Conditions and Performance Chapter Listing

Conditions and Performance Home Page

Introduction

Summary

Road Conditions

Bridge Conditions

Transit System Conditions

Pavement Terminology & Measurements

Pavement condition affects travel cost including vehicle operation, delay and crash expenses. Poor road surfaces cause additional wear or even damage to vehicle suspensions, wheels, and tires. Delay occurs when vehicles slow for potholes or very rough pavement. In heavy traffic, such slowing can create significant queuing and subsequent delay. Unexpected changes in the surface condition can lead to crashes and inadequate road surfaces may reduce road friction, which affects the stopping ability and maneuverability of vehicles.

The pavement condition ratings in this section are derived from one of two measures: International Roughness Index (IRI), and the Present Serviceability Rating (PSR). The IRI measures the cumulative deviation from a smooth surface in inches per mile. The PSR is a subjective rating system based on a scale of 1 to 5. Prior to 1993, all pavement conditions were evaluated using PSR values. Exhibit 3-2 contains a description of the PSR system.

Exhibit 3-2. Present Serviceability Rating

States are now expected to report IRI data for the Interstate system, other principal arterials, and rural minor arterials. IRI reporting is recommended for all other functional systems, but the majority of the data reported on rural major collectors, urban minor arterials, and urban collectors still uses PSR ratings. The FHWA adopted the IRI for the higher functional systems because this index uses a standardized procedure, is consistent across jurisdictions, is an objective measurement, and is accepted as a worldwide pavement roughness measurement. The IRI system results in more consistent data for trend analyses and across jurisdictions.

Exhibit 3-3 contains a qualitative pavement condition term and corresponding quantitative PSR and IRI values. Interstate mileage has stricter guidelines than all other functional systems under both PSR and IRI. The translation between PSR and IRI is not exact. The IRI values are based on objective measurements of pavement roughness, while PSR is a more subjective evaluation of a broader range of pavement characteristics. For example, a given Interstate pavement section could have an IRI rating of 165, but might be rated a 2.5 on the PSR scale. Such a section would be rated as "Mediocre" based on its IRI, but would have been rated as "Poor" had PSR been used. Thus, the mileage of any given pavement condition category may differ depending on the rating methodology. The historic pavement data in this report only go back to 1993, when IRI data began to be collected. Caution should be used when making comparisons with older data from earlier editions of this report.

Exhibit 3-3. Relationship Between IRI and PSR

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 National Highway System (NHS) mileage should meet pavement standards for "acceptable ride quality." This goal is discussed in greater detail in Appendix B. In order to be rated "acceptable" pavement performance must have an IRI value of less than or equal to 170 inches per mile. The FHWA Strategic Plan applies the same ride quality standard to all NHS routes, including those off the Interstate system. IRI is required to be reported for all NHS routes, so the PSR data are not used to determine "acceptable ride quality" in the Strategic Plan or related annual reports. This report uses the term "less than acceptable" (< Acceptable) to describe mileage that does not meet the "acceptable" threshold on the Interstate system.

In this chapter, overall pavement condition is presented based on the qualitative condition terms "very good," "good," "fair," "mediocre" and "poor" associated with the IRI or PSR system. Pavement conditions specific to the NHS are discussed in Appendix B.