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.

The National Highway System (NHS) comprises the most important routes for trade and commerce in the U.S. It includes all Interstates and over 84 percent of other principal arterials. The NHS comprises only 4.1 percent of total road mileage in the U.S. but accounts for 44.3 percent of total VMT.

About 48.3 percent of NHS VMT is on pavement with "Good" ride quality, and 90.9 percent is on pavement with "Acceptable" ride quality versus 43.3 percent and 86.6 percent, respectively, for overall highway system. The number of NHS bridges rated deficient has decreased from 25.8 percent in 1996 to 21.5 percent in 2000 and the percentage of deck area of NHS bridges rated deficient has declined from 35.9 percent in 1996 to 30.8 percent in 2000.

Between 1997 and 2000, total daily vehicle miles of travel (DVMT) per lane-mile on the NHS increased by 7.8 percent. The rate of growth was greater in rural areas (8.9 percent) than in urban areas (6.8 percent).

An average annual investment of $47.4 billion would be sufficient to make all cost-beneficial highway improvements and eliminate the deficient bridge backlog on NHS roads. This amount is 55 percent above 2000 capital spending on the NHS.

The NHS share of the Cost to Maintain Highways and Bridges is $37.0 billion (49 percent), which is 21 percent above current funding levels. In 2000, capital spending on the NHS was $30.6 billion, or 47.3 percent of total capital outlay. The suggested NHS share of investment at the Cost to Maintain level would be larger (48.7 percent) than the current share, and would be smaller (44.4 percent) at the Cost to Improve level of expenditure.