5 Road transportation
5.1 Infrastructure and private automobile use
5.2 Intercity bus
5.3 Congestion
5.4 Cargo
5.5 Roadway links with adjacent countries and non-contiguous parts of the United States
6 Air transportation
7 Rail
7.1 Passenger
7.2 Cargo
7.3 Railway links with adjacent countries
8 Mass transit
8.1 Legislation
9 Water transportation
9.1 Waterways
9.2 Ports and harbors
9.3 Merchant marine