Transportation Deployment Casebook/The Life Cycle of the Interstate Highway System

The Interstate Highway System is an interregional network of high-speed roads authorized under Dwight D. Eisenhower on June 29, 1956. The network connected metropolitan areas, landmarks, and industrial areas, as well as provided mobility for the national defense system. The Interstate Highway Network has provided efficient routes for shipping, travel, and defense. It has lead to decreases in travel time and freight costs. With this connectedness, the United States has become a leader in super-highways with over 47,000 miles of road.

S-Curve Modeling the Birth, Growth, and Maturity of the Interstate Highway System
The S-Curve is used to model the life cycle of transportation modes. It depicts the birth, growth, and maturity of the mode.

The Life Cycle of the Interstate Highway System
The S-Curve model depicted below shows the mileage of the Interstate Highway System. It begins at a point greater than zero, because paved interregional roads existed before 1956. With the Federal-Aid Highway Act of 1956, the Interstate designation was implemented. This designation was given to many existing roads. The existing interregional road mileage cannot be extracted from the road data in a meaningful way.

Methodology
The S-Curve model follows the formula S(t) = K/[1+exp(-b(t-t0)] where Using this method, the S-Curve was shown to be a good fit, with an R^2 of 0.91. The R^2 is an indicator of the goodness of fit for the regression used to estimate this curve.  K was estimated to be only slightly higher than the existing network, 48,500 miles, due to the slowing growth of roads and a shifted focus to maintenance by the Federal government.  T0, the point where mileage was 24,250, was determined to be 1922, following the growth patterns backward. Because the data begins after t0, only the top of the S curve is shown. Data was collected from the Highway Statistics publication provided by the Federal Highway Administration
 * K= point of saturation
 * b= a constant
 * t= year
 * t0= inflection point representing 1/2 K

World War I Era
Long distance freight in the early 20th century was relegated shipped via railroads. World War I increased demand of American goods in Europe. As railroads reached maximum capacity, merchandisers turned to semi freight to get their goods to port. As heavy loads were brought across America’s roads, they quickly deteriorated. With this deterioration, President Woodrow Wilson signed the Federal-Aid Highway Act of 1916. This increased federal funding for highways, provided money for rural post roads, and dedicated monies for roads through public lands.

The Great Depression and World War II
Franklin D. Roosevelt established a National Interregional Highway committee to explore a system of interregional highways. With the stock market collapse of 1929 and the unemployment that accompanied the Great Depression, the Federal-Aid Highway Act of 1916 was amended. From 1931 to 1933, $125 million was spent per year for road construction and improvements.

After the attack on Pearl Harbor, the United States entered World War II and the Federal Government's focus shifted to war strategy. In 1944, after the war, Roosevelt signed the Federal-Aid Highway Act of 1944 that authorized the designation of 40,000 miles of a connected interregional network, but no funding for construction of additional road mileage.

The Growth of the Automobile Throughout These Periods
With the moving assembly line and interchangeable parts, the personal auto became affordable for Americans and thus demand grew in the 1920s and 1930s. Suburbanization happened rapidly after World War II, and with poor public transit in the suburbs the demand for cars, and then roads, skyrocketed.

Eisenhower's Inspirations
In 1919, Dwight D. Eisenhower traveled in a convoy from Washington D.C. to San Francisco to demonstrate America’s “defense mobility.” The convoy traveled, on average, 58 miles per day (approximately 5 miles per hour), slowed by rough and muddy roads, accidents, and socializing. Eisenhower then experienced the superior roads of the German Autobahn during World War II; and witnessed the smooth flow of military soldiers and supplies. These two events impacted future policy Eisenhower would enact.

