if you are meaning the US, well, it's obvioulsy the car. however, the depression was ravaging the US economy, so it was hard to get one let alone enough to eat.
Because you don't need gas for it.
cars if the road is short and planes if you are going long distances
the train was the most popular way to travel, if you could afford it. Trains were a way of travel for the middle and upper class citizens.
Stagecoach
bridges are use for transportation and building.
The most popular way of communication is the mobile phone
Spanish modes of transportation, in order of popularity, are automobile, train, and bus.
The best way to save energy in transportation is to increase the fuel efficiency of motor vehicles.
The most popular way is with a soup. Either vegetable soup or chicken soup.
Railroads, I believe.
A popular way of a prisoners execution is usually by an electric chair
The most popular methods of transportation for getting from Halifax to Boston are flying, taking the Greyhound, driving, and/or taking a train.