities far from the metropolitan center. Without a vehicle, sightseeing, shopping and touring can be very inconvenient.
Hitchhiking is not permitted in most states
Hitchhiking is illegal in many states. You may occasionally see a person trying to "hitch a ride" along an interstate or at the entry to a toll road, but they are often risking a fine if apprehended by a police patrol.
Bicycles are a good way to see the USA
If you have enough time, you can bicycle across parts of the USA and enjoy the scenery. Just remember that bicycles are not as common in the US as they are in many other countries, so car and truck drivers are not as accustomed to bicyclist on the roads. Be cautious! Bicycles are banned from the freeways and interstate highways, but are permitted on all other roads. Many cities and towns have off-road bicycle paths and trails.