The interstate highway system has contributed mightily to the economic growth and quality of life in America. The interstates and other super-highways will continue to contribute to economic growth and improved quality of life if necessary investments are made. In large measure, the interstate highway system has democratized mobility in the United States, providing virtually all Americans with the ability to move quickly to any destination within their communities and to travel throughout the nation, inexpensively, and at whatever time or date they desire.

This report provides an assessment of the manifold benefits of the interstate highway system. Research by leading transportation authorities and standard statistical methods have been used to estimate the impacts of the interstate highway system. The imperative for upgrading the interstate highway system and other super-highways is described and shown to be readily affordable within the capability of present highway user fee revenue.

While it is not typically thought of in this way, the system is in reality a gift from one group of people --- highway users --- to the nation as a whole, which has reaped a gain of at least $6 in benefit for each $1 spent in construction. And that's just the beginning --- there are additional benefits such as higher employment rates and greater economic opportunity that are simply beyond quantification. Fortunately, the group of people who paid for the interstate highway system is sufficiently large that it's difference from the nation as a whole is virtually without distinction. But it is a worthy difference to keep in mind as a backdrop for public policy deliberations over future funding of highways.

It is not an exaggeration, but a simple statement of fact, that the interstate highway system is an engine that has driven 40 years of unprecedented prosperity and positioned the United States to remain the world's pre-eminent power into the 21st century.

The Dwight D. Eisenhower System of Interstate and Defense Highways is in place and celebrating its 40th anniversary, must surely be the best investment a nation ever made. Consider this:

Without a first class system of interstate highways, life in America would be far different --- it would be more risky, less prosperous, and lacking in the efficiency and comfort that Americans now enjoy and take for granted. People would be crowded into more densely packed inner cities, intercity travel would occur less often and be more cumbersome; freight charges would be higher and, as a consequence, so would prices. Vacation travel would be more restricted.

America is a nation on wheels --- they benefit from a freedom of mobility that is unrivaled anywhere in the world. A substantial portion of that mobility is attributable to the Dwight D. Eisenhower System of Interstate and Defense Highways, which celebrates its 40th anniversary in 1996. The interstate highway system, the largest public works program in history, has had an enormous impact on the nation. The interstate highway system has positively influenced economic growth, reduced traffic deaths and injuries, provided substantial benefits to users, and been a crucial factor in the nation's defense.

Background

Early Planning: As automobiles began to democratize mobility in America in the 1920s and 1930s, it became increasingly clear that greatly improved highways would be needed to accommodate the demand. "Super-highways,"

NOTE: The term "super-highway" is used to denote a controlled access (grade separated) roadway with at least four lanes of traffic separated by direction. Super-highways may be toll roads or free (freeways). In most nations, including the United States, "free" super-highways are not really free, in that their construction, maintenance and patrolling costs are paid by highway user fees. grade separated roadways with four lanes of direction-separated traffic, first appeared in the New York City area parkways that opened in the 1920s.

The interstate highway system was first approved by Congress in 1944, but it was not until 1956 that a comprehensive program was enacted to build the system. By this time, it had become apparent that post-war affluence had produced a huge increase in highway demand and that rapidly expanding highway freight movements required a much improved system. Further, in the volatile Cold War era, national defense provided a primary justification for developing a super-highway system to accommodate the quick and efficient movement of military equipment and personnel.

Authorization of the Interstate Highway System: On June 29, 1956, President Eisenhower signed the Federal Aid-Highway Act of 1956, which authorized the interstate highway system (later formally named the Dwight D. Eisenhower System of Interstate and Defense Highways). The Act authorized 41,000 miles of high quality highways that were to tie the nation together. Later, congressional action increased the length to 42,500 miles and required super-highway standards for all interstate highways.

The system was to be completed by 1975. It was conceived as a "pay as you go" system that would rely primarily on federally imposed user fees on motor fuels --- the federal user fee per gallon of gasoline was increased by one cent. The federal user fees would provide 90 percent of the cost of construction with the balance provided primarily by state user fees. The interstate highway system would incorporate approximately 2,000 miles of already completed toll roads.

