This section contains data on the physical, operational, usage characteristics, extent, and performance of public roads existing in the United States as of December 31, 1994.
EFFECTS OF CHANGES IN DATA REPORTING PROCEDURES
The current data are based on the Highway Performance Monitoring System (HPMS). The HPMS comprises a combination of sample data on the condition, use, performance and physical characteristics of facilities functionally classified as arterials and collectors (except rural minor collectors); certain condition and use data for all rural arterials and urban principal arterials; and system-type data for all public road and street facilities within each State. When a State fails to provide current year data (or complete current year data), various means are used to prepare information that is reasonably current. Where this is true, the States may have provided current aggregate area wide totals and the included tables have used these data to the extent possible. Footnotes have been included where appropriate to explain missing data or data which have been estimated from previously available data.
It is important to note that the roadway extent, characteristics, and performance data contained in this publication represent a transition period between the pre- and post-Intermodal Surface Transportation Efficiency Act (ISTEA) of 1991. To be specific, the current data reflect the majority of the States' implementation and use of adjusted 1990 Census urbanized area boundaries and functional reclassification. This plays a significant role regarding the extent of mileage identified as rural, small urban, or urbanized, and for the related functional systems classification.
ORGANIZATION OF MILEAGE AND TRAVEL TABLES
Almost all tables in this section contain rural and urban breakouts where urban is further broken down into small urban (5,000 to 49,999 population) and urbanized (> 50,000 population).
An urbanized area is an area with 50,000 or more persons that encompasses at a minimum the land area delineated by the Bureau of the Census. The Bureau of the Census establishes urbanized area boundaries based on the density of the population (1,000 persons per square mile). The adjusted Census urbanized area boundary reflected in this publication is usually enlarged to include such additional areas as airports, satellite cities/towns, strip development adjacent to high-use roadways, and other areas and facilities that are important to or serve the urbanized area. In some cases, the adjusted urbanized area includes land that will become urban in some predetermined amount of time (such as 35 years). These boundaries are decided upon by State and local officials with the approval of the FHWA.
The tables in this section have been organized into seven general areas:
All tables in this publication include only mileage classified as public road mileage in accordance with 23 U.S.C. 402. Table HM-10 contains the total public road mileage of roads and companion travel table, VM3. Table HM-16 is a nationwide aggregate table which contains mileage of Federal-aid highways by jurisdiction. Another nationwide aggregate table, HM18, contains mileage of Federal-aid highways by functional system, and includes small urban and urbanized area summaries as well as total urban. Table HM20 contains all public road mileage by State, by functional system. This table is in the same format as table VM-2 and contains the mileage that corresponds to the travel contained in that table.
The increase in total road and street mileage by construction is relatively small each year. Most construction is for the improvement of existing highways and streets, such as resurfacing those previously surfaced, widening pavements, reducing grades, minimizing curves, eliminating grade crossings, and other improvements that provide safer, more efficient highways having greater traffic and load-bearing capacities. Most new mileage falls in the local functional system category that serves residential use. Decreases in public road mileage do occur. In recent years, this has been due to the removal of some timber, forest access, and natural resource roads from public use.
Roads in Federal forests and reservations may be part of the State and local systems and are included with the mileages reported for those systems. Mileage directly under Federal control is identified in tables HM10, HM12, HM14, HM16, and HM50.
The designation of a road or street as a Federal-aid highway does not alter its status as a State or county road or city street. A Federal-aid highway simply means that, because of its service value and importance, it has been made eligible for Federal-aid construction and maintenance funds.
The classification used in the tables identifies only the visible surface types on existing streets and roadways. Many highways, either by original design or because of reconstruction, consist of more than one major type of construction material. No data relative to vertical composition are presented, except for the composite pavement type where the reporting agency has concluded that an original portland cement concrete roadway has been overlaid with one or more inches of compacted bituminous material.
FEDERAL-AID HIGHWAY MILEAGE
Except for minor amounts of Federal highway mileage under the U.S. Forest Service, Bureau of Land Management, Bureau of Indian Affairs, and National Park Service, practically all of the roads and streets in the United States are under the jurisdiction of State and local governments. The Federal-aid highways are, basically, segments of State and local systems mileage eligible for Federal aid. Except under special circumstances, this excludes roads that are functionally classified as rural minor collector or rural and urban local.
The Intermodal Surface Transportation Efficiency Act (ISTEA) of 1991 eliminated the historical Federal-Aid Systems and created the National Highway System (NHS) and other Federal-aid highway categories. The interim NHS established under ISTEA consists of the entire principal arterial system. (For purposes of this publication, the NHS excludes any nonhighway routes, i.e., ferry boat routes.) After September 30, 1995, no more NHS and Interstate System Maintenance Program funds may be apportioned unless legislation is enacted that formally designates an NHS. As directed under Section 1006 of ISTEA, a proposed NHS was prepared in consultation with appropriate local officials and submitted to the United States Congress.
