The economies of many cities and urban areas depend on the efficiency of transportation, both for workers and goods. Therefore, most urban areas have some sort of public transportation system available. While these systems are put into place to ease congestion and promote transport, there are still problems that occur and need to be overcome.
Public transportation systems, such as buses, subways and commuter rails, can be either underused or overused. During peak hours, there are not enough transportation vehicles available, which results in overcrowded vehicles and discomfort for passengers. These peak hours are normally from 7 to 9 a.m. and from 4 to 6 p.m., when employees are travelling to and from work. At times other than peak hours, such as the middle of the day and evenings, the vehicles are underused. Underused transportation, or empty subway cars and buses, means the system is financially unsustainable. Assigning more buses or subway cars to peak hours and reducing the number of these vehicles during off hours is one way to overcome this problem. However, knowing just how many vehicles are needed for each time requires some trial and error.
Most public transportation systems service only areas that have high population density. These services do not expand outside of the large urban areas. This is mainly due to the fact that decentralisation is expensive, and longer trips result in high operating costs and lower revenue. Some of these costs may soon be able to be offset by using renewable energy sources and alternative fuels, but decentralisation is still an issue that needs to be investigated for public transportation systems.
Most public transportation systems have developed a flat fare payment structure. In many cases, this flat fare actually discourages shorter trips by making longer trips less expensive. This is ironic, since most public transportation systems are designed for shorter rather than longer trips. Public transportation systems that use fare systems based on the distance travelled are more desirable to commuters and are financially sustainable to the public transportation system.
Some public transportation systems are fixed, as trains and subways must travel over specific tracks. In a fixed system, the route the vehicle travels cannot be changed, but is permanent. A bus route is not fixed, because the driver can change the route by taking different streets; however, a subway route is fixed, as the subway can only travel through the specified subway tunnels. This causes difficulty when the city changes or routes need to change. Changing subway routes and adding new lines is costly and time-consuming. For most fixed systems, the cities travel patterns will change, but the public transportation system will not change.