High standards were adopted for the interstate highway system. Access to all interstates was to be fully controlled. There would be no intersections or traffic signals. All traffic and railroad crossings would be grade separated, requiring the construction of more than 55,000 bridges. Interstates were to be divided and have at least four wide traffic lanes (two in each direction) and adequate shoulders. Curves were to be engineered for safe negotiation at high speed, while grades were to be moderated, eliminating blind hills. Rest areas were to be conveniently spaced. Each interstate was to be designed to handle traffic loads expected 20 years after completion.

The states were soon underway with construction. As time passed, it became clear that the goal of system completion by 1975 would not be achieved. But by 1960, more than 10,000 miles were opened. By 1965, 20,000 miles were opened, and by 1970, 30,000 miles were open to traffic. And by 1980, 40,000 miles were complete. While some segments remain to be completed, more than 42,700 miles of interstate highways are now opened to traffic. The interstate highway system serves virtually all of the nation's large urban areas and serves 49 states (all but Alaska). Despite this broad expanse, the interstate highway system represents just over one percent of the nation's road network.

NOTE: Much of the information in this section ("Background") is from Richard F. Weingroff, "A Partnership that Makes a Difference," Public Roads (Washington DC: United States Department of Transportation, Federal Highway Administration, Summer 1996) and "Development of the Interstate Program," in America's Highways: 1776-1976 (Washington, DC: United States Department of Transportation, Federal Highway Administration, 1976).

NOTE: There have been additions to the system beyond the 42,500 authorization.

NOTE: Some highways in Alaska have been eligible for receipt of federal interstate funding, but Alaska contains no highways that are formally designated as a part of the interstate standard system.).

Performance of the Interstate Highway System

There have been tremendous changes in America since authorization of the interstate highway system in 1956. Population has increased by 70 percent, but employment has increased by more than 100 percent. The percentage of the nation's population that is employed has increased by nearly one-third in 40 years, reflecting a far higher rate of female participation in the work force. Household size has declined significantly. These factors combined to increase travel demand at a far greater rate than had been expected. And much of this increased travel has been on the interstate highway system.

The interstate highway system is the "work horse" of the nation's highway system. Representing just over one percent of the nation's highway system mileage, the interstate highway system carries nearly one quarter (23 percent) of all roadway traffic, --- more than 20 times its one percent share measured in mileage (1), and more than 60 times as many person miles as all passenger rail services (Amtrak and urban rail) (2).

NOTE: Unless otherwise noted, "highway system" refers to the system of all urban roadways in the United States (urban, intercity, and rural).

NOTE: A person mile is one person traveling a mile. For example, a car with a driver and no passengers produces one person mile per each vehicle mile traveled. A car with a driver and two passengers produces three person miles for each vehicle mile traveled.

NOTE 1: Calculated from data in 1994 Highway Statistics (Washington, DC: United States Department of Transportation, Federal Highway Administration, 1995).

NOTE 2: Calculated from data in National Transportation Statistics 1996 (Washington, DC: United States Department of Transportation, Bureau of Transportation Statistics, 1996), 1994 Highway Statistics and National Transit Database 1994 (Washington, DC: United States Department of Transportation, Federal Transit Administration, 1996)..

Surface Transport Share: 1994

In Person Miles and Route Mileage Transport System Market Share Mileage Share Interstate 23.0% 1.1% All Other Roads 76.4% 98.2% Passenger Rail 0.6% 0.7%

The interstate highway system has a much higher density of use than other components of the nation's surface transportation system. The interstate highway system carries nearly 60,000 daily person miles per route mile, 26 times as many person miles per route mile as all other roads (including low usage rural roads), and 22 times as many person miles per route mile as intercity rail (Amtrak) and urban rail combined.

Each year, nearly one trillion person miles are carried on the interstate highway system --- a figure equal to providing trips around the world for 37 million people --- more people than live in Pennsylvania, Illinois, and Ohio combined. In its 40 years, more than 17 trillion person miles have been traveled over the interstate highway system.

NOTE: Assumes vehicle occupancy on the interstates equals that of the entire highway system. This is the equivalent of:

Nearly three trips around the world for each American.

A trip to the moon for all of the people living in California, New York, Texas, and New Jersey --- nearly 75 million people.

Three light years of travel through space --- nearly three-quarters of the distance to the nearest star outside the solar system (Alpha Centauri).

