Transportation Infrastructure and Management of Existing Traffic Flow
In addition to its reliance on oil, the transportation sector also relies heavily on the existing infrastructure of roads and highways. Under the Intermodal Surface Transportation Efficiency Act of 1991, the Federal government plays an important role as overseer of the National Highway System to ensure that the highway system is "economically efficient and environmentally sound, provides the foundation for the Nation to compete in the global economy, and will move people and goods in an energy-efficient manner." In recent years, however, the road and highway infrastructure has not kept pace with the number of miles driven in the United States. When more people use a roadway than the capacity for which it is built, traffic slows. Commercial trucking—the most common method of moving freight across the United States—is increasingly reliant on urban interstate highways, many of which are congested. Between 1982 and 2003 the share of roads in U.S. urban areas that are congested rose from 34 percent to 59 percent. Changes in commuting patterns have also spread congestion to more roads. The traditional suburb-to-city commute has diminished in importance: As of 2000, half of all commuters drove to jobs in the suburbs, while only 20 percent drove to jobs in central cities.
Congestion is defined as the marked slowing of traffic as a roadway reaches capacity. Congestion in the United States manifests itself primarily as a bottleneck on a roadway. A bottleneck is a hindrance to vehicle movement because it involves delays at key intersections, backed-up traffic, or narrow or obstructed sections of a roadway. Unexpected events such as accidents or other traffic incidents also cause congestion on crowded roadways. Together, they are responsible for 65 percent of all congestion.
It is important to note that roadways are not congested at all hours of the day. For instance, on one particular roadway in the Seattle area, a trip that occurs prior to 6 a.m. or after 10 p.m. takes about 10 minutes. That same trip takes about 30 percent longer at 8 a.m. and almost twice as long at 6 p.m. due to slowing traffic. This general trend appears in many U.S. cities and suggests that it is the timing of vehicle miles traveled more than their growth that is at the root of the congestion problem.
One underlying reason why congestion exists on U.S. roadways is the lack of a private market to price roadway use. Most roads in the United States are provided by the government, are open to all, and are free of charge. Economists generally believe that a good may be better provided by the government when it is difficult for private markets to charge for its use. Because one motorist's use of a congested road reduces the road's value for other drivers and drivers can be selectively prevented from entering the roadway through the use of gates or technologies that monitor use, it is increasingly appropriate to charge drivers for some roadway use in the same way the private market charges for other goods and services.
A driver decides which road to use based on private needs: for instance, the shortest distance or fastest route between destinations, or the closest, most accessible highway. The fact that each driver decides on a route independently of other drivers is not a problem when the number of drivers is well below the roadway's capacity. However, when drivers have free access to roads, crowding occurs at times of high demand, decreasing vehicle speed and flow. Each additional driver slows down other drivers on the roadway, causing them to lose time and to burn extra gasoline. However, drivers typically do not consider the added costs they impose on others. This is a "get in line" or "queuing" approach to allocating road space. When there is a shortage of something— for instance, space on a ski lift, or attendants at the Department of Motor Vehicles—those willing to get in line and wait eventually receive what they want. This approach to road-use management is inefficient because it allocates road space to those with the time to wait in traffic, not necessarily to those who value its use most highly.
If a roadway is priced—that is, if drivers have to pay a fee to access a particular road—then congestion can be avoided by adjusting the price up or down at different times of day to reflect changes in demand for its use. Road space is allocated to drivers who most highly value a reliable and unimpaired commute. This arrangement encourages drivers to consider the tradeoff between the price of using the road and the additional time and inconvenience of using a nonpriced, alternate route, or driving at a noncongested time. Drivers who place a high value on the predictability and reduced time of commuting, for instance, a doctor who has been called to the hospital for an emergency, have the option to pay for access to noncongested roads. Drivers with more time flexibility, for instance a person doing his or her grocery shopping, can avoid the road and the fee. They can use alternative but more congested roads, shift when they drive to nonpeak hours, or use mass transit when it provides a cheaper alternative to driving. The average cost to each driver falls because drivers have a choice in how they pay for roadway use, in time or in money.