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Status of the Nation's Highways, Bridges, and Transit:
2004 Conditions and Performance
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Chapter 16 (Continued)

Capital Investment Requirements

Exhibits 7-2 and 7-3 in Chapter 7 show the estimated average annual Maximum Economic Investment (Cost to Improve Highways and Bridges) and Cost to Maintain Highways and Bridges for 2003-2022, categorized by functional class and improvement type. For the Maximum Economic Investment scenario, investment requirements for rural and urban Interstates total $6.4 billion (5.4 percent of total) and $24.9 billion (20.9 percent of the total), respectively. At this level of investment, all cost-beneficial improvements would be implemented. See Chapter 7 and Appendix A for more on the investment requirements methodology used in this report.

For the Cost to Maintain scenario, the portion of estimated investment requirements on Interstates totals $5.0 billion for rural and $13.8 billion for urban. These amounts are 6.7 and 18.7 percent, respectively, of the total Cost to Maintain Highways and Bridges. At this level of investment, average user costs on all highways in 2022 would be maintained at their 2002 levels. User costs would increase on some sections and functional classes and would decrease on others. In the case of Interstate highways, average user costs in both urban and rural areas would decrease slightly.

Exhibits 16-15 through 16-18 show the impacts of different levels of future capital spending on the physical conditions and operational performance of rural and urban Interstates. The first line in each exhibit shows current values for each of the measures, and the second line corresponds to the maximum economically efficient level of investment. All investment levels are in constant 2002 dollars.

Exhibits 16-15 and 16-17 show the impact of different levels of combined highway preservation and expansion spending on pavement condition, and Exhibits 16-16 and 16-18 show the impact of these same outlays on measures of operational performance. Highway preservation and system expansion investment requirements are modeled by the Highway Economic Requirements System (HERS) (see Appendix A).

Expenditures on system enhancements (including traffic operational improvements, safety improvements and environmental enhancements) are not directly modeled and are not included in the totals shown in the exhibits. Bridge preservation investment requirements are discussed separately below.

Rural Interstates

Exhibit 16-15 shows projected values for average International Roughness Index (IRI), a measure of average pavement condition, and the percentage of VMT at an IRI below 95 and below 170. These two levels are used to define "Good" and "Acceptable" levels of pavement ride quality. (Chapter 3 provides more information on how pavement condition is defined.) The exhibit shows that the 2002 preservation and expansion investment level of $4.99 billion on rural highways is only slightly below the maximum economic investment level of $5.12 billion estimated by HERS.

Exhibit 16-15, projected rural interstate pavement condition in 2022 for different possible funding levels. Line chart with data table. The line chart shows a downward trend for change in average IRI beginning with a ?2.5% change in funding at $3.66 billion to a ?12.3% change at $5.12 billion average annual investment.
Average Annual Highway Preservation + Expansion Investment (Rural Interstates) Percent Change in Average Percent of VMT on Roads withFunding Level Description: Investment Required to...
(Billions of 2002 Dollars)IRIIRI<95IRI<170 
$4.99 73.5%97.3%2002 Values
$5.12-12.3%86.5%100.0% 
$4.94-12.3%85.9%99.9% 
$4.79-12.3%85.4%99.9% 
$4.65-11.1%84.4%99.9% 
$4.45-9.9%82.4%99.8% 
$4.21-8.6%79.9%99.7% 
$4.10-7.4%78.3%99.5% 
$3.96-6.2%76.3%99.4% 
$3.85-4.0%74.6%99.3%...Maintain VMT with IRI<95
$3.66-2.5%71.5%99.1%...Maintain Average IRI
Source: Highway Economic Requirements System.

If current funding levels were sustained, and the mix of highway preservation and widening investments recommended by HERS were implemented, then average IRI would be projected to decline by 12.3 percent over 20 years, and the percentage of travel on roads with good pavement quality would rise to 86 percent. Virtually all travel on rural Interstates would occur on roads with at least acceptable ride quality. The annual level of funding required to maintain Average IRI is below $3.66 billion.

