• Background
• System and Use Characteristics
• Physical Conditions
  • Pavement Condition
  • Lane Width, Alignment, and Access Control
  • Bridge Conditions
• Operational Performance
• Safety
• Finance
• Capital Investment Requirements
  • Rural Interstates
  • Urban Interstates
  • Bridge Preservation
  • Current Spending Versus Investment Requirements

Interstate System

This chapter describes the Dwight D. Eisenhower System of Interstate and Defense Highways, commonly known as the Interstate System. The Interstate System is the backbone of transportation and commerce in the United States. This chapter provides a snapshot of the physical conditions, operational performance, finance, and investment requirements of the Interstate System. This chapter also represents a supplementary analysis to those of the larger, national road network presented in Chapters 2 through 9 of the report.

Background

On June 26, 1956, President Dwight Eisenhower signed the Federal-Aid Highway Act of 1956, one of his top domestic priorities. President Eisenhower wrote in his memoirs that "more than any single action by the government since the end of the war, this one would change the face of America. Its impact on the American economy—the jobs it would produce in manufacturing and construction, the rural areas it would open up—was beyond calculation."

The 1956 legislation declared that the completion of a "National System of Defense and Interstate Highways" was essential to the national interest. This system was designed to facilitate military transportation during the Cold War, but it had countless other economic and social impacts. The Interstate System, for example, accelerated interstate and regional commerce, increased personal mobility, and led to metropolitan development throughout the United States.

The Federal-Aid Highway Act of 1956 called for new design standards, began an accelerated construction program, and established a new method for apportioning funds among the States. At the same time, the Highway Revenue Act of 1956 introduced a dedicated source for Federal highway expenditures. It created a Federal Highway Trust Fund financed by highway users, allowing massive investment in infrastructure projects. Between 1954 and 2001, the Federal government invested over $387 billion on Interstates through apportionments to the States.

The National Highway System Designation Act of 1995 included the Interstate System as the core of a National Highway System (NHS), described in Chapter 17.

System and Use Characteristics

Exhibit 16-1 describes the total public road length of the Interstate System (data for all roads can be found in Exhibit 2-6). The route miles of the Interstate System in the United States increased from 46,675 in 2000 to 46,747 in 2002. About 70.8 percent (33,107 route miles) were in rural areas, 3.9 percent (1,808 route miles) were in small urban areas, and 25.3 percent (11,832 route miles) were in urbanized areas. By comparison, of the total 3,981,670 route miles for all roads in the United States, 77.4 percent (3,079,757 route miles) were in rural areas, 4.6 percent (183,503 route miles) were in small urban areas, and 18 percent (718,410 route miles) were in urbanized areas.

The number of Interstate route miles in rural areas declined from 33,152 in 2000 to 33,107 in 2002. During the same period, the number of Interstate System miles in small urban areas increased from 1,794 in 2000 to 1,808 in 2002 and in urbanized areas the number of route miles increased from 11,729 in 2000 to 11,832 in 2002. The decrease in rural route miles is the result of changes in urban boundaries based on the 2000 decennial Census, which caused some formerly rural areas to be reclassified as urban. Note that some States are typically faster than others in modifying their data reporting to correspond to new decennial Census information; consequently, the next edition of the C&P report may show additional rural Interstate mileage having been reclassified as urban.

Between 1993 and 2002, rural Interstate route miles increased by about 0.1 percent annually, small urban Interstate route miles increased at an average annual rate of 0.7 percent, and Interstate route miles in urbanized areas increased 0.5 percent annually. The 0.2 percent overall annual growth rate for Interstates roughly matches that for all roads during that time period.

Exhibit 16-1 also describes the number of Interstate lane miles between 1993 and 2002 (lane mileage data for all functional systems can be found in Exhibit 2-7). In 2002, there were 210,896 lane miles of Interstates in the United States. About 64.0 percent (135,032 lane miles) were in rural communities, 3.6 percent (7,776 lane miles) were in small urban areas, while 32.3 percent (68,088 lane miles) were in urbanized areas. By comparison, about 75.7 percent of all highway lane miles in the United States were in rural areas, 4.7 percent were small urban areas, and 19.6 percent of lane miles were in urbanized areas.

Between 1993 and 2002, rural Interstate lane miles grew by 0.2 percent annually, small urban Interstate lane miles grew at 1.0 percent annually, and urbanized Interstate lane miles grew by 0.9 percent annually. The annual growth rate of lane miles from 1993 to 2002 for the total Interstate System was 0.5 percent annually or almost double the annual growth rate of lane miles for all roads in the United States over the same period. This growth in Interstate lane miles has occurred due to both new construction and the reclassification of some arterials to Interstate status.

Exhibit 16-2 describes the number of Interstate bridges in 1996, 1998, 2000, and 2002. (Data for all bridges can be found in Exhibit 2-15.) Between 1996 and 2002, the number of rural Interstate bridges dropped from 28,638 to 27,316 bridges, while during the same period, the number of urban Interstate bridges increased from 26,596 to 27,929. The reduction in rural bridges is caused in part by the reclassification of some rural Interstates to urban status as communities have grown in size.

Exhibit 16-3 describes vehicle miles traveled (VMT) on Interstate highways between 1993 and 2002. Use data for all roads can be found in Exhibits 2-8, 2-9, and 2-10. In 2002, Americans traveled approximately 282 billion vehicle miles on rural Interstates, 22.6 billion vehicle miles on small urban Interstates, and in excess of 389 billion vehicle miles on urban Interstates. Interstate travel continued to represent the fastest growing portion of VMT between 1993 and 2002. Interstate VMT grew at an average annual rate of approximately 3.1 percent between 1993 and 2002, while VMT on all roads grew by about 2.5 percent annually.

Exhibit 16-4 describes Interstate highway travel by vehicle type between 1993 and 2002. In 2002, 80.5 percent of travel on rural Interstates was by passenger vehicle; 3.1 percent was by single-unit truck; and 16.4 percent was by combination truck. About 91.9 percent of urban Interstate travel was by passenger vehicle; 2.2 percent was by single-unit truck; and 5.9 percent was by combination truck. By contrast, passenger vehicle travel represented 92.5 percent of travel on all roads in 2002. Single-unit truck travel represented 2.6 percent of travel, and combination truck travel represented 4.9 percent.

Travel on rural and urban Interstates grew faster than on any other functional system. Between 1993 and 2002, for example, combination truck travel grew by 4.4 percent annually on urban Interstates and by 3.7 percent on rural Interstates. By comparison, combination truck travel on all roads increased by 3.3 percent annually between 1993 and 2002.