Transportation Deployment Casebook/Life Cycle of the Interstate Highway System
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Mode & Markets 
The Interstate Highway System, formally known as the "Dwight D. Eisenhower Interstate Highway System," is a network of cross-country automobile highways, devoid of traffic lights, with grade separated crossings and limited access. The main advantage of this design is not having to stop for cross traffic. By not having to stop at traffic lights or stop signs, momentum is not lost, and energy for travel is used more efficiently. The main markets for the Interstate Highway System include: the military, freight travel by heavy trucks, and of course the automobile. The interstate Highway System is also referred to as the "freeway."
Setting the Scene 
Prior to the advent of the Interstate Highway System, automobiles had already become the most popular and, in some cases, preferred mode of travel in urban centers, especially new suburbs. However, most interstate travel, including the shipping of goods, was done via the railroads. Although the railroads were and still are a more efficient way of moving mass amounts of goods, the rigid track system with it's mainly set courses made it difficult to provide last-minute shipments. The freedom of mobility, and the unlimited routing possibilities an interstate highway system could provide, was what initially stirred interest in such a project. But it was National Defense concerns and military interests that were used to justify to the public the necessity of funding the project; and in 1956, the Federal Aid Highway Act was passed.
The Interstate Highway System's design was heavily influenced by the "Autobahn" highway system in Germany. During World War II, General Dwight D. Eisenhower saw the advantage Germany had over American Allies at moving troops and ammunitions around Germany. However, this is not to say the United States didn't already have examples of highways with grade separated crossings, they did, but on a much smaller scale. The Pennsylvania Turnpike, which later was incorporated into the Interstate Highway System, is one example of this. There were many limited access interstate highways prior to the implementation of the Interstate Highway System, however, these were usually winding, narrow roads with few lanes and at-grade crossings.
The greatest difference between the U.S. Interstate Highway System and Germany's Autobahn is where each highway system runs in relation to the respective country's urban centers. The Interstate Highway was initially designed to go around urban areas, like the Autobahn does. However, in it's implementation, the Interstate Highway System ended up cutting through urban centers. This design alteration was intentional, in the hopes that it would generate economic development in urban centers. The design change had both intentional and unintentional consequences. The design intentionally cut through low income neighborhoods, displacing many. However, some unintentional consequence include: the creation of new barriers which broke up the urban fabric, enabling decentralisation and sprawl on a level never before seen, and, consequentially, the decline of urban centers.
The shift from rural highways to the Interstate Highway System--for Interstate travel--came naturally, and was seen by most as a great improvement over the previous highway system. Some new design elements, which the public had to adapt to, include: on-and-off ramps, signage, higher posted speed limits (which speeds people were happy to go), and interchanges. Regardless of these new infrastructural additions, the rules of the road, such as passing on the left or signaling to change lanes, stayed the same.
The Role of Policy 
During the birthing stage, and well into the growth phase, individual states set their own speed limits. They ranged from 40 miles per hour to 80 miles per hour. It wasn't until 1974, when President Nixon signed the Emergency Highway Energy Conservation Act, that a national speed limit of 55 miles per hour was locked in and enforced, in the hopes it would lower foreign oil dependence. 55 miles per hour was supposedly the most fuel efficient speed for automobiles of that day. This Act wasn't repealed until 1995. Today speed limits range anywhere from 35 miles per hour to 80 miles per hour, depending on the terrain and the amount of access points.
Growth and Implementation 
The Federal Highway Act of 1956 sent the Interstate Highway System into a major growth phase. 90% of the original funding came from a government sanctioned one cent gas tax. the rest of the funding came from the individual States, who all got their funding by similar means. All funding came from the public sector. The only role the private sector might have played in the implementation of the Interstate Highway System was influencing the location of acces points on the freeway.
In urban centers, limited access points on the Interstate Highway System were not as limited as in rural areas. As a result, people began using the freeway for short trips around town and as a way to commuting to work. with higher speed limits, people could travel farther distances in less time. Therefore, houses out in the suburbs, which prior to the Interstate were impractical, now seemed practical. Many people moved to suburbs with convenient access to the Interstate. However, because so many people decided to move out to the suburbs and become dependent on this one system of transportation, the system became strained in urban areas resulting in stop and go traffic jams. In an attempt to relieve this congestion, many of the urban freeways have been widened. But these efforts proved to be in vain, as tripple convergence would undoubtably occur.
The Interstate Highway system reached maturity in the early 1980's, and today the infrastructure is mostly built out. Durring the maturity phase, there were many attempts to make the system more efficient; new policies and infrastructure were tried, tested, and implemented. Examples of these include: Traffic System Management Tools such as ramp meters; Highway Helpers; HO/T (HOV) Lanes; Park and Ride Lots (to encourage the use of an alternate mode); Highway Access Management; and Peak Pricing. Beyond these, there isn't much that can be done to improve the Interstate Highway infrastructure. Future advancements, if any, will likely be due to improvements made to the vehicles that use the road. There have been great advancements in automated vehicles. These advancements, if fully realized, may be the answer to the inefficiencies of the current system.
The Typical "S Curve" 
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