This year marks the 51th anniversary of Highway Statistics, an annual publication produced by the Office of Highway Information Management (OHIM), Office of Policy Development, Federal Highway Administration (FHWA). Highway Statistics is a compilation of analyzed statistics of general interest on motor fuel; motor vehicles; driver licensing; highway-user taxation; state highway finance; highway mileage; federal aid for highways; and prior year highway finance data for municipalities, counties, townships, and other units of local government. Starting with the 1992 edition, a section on international data was included. Periodically, special study data, such as the Nationwide Personal Transportation Surveys, are included. In the 1993 edition, which reported 1992 data, a metric section was also established.

Early on, a summary report entitled Summary to 1945 was published; that series has been continued every decade. This publication includes the most used data going back as far as that particular data was collected. It has been a valuable tool for data users in preparing trend and forecasting charts. Summary to 1995 will be available by mid-1997.

Highway Statistics (or the Yellow Book as many refer to it) has made great strides during its 51-year existence. Throughout its history, Highway Statistics has changed with the times, always striving to increase its information value, improve the quality of its presentation, and expand its accessibility to the public. As we enter the information-superhighway age, we will still strive to make Highway Statistics the standard in transportation data. Already significant portions of its content are electronically available through the American Association of State Highway and Transportation Officials' Comprehensive Transportation Information Planning System (CTIPS) and in several locations over the Internet. Highway Statistics 1994 and Highway Statistics 1995 (and Summary to 1995 in mid-1997) may be viewed or downloaded from the Internet (http://www.cti1.volpe.dot.gov/fhwa).

History of Data Collection

The collection of highway data and its distribution began as early as 1892. In 1893, the secretary of agriculture established the Office of Road Inquiry (ORI) with an appropriation of $10,000, and thus began the predecessor of FHWA. ORI in 1904 inventoried all the roads in the United States outside of the cities. Through questionnaires mailed to the county officials, the investigation went far beyond merely tabulating road mileage. This inventory also gathered information about taxation and sources of revenue, road laws, and total expenditures in every county of every state. This report was published in 1907, and Table 1 displays the 1904 results as compared to the 1995 data.

Although ORI was limited in those days to the mere collection of data, that concept has changed dramatically over the years. The process has been continually refined to reflect the changing needs and expectations of our transportation system. Through a publication produced by OHIM, A Guide to Reporting Highway Statistics, the collection of data has been structured to ensure consistent and regular updating of information. The guide consolidated 16 separate reporting forms and instructions for highway-related data on motor-fuel consumption, motor-vehicle registration, driver licensing, and the sources and funding of state and local government highway programs. The guide promotes a unified reporting concept with an understanding of interrelationships among different reporting areas. Reporting procedures contained in the guide are not rigid standards; rather, they represent a reporting reference system that FHWA recommends the states use to collect and report state and local highway data to FHWA. The reporting of data that measures and monitors the condition, performance, use, and operating characteristics of the nation's highways is regulated by a companion program entitled the Highway Performance Monitoring System (HPMS). 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.

It cannot be emphasized too strongly that the success of FHWA's statistical program is a result of the long partnership between FHWA and the state departments of transportation (DOTs). FHWA depends on the state DOTs to coordinate the data collection from a multitude of agencies and local jurisdictions.

Purpose of the FHWA Statistical Program

FHWA collects data from the states and then publishes in Highway Statistics the 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; calculating and evaluating federal fund apportionments; keeping state governments informed; and, in general, as an aid to highway planning, programming, budgeting, forecasting, and fiscal management. Another use is the extensive evaluation of federal, state, and local highway programs. Although the information in Highway Statistics meets the federal need of providing a national perspective on highway program activities, other users need to exercise care in using this information for other purposes.

Information published in Highway Statistics comes from a number of sources. These sources include various administrative agencies within the 50 states, more than 30,000 units of local governments, FHWA, other federal agencies, and the five U.S. territories.

As mentioned previously, information included in Highway Statistics is the result of a cooperative effort between FHWA and the states. Nearly all of the data provided to FHWA, including the HPMS data, come through state DOTs from existing databases or business records of many individual state and local governmental agencies, including metropolitan planning organizations (MPOs). The existing databases 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 databases 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 that are collected solely for 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.

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, highway statistical information is not necessarily comparable across all states. For many of the data items reported in Highway Statistics, a user should not expect to find consistency among all states because of 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, percentage of 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 the user chooses to compare state data, he must be prepared to carefully select a set of states that have similar characteristics related to the specific comparison being made. 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 must be considered. A faulty selection is likely to yield invalid data comparisons. Both the 1994 and 1995 editions of Highway Statistics have a two-page "Peer State" table that lists some of these characteristics so that the data user may be made more aware of possible problems that could arise when comparing state-by-state data.

Table 2 shows a simple listing of four adjoining southern states with various attributes demonstrating why special consideration should be given by the user when comparing state-to-state data. Notice that although Mississippi is one of the southern adjoining states, it is more rural than the other three states.

Mary K. Teets is a program analyst in the National Data Management and Dissemination Division, Office of Highway Information Management, Federal Highway Administration. Ms. Teets has been the editor of Highway Statistics since 1991.