Conditions and Performance Chapter Listing

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Introduction

System Conditions

The Federal Highway Administration 1998 National Strategic Plan introduced a new descriptive term for pavement condition, "acceptable ride quality." The Strategic Plan stated that by 2008, 93 percent of the NHS mileage should meet pavement standards for "acceptable ride quality." In order to be rated "acceptable" pavement must have an International Roughness Index (IRI) value less than or equal to 170 inches per mile. As shown in Exhibit B-3, the percentage of NHS miles with acceptable ride quality has increased each year from 1993 to 1995, improving from 88.7 percent to 91.7 percent.

Exhibit B-3

Percentage of NHS Miles with Acceptable Ride Quality, 1993-1997

Exhibit B-4 presents information on NHS pavement condition, using the five categories (poor, mediocre, fair, good, very good) discussed in Chapter 3. In that chapter, different standards were applied to Interstate and non-Interstate highways for categorizing pavement, as described in Exhibit 3-3. In Exhibit B-4, the Interstate standards were applied to all NHS sections, regardless of functional class, so that all sections that did not meet the Strategic Plan standard for acceptable ride quality would be classified as "poor." Therefore, some non-Interstate NHS sections that were classified as "fair" in Chapter 3 would be classified as "mediocre" in this Appendix. Also, all non-Interstate NHS sections classified as "mediocre" in Chapter 3 are identified as "poor" in this Appendix.

Exhibit B-4. 1997 National Highway System Percent Miles by Pavement Roughness Category

Rural NHS routes tend to have better pavement conditions than urban NHS routes, which is consistent with the results reported for all roads in Chapter 3. The percent of poor pavement for rural NHS routes is 5.3 percent, compared to 16.4 percent in NHS routes in urban areas. The Interstate component of the NHS tends to have better ride quality than the non-Interstate component. Pavement condition on the NHS improved between 1995 and 1997, as described in Exhibit B-5. The percent of pavement in poor, mediocre or fair condition fell from 60.3 percent to 54.4 percent. The percent of pavement in good or very good condition rose from 39.8 percent to 45.7 percent.

Exhibit B-5. Comparison of 1995 and 1997 Pavement Condition on the NHS

Bridge Conditions

Bridge deficiency data are not yet available for the designated NHS. Exhibit B-6 contains information on bridge deficiencies for the interim NHS (including all Interstate and Other Principal Arterials). From 1996 to 1998 the share of total bridges that were deficient fell from 25.8 percent to 23.1 percent. Structural deficiencies fell from 7.6 percent to 6.9 percent, while functional deficiencies declined from 18.2 percent to 16.2 percent. Deficiencies in both rural and urban areas declined.

Exhibit B-6. Interim NHS Bridge Deficiencies

The Federal Highway Administration 1998 National Strategic Plan established a target to reduce the percentage of NHS bridges that are classified as deficient to 20 percent by 2008. As shown in Exhibit B-7, the percentage of bridge deficiencies on the NHS has declined from 1994 to 1998 from 25.8 percent to 23.1 percent.

Exhibit B-7

NHS Bridges: Percent Deficient, 1994-1998

Most of the reduction in the percent of bridge deficiencies occurred between 1996 and 1998. While structural deficiencies declined each year from 1994 to 1998, the percent of functionally obsolete bridges rose from 1994 to 1996, before declining in 1997.