All historical tables linked to the superseded Federal-Aid Systems have been changed to reflect the interim NHS (the interim NHS includes all facilities functionally classified as principal arterial), and other Federal-aid highways, as applicable. These include tables HM14, HM15, HM16, HM18, the HM30 series, HM41, VM3, and the FI series. Table HM-43, which had many references and ties to the now defunct Federal-Aid Primary System, has been eliminated.
Because the proposed NHS (if officially adopted by Congress via future legislation) could affect the Federal-aid highway categories, a series of "P" tables has been included to reflect such potential change. The "P" tables duplicate all of the historical Federal-aid tables in format only. A few additional tables have been provided in the "P" series for supplemental information. The data contained in the "P" series should be considered as preliminary and illustrative of the future NHS. Table HM30P is the only table in this section containing both open-to-traffic and known future (not open) Federal-aid highway mileages.
The Eisenhower National System of Interstate and Defense Highways was originally established by the Federal-Aid Highway Act of 1944. The Federal-Aid Highway Act of 1956 and the companion Highway Revenue Act of 1956 further defined the purpose and extent of the system and, as subsequently amended, dedicated a group of Federal excise taxes on motor fuel and automotive products to the support of Federal-aid highway activities. By law, the Interstate System is limited to 42,500 miles under Section 103 of Title 23 and other routes incorporated under Section 139(a) of Title 23 that are logical additions or connections and meet Interstate System design standards. The Interstate System under Section 139© is limited only to Alaska and Puerto Rico.
The Interstate System connects, as directly as practicable, the Nation's principal metropolitan areas, cities, and industrial centers; serves the national defense; and connects at suitable border points with routes of continental importance.
The Federal-aid highway mileages are classified according to system, surface type, lane width, traffic lanes, access control, and traffic volume in tables HM-31 through HM39. The categories for a given data item vary within each table to provide representation of the characteristics of the particular Federalaid highway category.
Count of bridges
Table HM-41, Highway Bridges Greater Than or Equal to 20 Feet, contains a count of the bridges from the Structure Inventory of the Nation's Bridges by Federal-aid highway category for rural and urban areas. Its companion table, HM65, is similar except that the bridge counts are for rural and urban functional systems.
MILEAGE BY FUNCTIONAL SYSTEM
The functional systems used in tables HM50 through HM80 result from the assignment of streets and highways into groups according to the character of service they are intended to provide. Because most travel involves movement through a network of roads, individual roads and streets do not serve travel independently in any major way. Functional classification defines the role that a particular road or street plays in serving the flow of trips through a highway network. The functional systems are: (1) arterial highways, which generally handle the long trips, (2) collector facilities, which collect and disperse traffic between the arterials and the lower level, and (3) local roads and streets, which serve the land access function to the residential areas, individual farms, and other local areas. The functional system mileages are identified by jurisdiction, surface type, lane width, traffic lanes, access control, and traffic volume in tables HM-50 through HM59.
Table HM-60 contains estimated rural and urban lane mileage by functional system. FHWA assumed two lanes for rural minor collector and urban and rural local functional system lane mileage estimate.
Volume-service flow ratio
Table HM-61 contains the mileage for each rural and urban arterial and collector (except rural minor collector) functional system by State for various ranges of volume-service flow ratio. These data are expanded from the traffic volume and peak service flow (capacity, as defined by the 1985 Highway Capacity Manual) data reported on or calculated from other data in the HPMS sample sections, and are a useful measure of traffic congestion existing on the States' functionally classified facilities.
Table HM-63 contains mileage that uses the present serviceability rating (PSR) or the international roughness index (IRI), as reported in HPMS, to group the data into various categories of pavement condition. Because of higher standards, the ranges of PSR and IRI for the Interstate System vary slightly from the ranges for the other functional systems.
The PSR is a numerical value ranging from zero to five, reflecting poor pavement condition at the lower end of the scale and very good pavement condition at the higher values. If PSR has been carefully monitored, it should provide a useful basis for rating roadways within a State. Generally, PSR is a subjective rating scheme and because of the various methodologies used by the States to collect these data, PSR may not be consistent or comparable among the States. For this reason and because traffic, weather, soil conditions, etc., vary, rankings of the States' pavements based on PSR should be avoided.
Measured pavement roughness is an objective equipment-based rating reported in the HPMS as IRI in inches per mile. These ratings are collected by various mechanical devices, some of which may require calibration through correlation to "known profiles" established via precise measurements. The IRI is a numerical value that is an accumulation of the inches of vertical movement of a vehicle over a roadway surface, adjusted to reflect the rate per mile. Low values indicate a smooth riding quality, while higher values are indicative of a rough road. Because IRI is an objective mechanically measured index, IRI should be more consistent across State lines when measuring similar surface textures and when proper measuring device calibration procedures have been followed by the State highway agencies.
Because PSR is subjective and may be inconsistent among the States, and because IRI should be a more consistent measure of pavement condition, table HM-63 is being changed over to be IRI-based, at least for the principal arterial and rural minor arterial systems. Table HM-64 contains only IRI for the higher systems. FHWA believes that pavement condition data are getting better with increased measurement, reporting and use of IRI data.
