Global trade, population growth, and other factors are driving large increases in heavy trucks and other traffic on many of the nation’s highways. This traffic growth has accelerated rates of pavement and other roadway deterioration, particularly on the Interstate Highway System, and increased the significance of declining service levels as a drain on the nation’s economic vitality. At the same time, demands for on-time delivery of goods; personal mobility; and a safe, reliable, and environmentally responsible highway system have raised system maintenance costs and increased public dissatisfaction with service disruptions associated with highway repair and reconstruction. Limited funds make it difficult for many agencies to ensure adequate maintenance of their highways. The development of nationwide service levels for the Interstate Highway System would provide benchmarks that departments of transportation (DOTs) and other responsible agencies can use to assess their Interstate maintenance and preservation needs.
The nation’s substantial investment in the Interstate System is embodied in major assets that the states must maintain, including (a) pavements; (b) bridges and other structures (for example, retaining walls, large culverts); (c) roadside assets (e.g., right-of-way, fencing, pipes and ditches); (d) rest areas; and (e) traffic operation assets (e.g., signs, signals). Service levels describe the degree to which the highway system generally, and assets in each of these classes in particular, provides customer service, satisfies the demands of system users, and meets the objectives of other stakeholders. (Service level is often used interchangeably with performance.) Specific definitions of service levels for the Interstate can be broadly applied by the states to gauge various aspects of the system’s performance, for example, with respect to
Ride quality – pavement smoothness, safe operating speeds;
Safety – visible signs and pavement markings, safe and secure rest area facilities, pavement skid resistance, functional guardrails;
Operations reliability – incident response time, traffic flow, winter maintenance;
System investment preservation – risk of premature failure, avoidance of excess wear and tear, realization of full service life; and
Energy and environmental quality – smooth traffic flow, controlled runoff.
Service-level indicators are the specific basis for understanding and determining service level for a particular part of the Interstate system, that is, an asset category. Indicators should be consistent to the greatest extent practicable and ideally would be similar nationwide. Indicators of pavement service level, for example, would include roughness. Measures are the specific means for describing how well or poorly an asset is performing. The international roughness index (IRI), for example, is a measure of roughness; a measured value of the IRI less than 60 is accepted by many jurisdictions as evidence of a “very good” or “high” level of service with respect to pavement roughness. Similarly, sign visibility (measured perhaps by high retro-reflectivity, absence of obstruction, and absence of missing signs) would be indicative that traffic operations assets (that is, the signs) are delivering a high service level relative to safety.
Research continues to develop consistent service levels, indicators, and measures to enable states to manage their Interstate system assets more effectively. This research will facilitate benchmarking the performance of Interstate system assets. (The NCHRP 20-24(37) series of projects, for example, are designed explicitely to encourage adoption of common measures and benchmarking to support system management.)
The objectives of this project were to develop (1) a standard way to describe the service level of Interstate Highway System assets and (2) a process that agencies can use to prepare a template for describing service levels. The service levels would include a standard definition, for example, an “A through F” or “1 to 10” scale with descriptive explanation of these ratings in terms that are meaningful to stakeholders, and the specific indicators of service level for major Interstate assets. Service levels and their indicators would be uniformly defined for the Interstate System as a whole, but service-level measures (how indicators are consistently assessed) could vary from one state to another; implementation will entail recommending suitable service-level measures and protocols for measurement and data collection. The results of this research can be utilized by the agencies for assessing and benchmarking the performance of their Interstate highways.
The research began by assessing the current state of practice among transportation agencies regarding Interstate asset service-level measurement, including a review published literature, telephone interviews and in-person discussions, to identify the resources and reports that states use to describe their highway system’s performance. The research team then recommended (1) a scale and definitions of service levels for Interstate system assets, seeking to address concerns of highway users, transportation agencies, and other stakeholders; (2) indicators for service level of major assets, for which consistent measures exist or could be developed and used to establish service benchmarks and thresholds; (3) thresholds for measures that define service levels and guidance on how thresholds (e.g., of quality or acceptability) may be determined; and (4) a template that can be used to assess, analyze, and report Interstate System performance at regional, state, or national levels. The researchers also developed guidance for data collection practices to support performance assessment and actions to accelerate states’ adoption of the service-level principles and template.
The contractor's final report, published as NCHRP Report 677, includes all results from the research. Information about that report is available by clicking here.