The interstates highway system in intercity and rural travel: The value of the interstate highway system may be most obvious in rural and intercity travel. For the most part, rural and intercity interstate travel is uncongested, permitting highly efficient traffic movement. Rural and intercity interstates provide a large measure of mobility, representing nearly 24 percent of all surface rural and intercity transportation --- 60 times that of passenger rail (Amtrak).

NOTE: Calculated from data in National Transportation Statistics 1996 (Washington, DC: United States Department of Transportation, Bureau of Transportation Statistics, 1996) and 1994 Highway Statistics.

Intercity & Rural Market Share: 1994

In Person Miles Interstate 23.7% Other Highway 75.9% Passenger Rail 0.4%

Rural and intercity interstates also play a crucial role in freight transportation. It has been estimated that 45 percent of the nation's large truck (tractor-trailer) operations are on the interstate highway system.

NOTE: Benefits of Interstate Highways (Washington, DC: United States Department of Transportation, Federal Highway Administration, 1983).

Interstate highways have generally reduced travel times by 20 percent or more between cities. For example:

NOTE: Travel time comparisons from analysis of "United States Mileage Chart" and "Driving Distances and Driving Times" in American Automobile Association maps of the United States (Heathrow, FL: American Automobile Association: 1954, 1955 and 1996).

Travel time between Seattle and Portland, Oregon has declined by nearly 25 percent.

Travel time between Cleveland and New York City has declined by a third.

Travel time between Atlanta and Birmingham has declined by nearly 40 percent.

Travel time between Chicago and Minneapolis has declined by nearly 25 percent.

The time advantage of the interstates remains clear even today, when interstate and non-interstate corridors are compared.

The average speed from Harrisburg to Albany, which is served by interstates, is more than 20 percent greater than from Harrisburg to Buffalo, which is not served by an interstate highway. NOTE: Travel time comparisons from analysis of "Highway and Driving Times Map," Rand McNally 1996 Road Atlas (Skokie, IL: Rand McNally Company, 1996).

Travel time from Sacramento to Salt Lake City, served by an interstate, is 1.5 hours less than virtually the same distance from Phoenix to Salt Lake City, which includes a major gap without an interstate.

Average travel time from Springfield, Missouri to Alexandria, Louisiana, which is not served by an interstate, is more than 40 percent longer than Springfield to Dallas, which is served by an interstate.

The interstate highway system in urban travel: The positive role of the interstates in the nation's urban areas is often overlooked or even discounted. In the early stages of interstate planning (1940s and early 1950s), proposed programs omitted cities from the system, limiting the role of the interstates to intercity transportation. The urban interstates were added to the system at the insistence of urban interests.

The interstate highway system provides crucial mobility in urban areas. The interstate highways provide a backbone transportation system that expedites urban trips for automobiles, buses, and trucks, while reducing traffic congestion on non-interstate arterials.

Even in New York City, which relies on non-highway (urban rail) transportation to a far greater extent than any other U.S. metropolitan area, the interstate highway market share (measured in person trips) is nearly double that of the region's sprawling rail system. In other urban areas, the interstate highway system is even more important, with interstate market share exceeding that of rail transit by more than thirty times.

NOTE: Estimated from data in 1995 Highway Statistics and National Transit Database 1994. Average urban interstate vehicle occupancy is estimated at 1.65, based upon analysis of data in the 1990 National Personal Transportation Survey and 1994 Highway Statistics.

Among the 30 largest urbanized areas outside New York City, interstate highways carry from seven to 10 times the person miles of non-highway modes (primarily urban rail) in three urban areas (Boston, Chicago and Philadelphia); from 10 to 50 times as many person miles in four (San Francisco-San Jose, Washington-Baltimore, Atlanta and Miami-Fort Lauderdale); and from 50 to 150 times in eight urban areas (Buffalo, Cleveland, Pittsburgh, Portland St. Louis, San Diego, New Orleans and Sacramento). In the remaining urban areas, non-highway market share is negligible in comparison with that of the urban interstate highways (Table A-1).

NOTE: Estimated from data in 1994 Highway Statistics and National Transit Database 1994.