As additional pavement roughness/IRI data protocols become available for IRI equipment and measurement, such as filtering, measurement intervals, sensor use, etc., and are developed and adopted by the States, IRI comparability among State data should continue to improve. As in the past when FHWA implemented the recommendation of State pavement and planning officials to incorporate IRI into the HPMS data base, FHWA will continue to rely upon State activities such as the Road Profiler Users Group and research for standardization in the form of pavement roughness protocols. Considerable research of this nature is planned by or underway for FHWA's Pavement Division.
Minor collector and local functional systems
Table HM-67 contains estimates of minor collector and local functional systems mileage by average daily traffic volume and surface type for rural and urban areas. Estimates are supplied by the States in the area wide (aggregate) portion of the HPMS data submittals.
Urbanized area mileage, travel, and other characteristics
Table HM-71 contains mileage and daily travel data by functional system for adjusted Census urbanized areas having a population of 50,000 or more persons. The daily travel contained in this table times 365 days (366 days for leap years) would equal annual travel. Table HM72 contains rate and characteristic type data that are based on the State-reported mileage, travel, population, and net land area aggregate data for the same urbanized areas. An estimate of freeway lane mileage (including the Interstate System) in each urbanized area is also provided; it is based primarily on the HPMS universe data. Where urbanized areas cross State boundaries, the tables contain information for the entire area without regard to State boundaries.
State highway agency-administered mileage
State highway agency-administered (jurisdiction) mileage by functional system, based on the HPMS universe data, is contained in table HM80. Lane mile, daily vehicle-miles traveled, and annual average daily traffic per lane of road estimates are provided in the companion table HM81. These estimates are derived based on the HPMS universe information.
HIGHWAY USAGE CHARACTERISTICS
Table VM-1 contains the estimated travel for the current year (1994) and revised figures for the previous year (1993) for passenger cars, motorcycles, buses, and trucks for the rural Interstate System, other rural arterial roads, other rural roads, urban Interstate System, and other urban streets. The rural and urban street categories are based on a summary of highway functional systems contained in table VM-2. The vehicle types are based on a summary of vehicle distributions as shown in the VM-4 series. These distributions are normalized to account for temporal variation. The other rural arterial roads category includes all other principal and minor arterials, excluding the Interstate System. The other rural roads category includes the collector and local functional systems. All urban systems except the urban Interstate System are included within the other urban category.
Table VM-1 also contains the number of vehicles registered by type by total fuel consumption. Also included are the calculated annual average distance traveled, average distance traveled per gallon, and average fuel consumption for each vehicle type. The highway use of motor fuel and the motor-vehicle registrations contained in tables MF-21 and MV-1 are used to obtain the related items of average distance traveled per vehicle, average fuel consumption per vehicle, and average distance traveled per gallon of fuel consumed. In addition, table VM-1 contains FHWA's estimate of distance traveled per person based on the most current information from the Nationwide Personal Transportation Study, the Truck Inventory and Use Survey, and the National Transportation Statistics report.
Table VM-2 contains a summary of the States' estimated highway travel based on traffic counts taken along selected highway sections which are grouped into categories, or functional systems, according to the character of service they provide. It is a companion table to table HM-20.
Table VM-3 contains the estimated highway travel carried by Federal-aid highways. It is a companion to the mileage table HM-15 and has combined certain functional system travel values as indicated at the front of this section's text.
The VM-4 series first appeared in the 1993 edition of Highway Statistics. It describes distribution of travel activity by vehicle type by arterial functional systems. Data in some cases may exclude motorcycles, combine some vehicle types, and/or be limited in count duration and seasonal coverage. Analysts are cautioned to refer to the individual tables in using this data for comparison.
The FI series contains the total fatal and nonfatal injury accidents along with the total numbers of fatalities, most seriously injured persons, total nonfatal injuries, and corresponding rates for all highways in each State. Fatality data are based on the 30-day definition; i.e., only accident victims who die within 30 days of their accidents are counted as fatalities. The tabulations also contain numbers and rates (per 100 million vehicle miles) of accidents and casualties on the functional systems and Federal-aid highway categories.
Table TC-3, along with the graph, Comparison of Growth in Volumes and Loadings on the Rural Interstate System, display the interrelationship among vehicle types, volumes, and axle loadings. The data, which are from the Truck Weight Study, are collected by the States for varying periods of time and are not adjusted to typify annual system averages. The data for passenger cars, buses, and light single-unit trucks have been combined in table TC-3.
The graph, Comparison of Growth in Volumes and Loadings on the Rural Interstate System, portrays the rapid growth in loadings relative to volumes. The data points on the graph are 3year moving averages. It should be noted that the increase in loadings is a function of increased axle weights as well as an increase in the number of trucks.
USE OF DATA
Readers are cautioned to refer to the previous paragraphs as well as all footnotes contained on each table prior to using the data in this section.