For Users of Highway Statistics

Purpose of Information

The Federal Highway Administration (FHWA) collects from the States and publishes in Highway Statistics information necessary to support its responsibilities to the Congress and the public. This information is used in the development of highway legislation at both the Federal and State levels. The information is also used in preparing legislatively required reports to Congress, in calculating and evaluating Federal fund apportionments, in keeping State governments informed, and, in general, as an aid to highway planning, programming, budgeting, forecasting, and fiscal management. It is also used extensively in the evaluation of Federal, State, and local highway programs. From an FHWA perspective, the information in Highway Statistics meets the Federal need of providing a national perspective on highway program activities very well. Since this information was developed primarily to meet FHWA and State needs in administering the Nation's highway programs, other users need to exercise thoughtful care in using this information for other purposes.

Quality Considerations

Information published in Highway Statistics comes from a number of sources. These sources include various administrative agencies within the 50 States, over 30,000 units of local government, the FHWA, other Federal agencies, and the five U.S. territories.

Information included in Highway Statistics is the result of a cooperative effort between the FHWA and the States. Nearly all of the data provided to FHWA, including the Highway Performance Monitoring System (HPMS) data, come through State Departments of Transportation from existing data bases or business records of many individual State and local governmental agencies, including metropolitan planning agencies (MPOs). The existing data bases and record keeping systems of these governmental units were designed and are maintained to meet their individual business needs.

Data quality and consistency of information published in Highway Statistics are, therefore, dependent upon the programs, actions and maintenance of sound data bases by numerous data collectors, manipulators and suppliers at the State, local and metropolitan area levels. In general, specific data items that are used by the collecting agency are likely to be of better quality than data items which are collected solely for the FHWA. Data quality and consistency are also dependent upon the nature of the individual data items and how difficult they are to define, collect, etc.

HPMS data are collected in accordance with the Highway Performance Monitoring System Field Manual for the Continuing Analytical and Statistical Database. This document contains standard codes for the various data items to be reported in a consistent format.

Highway statistical data other than the HPMS are collected in accordance with A Guide to Reporting Highway Statistics (the Guide). Reporting procedures contained in the Guide are not rigid standards; rather, they represent a reporting reference system that the FHWA recommends the States use in collecting and reporting State and local highway data to the FHWA.

Nearly all of the State reported data are analyzed by FHWA for consistency and for adherence to reporting guidelines. In a number of cases, data are adjusted to improve consistency and uniformity among the States. The analysis and adjustment process is accomplished in close working relationship with the States supplying the data.

Using Data for Comparisons

Even when data are consistently collected and reported, users need to recognize that highway statistical information is not necessarily comparable across all States or from year to year for a particular State. For many of the data items reported in Highway Statistics, a user should not expect to find consistency among all States, due to many State to State differences. When making State level comparisons, it is inappropriate to use these statistics without recognizing those differences that impact comparability.

Use of reported State maintenance expenditures provides a clear example. Maintenance expenditures per mile can vary between States depending upon a number of factors including differences such as climate and geography, how each State defines maintenance versus capital expenditures, traffic intensity and percent trucks, degree of urbanization, types of pavement being maintained, and the level of system responsibility retained by the State versus that given to other levels of government. It would be inappropriate, therefore, when using data from Highway Statistics to compare per mile maintenance costs across all States to draw any conclusions without taking into account the differences that should be expected in these parameters based upon differing State conditions.

If choosing to compare State data, the user must be prepared to thoughtfully select a set of peer States that have similar characteristics in relationship to the specific comparison being made. Improperly selected peer States are likely to yield invalid data comparisons.

Differences that the user needs to consider in determining suitability of peer States for data comparison purposes include characteristics such as urban/rural similarities, population density, degree of urbanization, climate, geography, differing State laws and practices that influence data definitions, administrative control of the public road system, similarity of the basic State economies, traffic volume similarities, and the degree of State functional centralization.

To facilitate the selection of peer States for possible comparative purposes, a table listing a number of data items which might be considered follows this discussion. Most of these data items are available in other tables in Highway Statistics, but are included here for the user's convenience. Finally, additional special considerations that the user should be aware of in using the information in Highway Statistics are included

in the discussion that precedes each of the individual data sections.

In examining the trends over time for a particular State, the user needs to be aware of any special circumstances that would effect the suitability of trend line comparisons. Hurricanes, blizzards, earthquakes and floods are examples of natural disasters that cause changes in expenditures and funding priorities during the year of the event and in subsequent years. A State's construction season is directly affected by climate conditions with a severe winter restricting the length of the construction season. The initiation or completion of a major construction project changes a number of data trends that could be examined. The user needs to consider how changes in materials, technology, inflation, and a number of other factors affect a State's trend lines.