Urban Market Share: 1994

In Person Miles Other

Urban Areas New York City

Urban Area Interstate 21.7% 13.6% Other Highway 77.6% 78.7% Rail Transit 0.7% 7.7%

Each lane of urban interstate is capable of moving between 2,500 and 4,000 persons per hour. This huge volume of traffic qualifies interstates as among the most effective urban mass transportation systems. The average urban interstate lane carries more people on a daily basis than the most successful of the nation's new light rail systems (1), and many interstate lanes carry more people than rail lines during their peak travel hours (2).

NOTE 1: The average interstate lane carries 12,888 vehicles daily (1994 Highway Statistics) and an estimated 42,500 people (estimated using average vehicle occupancy rates). New light rail systems with the highest daily ridership are Los Angeles (nearly 40,000), Buffalo, Portland and St. Louis (each between 25,000 and 30,000) (National Transit Database 1994).

NOTE 2: Based upon peak hour light rail ridership data as reported in Dennis L. Christiansen, High Occupancy Vehicle System Development in the United States (Washington, DC: United States Department of Transportation, 1990).

Interstates are capable of carrying far more people where they include high-occupancy vehicle lanes that expedite trips for buses and car pools. The most successful high occupancy vehicle lane carries up to seven times the volume of general purpose lanes, and more people during peak hour than any of the nation's urban rail lines outside New York City. Interstate high occupancy vehicle lanes provide a form of mass transportation that cannot be provided by conventional mass transit services, providing commuters with door-to-door convenience, and faster and more efficient access to the entire metropolitan region, not just the downtown markets to which efficient mass transit services are necessarily limited. This vastly increases potential destinations in the mass transportation market beyond the downtown areas, which comprise, on average, only one-tenth to one-thirtieth of employment in urban areas.

Urban residents use the interstates primarily because of the time that they save. In urban corridors, time savings of up to 60 percent have been observed.

NOTE: Benefits of Interstate Highways, 1970.

And while traffic congestion is increasing, the urban interstate highway system has continued to perform effectively, despite the fact that the 20 year capacity growth for which they were designed has long since passed in most cases. As employment and residences have spread, and as the number of work trips has increased, work trip travel times have declined, and average work trip distances have increased.

NOTE: Calculated from data in Nationwide Personal Transportation Survey (Washington, DC: United States Department of Transportation, Federal Highway Administration, 1977 and 1990).

NOTE: Calculated from data in Nationwide Personal Transportation Survey: Urban Travel Patterns (Washington, DC: United States Department of Transportation, Federal Highway Administration, 1994).

The urban interstates are the high capacity component of what has developed as the world's most democratic, extensive, highly used, inexpensive, and flexible system of urban mass transportation --- the urban highway system.

Cost of the Interstate Highway System

In 1958, the United States Department of Commerce estimated that the interstate highway system would cost $41 billion to construct. Through the years, Congress required periodic reports from the Federal Highway Administration on system progress and the cost to complete the system. In the forty years that have passed, legal, regulatory and political changes have greatly expanded the scope of the interstate highway system. Through 1989, total interstate costs were 37 percent above the original estimate. Most of the difference between the original estimate and the actual cost is attributable to elements that were not anticipated in the original estimate, such as unit cost inflation (more than half of the increase, or 13.8 percent of total costs), and system revisions, such as system additions, and new environmental, safety, relocation and other requirements (40 percent of the increase, or 10.7 percent of total costs). Other cost increases --- the extent by which the original estimate underestimated the cost of the system as anticipated at the time --- accounted for less 10 percent of the increased costs (2.2 percent of total costs). It is estimated that the total construction cost of the interstate highway system, through 1995, is $329 billion in 1996 dollars ($58.5 billion in 1957 dollars).

NOTE: The last analysis of interstate cost changes was completed by the Federal Highway Administration in 1991 and covered expenditures through 1989.

NOTE: Methodology: Classification of diversion from original projection estimated based upon an analysis of data in Interstate Cost Estimate reports from 1958 through 1991 (produced by the United States Department of Commerce and the United States Department of Transportation). Total construction cost estimated using annual federally funded construction costs (including preliminary engineering, right of way acquisition and construction) supplied by the Federal Highway Administration (unpublished), adding a factor to account for non-local costs (based upon the ratio of costs from 1957 to 1990 in the 1991 Interstate Cost Estimate. Inflation adjustment based upon gross domestic product implicit price deflator.