Exhibit 16-16 shows how future values for average delay per VMT (discussed in Chapter 9), total user costs, and travel time costs on rural Interstates would be affected by different levels of highway preservation and expansion investment. Average user costs on rural Interstates would be maintained at an average annual investment level of $3.66 billion, while average travel time costs would decrease at that funding level. Average delay on rural Interstates would be maintained at an investment level between $3.96 and $4.10 billion, and would decline by over 20 percent at 2002 preservation and expansion expenditure levels.

Exhibit 16-16, projected rural interstate conditions and performance in 2022 for different possible funding levels. Line chart with data table. The line chart shows a downward trend for change in average delay beginning with a 14.3% change in funding at $3.66 billion to a -21.9% change at $5.12 billion average annual investment.
Average Annual Highway
Preservation + Expansion
Investment (Rural Interstates)
(Billions of 2002 Dollars)
Percent Change in Funding Level Description:
Investment Required to...
Average Total DelayTotal User CostsTravel Time Costs
$4.99 2002 Values
$5.12-21.9%-0.9%-2.9% 
$4.94-20.3%-0.9%-2.6% 
$4.79-17.7%-0.8%-2.6% 
$4.65-15.9%-0.8%-2.3% 
$4.45-11.9%-0.7%-2.3% 
$4.21-5.7%-0.5%-1.6% 
$4.10-3.1%-0.4%-1.6%...Maintain Average Delay
$3.961.1%-0.3%-1.3% 
$3.853.5%-0.2%-0.8% 
$3.6614.3%0.0%-0.3%...Maintain Average User Costs
    ...Maintain Average Travel Time Costs
Source: Highway Economic Requirements System.

If current funding levels were sustained, and the mix of highway preservation and widening investments recommended by HERS were implemented, then significant reductions could be achieved in average total delay, total user costs and total travel time costs. However, as noted above, spending for additions to existing rural Interstates rose 137.3 percent between 2000 and 2002. If future spending reverts back to a level more in line with what was observed in 2000, then average total delay would be expected to increase.

Urban Interstates

Exhibits 16-17 and 16-18 show the impacts on the same measures of conditions and performance for different levels of capital spending on urban Interstates. Exhibit 16-17 shows that an average annual highway preservation investment of approximately $10.0 billion would be required to maintain average IRI at 2002 levels. As with rural Interstates, the percentage of travel on urban Interstate pavements with good ride quality would increase at this level of investment, while investment would need to increase to over $12 billion to maintain the percentage of VMT on roads with acceptable ride quality.

Exhibit 16-17, projected urban interstate pavement condition in 2022 for different possible funding levels. Line chart with data table. The line chart shows a downward trend for change in average IRI beginning with a 10.1% change in funding at $7.49 billion to a -18.1% change at $20.84 billion average annual investment.
Average Annual Highway
Preservation + Expansion
Investment (Urban Interstates)
Percent Change in Average Percent of VMT
on Roads with
Funding Level Description: Investment Required to...
(Billions of 2002 Dollars)IRIIRI<95IRI<170 
$7.46 45.6%90.0%2002 Values
$20.84-18.1%72.7%93.7% 
$18.20-16.6%70.7%93.0% 
$16.47-14.5%68.9%92.2% 
$15.12-13.0%67.2%91.8% 
$13.80-10.5%64.5%91.1%...Maintain VMT with IRI<170
$11.92-6.2%61.0%89.7% 
$10.96-3.2%57.5%89.0% 
$10.18-1.1%55.4%87.9%...Maintain Average IRI
$9.750.1%54.3%87.6% 
$8.834.0%51.6%86.1% 
$7.4910.1%47.8%81.8% 
Source: Highway Economic Requirements System.

If current funding levels were sustained, and the mix of highway preservation and widening investments recommended by HERS were implemented, then average IRI on urban Interstates would be expected to increase by 10.1 percent, and the percent of VMT on roads with acceptable ride quality would fall to 81.8 percent. The results suggest that a substantial increase in urban Interstate investment would be necessary to prevent average pavement condition on urban Interstates from deteriorating in the future.