Policy's Role for Network Expansion
Without Federal Government policy, it is difficult to imagine what the extent of the Interstate Highway System would be. A series of federal research studies and legislative acts through the early 20th century lead to a massive overhaul of the road system, but arguably none more important than the Federal-Aid Highway Act of 1956. On June 29, 1956 Dwight D. Eisenhower signed the Federal-Aid Highway Act of 1956 into law. <ref name="40Years"/).  This bill authorized 41,000 miles of interstate highway to be completed by 1975.  This fund would be financed through an increase in the federal gas tax and other motor vehicle taxes. This legislation provided for 90% of costs associated with the construction of the new highways. It established nationwide standards for construction, regulating speeds and minimum travel lanes and width.  Other design aspects include fully controlled accesses, no traffic signals or intersections, and grade separated crossings.

Quality of Life
With increased travel speeds, it's logical to expect that travel time between locations would decrease. Travel times decreased by up to 40% between cities. Trips from Atlanta to Birmingham were 40% shorter after the interstate, while the travel time between Chicago and Minneapolis declined by 25%. More difficult to quantify are the benefits added with the increase in choice. American's now could choose larger spatial areas for housing, employment, health care, and retail. The timesavings afforded from the interstate highway system allowed people to spend more time doing what they want, and less traveling to and fro.

Safety
The construction of the Interstate Highway was highly regulated. It required engineering to that would allow speeds to be maintained and use of high quality materials As of 1996, the fatality rate for the interstate highways is nearly 60% lower than the rest of the system. The injury rate is estimated to be 70% lower. From 1957 to 1996, the safety related losses that were avoided by the use of the highway system were estimated to be $368 billion dollars (1996).

Economy
From 1950 to 1989, 25% of the nation's productivity increase is attributable to highways (the Interstate System plus all other urban and rural highways). The larger network provided more mobility of people and goods, expanding the market and competition. With the improved road network semi freight became competitive with railroads. Prior to the interstate system, the market for semi freight was primarily local deliveries. Freight costs decreased with the increase in road quality. With the decreased freight costs, semi freight was now competitive with rails. This lead to lower cost freight and increased reliability with deliveries.

Maturation of the Interstate System
The physical and economic landscape of America has permanently changed with the construction of the Interstate Highway System. The federal and state governments have shifted their focus from expansion to maintenance and from road expenditures to mass transit programs. Even further, some local governments, with the support of the federal government have begun to tear down certain elements to "correct" the social maladies that occurred during construction.

Problems with the System
The Highway Trust Fund is no longer funding highways exclusively. After 1973, these funds have been used to support light rail, mass transit, bus and bike lanes, among other alternative transportation modes. This may reflect the increased advocacy for a public transit system that more closely resembles international ones. In 1998 the Transportation Equity Act for the 21st Century added reconstruction to the authorized activities in the Interstate Maintenance Program. Previously the only federally funded activities were resurfacing, restoration, and rehabilitation. The interstate system solved many problems in the 20th century, but since falling into disrepair, has many problems it now needs solved. Most of the infrastructure has surpassed its life expectancy. In 1997, over five percent of bridges on the Interstate Highway System have been deemed structurally deficient. Congestion in major urban areas is a serious concern. It has been estimated that Americans spend 4.2 billion hours stuck in traffic, to the toll of $78.2billion. And it's only getting worse; the average daily vehicle miles traveled during congestion has grown from 25.9% in 1995 to 31.6% in 2004 with some regions exceeding that. The construction of the Interstate Highway System was highly contested. For many reasons, including environmental and racial and social inequality in the construction process, the highway was rarely popular in the neighborhoods it dissected. Many years later, cities have proposed the destruction of these interstates. The Park East Freeway in Milwaukee, Wisconsin was removed after Mayor John Norquist campaigned heavily for the removal and a return to the street grid. But Milwaukee is not alone in the desire to remove urban highways. New York, Boston, and others have already replaced their highway systems with tunnels or boulevards and cities like Nashville, Cleveland, Philadelphia, and St. Louis have discussed and planned the removal of their urban highways, with the support of the Federal Government.

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