While this report does not recommend any specific level of investment, a comparison of the investment requirement scenarios with current and projected spending levels provides some insights into the likelihood that the level of performance implied by the scenarios will be attained.

Federal, State, and local highway and bridge capital outlay expenditures totaled $48.7 billion in 1997. Capital outlay expenditures by all levels of government would need to increase by 16.3 percent above this 1997 value to reach the $56.6 billion Cost to Maintain Highways and Bridges level. Similarly, an increase of 92.9 percent would be required to reach the $94.0 billion Cost to Improve Highways and Bridges level.

Capital improvements to existing bridges totaled $6.1 billion in 1997, above the $5.8 billion level of the bridge Maintain Backlog scenario (included in the Cost to Maintain).

Recent editions of the C&P report have shown that capital spending has been growing more quickly than the investment requirements. This trend is expected to continue in the near future, as the implementation of the TEA-21 will result in significant increases in Federal highway funding. Assuming the continuation of recent trends in State and local government funding patterns, capital spending should reach the Cost to Maintain level by 2003.

While the Cost to Maintain is 16.3 percent higher than 1997 capital spending, this difference is expected to shrink to 5.7 percent over the full 1998-2003 period.

In 1997, 47.6 percent of highway capital outlay went for highway and bridge preservation. If future funding remains near current levels, the analytical models used to develop the investment requirement scenarios in this report suggest that a greater share of capital investment should be devoted to system preservation. For the Cost to Maintain, 56.1 percent of the projected investment requirements are for system preservation. If funding increases significantly, the models recommend increasing system expansion investment more quickly, so only 51.2 percent of the Cost to Improve is for system preservation.