Exhibit 16-18 indicates that an average annual investment level in highway preservation and capacity expansion of between $9.75 and $10.18 billion would be needed to maintain average delay on urban Interstates. Total user costs would be maintained at investment levels up to $10.96 billion, and travel time costs on urban Interstates would be maintained at funding levels over $12 billion. These amounts are 30 to 70 percent higher than the comparable 2002 funding level of $7.5 billion. The results suggest that, if average annual funding were maintained (in constant dollars) at 2002 levels through 2022, average delay on urban Interstates would increase by 9.6 percent, total user costs would increase by 4.1 percent, and travel time costs would increase by 9.6 percent.

Exhibit 16-18, projected urban interstate conditions and performance in 2022 for different possible funding levels. Line chart with data table. The line chart shows a downward trend for change in average delay beginning with a 9.6% change in funding at $7.49 billion to a -20.9% change at $20.84 billion average annual investment.
Average Annual Highway
Preservation + Expansion
Investment (Urban Interstates)
(Billions of 2002 Dollars)
Percent Change in Funding Level Description:
Investment Required to...
Average Total DelayTotal User CostsTravel Time Costs
$7.46 2002 Values
$20.84-20.9%-5.9%-6.8% 
$18.20-17.3%-5.0%-5.3% 
$16.47-14.7%-4.2%-4.0% 
$15.12-12.7%-3.6%-2.9% 
$13.80-9.8%-2.8%-1.7%...Maintain Average Travel Time Costs
$11.92-6.3%-1.4%0.5% 
$10.96-3.6%-0.5%2.0%...Maintain Average User Costs
$10.18-1.5%0.3%3.2%...Maintain Average Delay
$9.750.6%0.7%4.0% 
$8.834.4%1.9%5.9% 
$7.499.6%4.1%9.6% 
Source: Highway Economic Requirements System.

Bridge Preservation

As described in Chapter 7, the National Bridge Investment Analysis System model identifies preservation investment requirements for all bridges, including those on Interstates. The current Interstate bridge preservation backlog is estimated at $14.2 billion.

Exhibit 16-19 describes what the Interstate bridge backlog after 20 years would be at different funding levels. An average annual investment in bridge preservation of $2.13 billion is required so that the Interstate bridge investment backlog would not increase above its current level over a 20-year period. An average annual investment of $2.82 billion would be sufficient to eliminate the existing Interstate bridge investment backlog and correct other deficiencies that are expected to develop over the next 20 years, where it is cost-beneficial to do so.

Exhibit 16-19 Projected Interstate Bridge Investment Backlog in 2022 for Different Possible Funding Levels
(Billions of 2002 Dollars)
Average Annual Investment 2022 Interstate Bridge Backlog
$2.82$0.0
$2.65$3.9
$2.50$6.7
$2.27$11.2
$2.13$14.2
$1.96$17.7
$1.65$24.2
$1.38$31.1
Source: National Bridge Investment Analysis System.

Exhibit 16-13 indicates that bridge preservation expenditures on Interstates totaled $3.2 billion in 2002. Thus, if this level of funding were maintained in constant dollars over 20 years, NBIAS projects that the Interstate bridge backlog could be eliminated. However, Exhibit 16-14 shows that Interstate bridge preservation spending rose 93.7 percent from $1.6 billion to $3.2 billion between 2000 and 2002. If future spending reverts back to a level more in line with what was observed in 2000, then the Interstate bridge preservation backlog would increase significantly.

Current Spending Versus Investment Requirements

Exhibits 16-15 through 16-19 indicate that 2002 levels of highway preservation and system expansion investment on rural Interstates are above the levels necessary to maintain conditions and performance in the future, although there remain significant opportunities for cost-beneficial improvements to the system. The 2002 level of rural and urban Interstate bridge preservation investment would be adequate to address the economic backlog of bridge deficiencies, if that level of investment could be sustained. However, as shown in Exhibit 16-14 and discussed previously, 2002 may represent an unusually high year for rural Interstate capital spending, especially for rural bridges.

On urban Interstates, significant increases in funding for preservation and expansion above current levels would be required to prevent both average physical conditions and operational performance from becoming degraded.

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