Conditions and Performance Report

Conditions and Performance Report
Chapter 9—Impacts of Investment

Conditions and Performance Chapter Listing

Conditions and Performance Home Page

Introduction

Impact of Highway and Bridge Investment on Conditions and Performance

Transit Investment Impacts

Methods for Increasing Future Investment for Transportation Projects

Recent Condition and Performance Trends Versus Spending Trends

Chapter 6 indicated that there has been a change in the types of highway capital improvements being made in recent years. The percentage of total highway capital outlay used for the construction of new roads and bridges dropped from 22.8 percent in 1993 to 15.2 percent in 1995, rising back to 15.6 percent in 1997. The percentage used for system preservation rose from 44.7 percent to 50.0 percent in 1995, falling back to 47.6 percent in 1997. Over this 4year period, highway capital outlay has grown 2.2 percent in constant dollar terms.

Conditions

The improved highway and bridge conditions reported in Chapter 3 reflect the effects of this shift toward system preservation, and the constant dollar increase in investment. From 1993 to 1995, the percentage of all road miles in poor condition fell from 8.6 percent to 6.4 percent. From 1995, as the percentage of resources devoted to system preservation dipped, the percentage of all road miles in poor condition rose from 6.4 percent to 6.6 percent. The percent of deficient bridges has been reduced each year during this 4-year period, falling from 32.5 percent to 29.6 percent.

Q Are the recent trends in condition and performance consistent with the "gap" identified in Chapter 8 between current funding and the Cost to Maintain Highways and Bridges?

A As indicated in Chapter 8, bridge spending has exceeded the investment requirements for the bridge component of the Cost to Maintain in recent years. This is consistent with the recent decline in the percent of deficient bridges.

Recent highway spending has been below the investment requirements for the highway component of the Cost to Maintain. Average IRI and the percent of pavement in poor condition have both worsened since 1995, though they have improved since 1993.

Chapter 7 discussed the existence of a backlog of pavement improvements that would currently be cost-beneficial to address. As indicated in Chapter 8, some of these deficiencies could be addressed relatively inexpensively in the short term, but will become much more expensive to correct if they are deferred. While current funding levels have been adequate to gradually improve pavement ride quality, continuing this level of investment indefinitely would not allow some pavement deficiencies to be addressed, and would ultimately be expected to drive up the long term cost of keeping average conditions at 1997 levels.

Operational Performance

Highway operational performance since 1993 has been mixed, depending on which indicator is used. As indicated in Chapter 4, from 1993 to 1995, average delay in urbanized areas greater than 200,000 in population increased from 11.9 hours to 13.7 hours per thousand VMT. From 1995 to 1997, average delay in urbanized areas fell to 13.0 hours per thousand VMT. The percentage of urban Interstate travel on segments with a V/SF>=0.80 increased from 52.6 percent in 1993 to 53.3 percent in 1997. However, congested travel on other urban principal arterials declined. Traffic density, measured as DVMT per Lane-Mile, increased on all functional systems between 1993 and 1997.

Between 1993 and 1997, the percentage of capital outlay used for system expansion (including new roads, new bridges, and new lanes on existing roads and bridges) fell from 49.4 percent to 44.4 percent. At the same time, spending for traffic operational improvements increased. System expansion and traffic operational improvements both tend to increase capacity and reduce congestion. Since traffic density measured by DVMT per Lane-Mile has been increasing steadily, but overall delay and the V/SF ratios have not gotten substantially worse, this implies that existing roadways are being utilized more effectively. Part of this is the result of increased investment in traffic operational improvements, which add capacity without adding additional lane-miles. Some of this is also the result of changes in driver behavior.

Q How do the conditions and performance of Interstate routes with heavy truck traffic compare to those with fewer trucks?

A Approximately 20 percent of Interstate mileage has truck traffic that exceeds 30 percent of total traffic on these routes. Exhibit 9-5 compares the percent of pavement with acceptable ride quality and the percent of congested travel for Interstate routes with 30 percent or more trucks with those with lighter truck traffic. As indicated in Chapter 3, to meet the FHWA Strategic Plan standard for acceptable ride quality, pavement must have an IRI value of 170 or less. In this exhibit, congested travel includes sections with a V/SF ratio of 0.80 or higher.

This exhibit shows that on the Interstate pavement is in better condition on routes with high truck travel than on those with fewer trucks, and the portion of miles with smooth pavement increased from 1993 to 1997. While heaver vehicles cause more damage to pavement than lighter vehicles, routes most used by trucks are typically those with pavement with a higher strength than average, and that receive more than average attention from the appropriate jurisdictions for rehabilitation and maintenance.

The exhibit also shows that there is less congestion on routes with a high percentage of truck travel, but that the congestion varies from year to year. Truck drivers chose routes with less congestion when feasible. (See Exhibit 9-5)

Exhibit 9-5. Conditions and Performance of Interstate Routes with Heavy Truck Traffic

Return to top

Page last modified on November 7, 2014