In order to have easy mobility of persons and goods, it is necessary to have a sophisticated and widespread transportation system. This system is made up of five primary areas of transportation, which are: - Motor vehicles - Railroad transportation - Air transportation - Water transportation - Pipelines
Each of these five modes consists of different subsystems which make up the system. Each mode is used to transport persons or goods, but in many instances, one mode may be favored over the others. All five modes require some primary source of funds for building and maintaining the infrastructure. These funds may come from a number of different places such as the federal government, state, or the city through which the system runs. Different government agencies have jurisdiction over the modes. These agencies focus on maintaining and improving safety of each system. The individual states also have certain obligations to the operation and regulation of the different modes of transportation.
Each mode is made up of primary subsystems. The subsystems of railroad transportation include freight trains and passenger trains. Freight trains are used to transport goods and materials between cities while passenger trains are used to transport people. Although freight trains are still used all across the nation, rail intercity freight has accounted for a decreasing share of the total ton mileage over the past 30 years. This is mostly due to the increase in truck transport. Rail passenger traffic had also declined over the years until better service was offered by Amtrak and the price of fuel increased. Much of the decline in rail passenger traffic has been due to the increasing number of air passengers. Air transport can also be divided into the subsystems of passenger and freight transport. Passenger air travel has rapidly increased over the years due to: