The Interstate System is the highest-order functional system. In 2000, it included 46,675 route miles. About 71 percent of these miles were in rural areas, and 29 percent were in urban communities. Between 1993 and 2000, rural Interstate route miles grew by about 0.2 percent annually, while urban Interstate route miles grew by about 0.6 percent annually. The Interstate System included 55,679 bridges in 2000.

Travel on rural and urban Interstates grew faster between 1993 and 2000 than on any other functional system. Congestion has also increased. The percent of congested daily travel grew from 26.7 percent in 1997 to 29.1 percent in 2000. Conditions, however, have mostly improved. The percent of Interstate miles with "Acceptable" ride quality, for example, increased between 1993 and 2000.

An average highway preservation investment of $2.95 billion on rural Interstates would be sufficient to maintain average pavement condition at its current level. For urban Interstates, this number is $5.24 billion.

For rural Interstates, average user costs would be maintained at an average annual investment level of $4.65 billion. For urban Interstates, this number is between $15.7 and $16.3 billion.

Current levels of highway preservation and system expansion investment on rural Interstates are close to the levels that would be necessary to maintain conditions and performance in the future. On urban Interstates, however, substantial increases would be required to prevent both average physical conditions and operational performance from becoming severely degraded.