National Highway System
The National Highway System (NHS) has five components, including (1) the Interstate System, (2) selected other principal arterials deemed most important for commerce and trade, (3) the Strategic Highway Network (STRAHNET), (4) STRAHNET connectors, and (5) intermodal connectors that provide access between major intermodal passenger and freight facilities and other NHS components. The NHS includes 87.5 percent of urban other freeways and expressways, 35.9 percent of urban other principal arterials, and 83.8 percent of rural other principal arterials. While the NHS makes up only 4.1 percent of total U.S. mileage, it carries 44.8 percent of total travel.
In 2004, 68.0 percent of rural NHS travel was on pavements with good ride quality, compared with 42.5 percent of urban NHS travel. Approximately 97 percent of rural NHS travel was on pavements with acceptable ride quality, compared with 86.9 percent of urban NHS travel.
In 2004, 19.4 percent of all U.S. bridges were located on the NHS, but these bridges had 49.5 percent of the total deck area on all bridges and carried 71.1 percent of the traffic on all bridges. Approximately 20.5 percent of NHS bridges were considered deficient in 2004, including 5.6 percent classified as structurally deficient and 14.9 percent classified as functionally obsolete.
In 2004, all levels of government spent a combined $34.6 billion for capital improvements to the NHS, which was 49.2 percent of total capital expenditures on all roads. If current spending for NHS bridge rehabilitation and replacement were sustained in constant dollar terms over 20 years, the current backlog of deficient bridges could be reduced, but not eliminated. If current spending levels on the urban NHS for system expansion plus pavement resurfacing and reconstruction were sustained, urban pavement condition and operational performance would be expected to decline. Current spending on the rural NHS is adequate to improve rural conditions and performance.