The interstate highway system was one of the important factors that supported the trends of increased automobile use and the suburbanization of population and jobs. The length of the Dwight D. Eisenhower National System of Interstate and Defense Highways is 47,856 miles (77,017 km). The National Highway System covers 160,000-mile (260,000 km).

Why was the Interstate Highway System built? The Interstate Highway System was built to enable traffic to move quickly and efficiently across the nation and goods to be distributed  more efficiently. The new highways allowed people living in the suburbs to commute to jobs that were miles away

When was the Interstate Highway System built? President Eisenhower signed the National Interstate and Defense Highway Act on June 26, 1956 beginning the construction Interstate Highway System and the building of freeways continues to this day

What U.S. state capitals are still not served by the Interstate Highway System? The The 4 state capitals are still not served by the Interstate Highway System are Juneau (Alaska), Dover (Delaware) Jefferson City (Missouri) and Pierre (South Dakota)

Facts about Interstate Highway System
The following fact sheet contains interesting facts and information on Interstate Highway System.

The Dwight D. Eisenhower National System of Interstate and Defense Highways is a network of controlled-access highways that forms a part of the United States National Highway System. A controlled-access highway provides an unhindered flow of traffic.

The "free-flowing" system had no traffic signals, intersections or property access. The controlled entrance and exit points allowed cars to travel at much faster speeds

The construction of the interstates began during the presidency of Dwight Eisenhower. He was inspired to start there project by his experiences in traveling long distances.

In 1919 Eisenhower joined nearly 300 members of the army to travel 2,800 miles across the country from Washington D.C. to San Francisco. The journey took 62 days and averaged just 5 miles per hour. At this time in history the roads were made not of asphalt or concrete but were old trails consisting of packed dirt or mud. In the 1920s, 70% of travel between cities was by railroads

The first petrol or gasoline powered automobile was only invented in 1886 by Karl Benz. In 1903 Henry Ford opened the Ford Motor Company and by 1908 the Henry Ford Model T automobiles were coming off the production line. Americans had cheap access to automobiles which were great in the cities but restricted outside due to the lack of roads.

The nation needed new roads and before 1956 the federal government split the cost of road building with the states.

Eisenhower's career in the army took him to Europe during WW2 and he was greatly impressed with the Autobahn, Germany's freeway system that provided transport routes for military supplies and troop deployments.

Ike assumed the presidency in 1953 in the early stages of the Cold War with USSR. Tensions were high and the ability to move troops and equipment quickly and efficiently across the country gained vital importance as an efficient infrastructure could well determine whether America could survive a Soviet attack.

The disorganized infrastructure of the country had 2-lane highways but these were not connected in a rational and efficient manner.

In addition the number of Americans with cars was increasing rapidly. In 1950 there with 25 million registered automobiles on the road and the need for efficient new routes for travel also increased. (By 1958, this figure would increase to more than 67 million cars)

President Dwight D. Eisenhower signed the National Interstate and Defense Highway Act on June 26, 1956 that authorized the construction of a 41,000-mile network of interstate highways that would span the nation and allocated $26 billion to pay for them.

The passage of the law began the construction of the Interstate Highway System. Road signs were standardized. Exit signs had white writing on a green background and interstate route signs were red, white, and blue. The signs for rest areas were white on blue.

The National Interstate and Defense Highways Act. The reason the word "Defense" was added to the title of the Act was firstly because some of the original cost of the project was diverted from defense funds. Secondly, most US Air Force bases would have a direct link to the system.

The Yellow Book officially known as the General Location of National System of Interstate Highways, mapped out what became the Interstate System. Charles Erwin Wilson, who was still head of General Motors when President Eisenhower selected him as Secretary of Defense in January 1953, assisted in the planning.

The Interstate Highways were planned so that they connected to other roads that were a part of the Strategic Highway Network, and identified as critical to the United States Department of Defense.

The interstates had overpasses and underpasses instead of intersections. They were at least 4 lanes wide and were designed for high-speed travel.

The money to pay for the ambitious project came from the Highway Trust Fund that paid for 90% of highway construction costs with an increased gasoline tax, with the states required to pay the remaining 10% of the cost. Interstate highways are owned by the state in which they were built.

The initial cost  of the project estimate of $25 billion over 12 years ended up costing $114 billion and took 35 years. Approximately 2,900 miles (4,700 km) of toll roads are included in the Interstate Highway System.

Advantages: The interstates enabled a faster and more efficient distribution of goods aiding the US economy. Goods could be shipped longer distances, expanding market area for farms, and manufacturing companies moved to cheaper locations, reducing costs and increasing profits. The interstates also contributed to the growth of suburban communities allowing people to commute to jobs that were miles away from their homes.

Advantages: The interstates drastically reduced the amount of time to cross the continent of North America. Ike's original trip took 16 days (it now takes just over 4 days). The fatality rate on interstate highways was lower than on other roads and over 50 years, the Road Information Project estimates that the interstates have saved about 234,000 lives

Disadvantages: The construction of the interstates disrupted the lives of many Americans, and destroyed the wildlife in their paths. The highways ruined the city neighborhoods in their path. People lost their homes and their friends and neighbors as established communities were sliced in half.

Disadvantages: The interstates led to abandonment and decay in towns and cities. Americans, who had initially supported the system began to fight against it. The opposition mounted by many anti-road activists and campaigners prevented interstates running through their areas and ruining their neighborhoods and as a result, many urban interstates ended abruptly and were called the "roads to nowhere."

The numbering system for the Interstate Highway System was developed in 1957 by the American Association of State Highway and Transportation Officials (AASHTO). The numbering system for the assigned even numbers for the east-west highways and odd numbers for the north-south highways

The interstates system allows the procedure known as the 'contraflow lane reversal' to be put into place. This procedure maximizes traffic throughput on a highway by reversing the flow of traffic on one side of a divider so that all lanes become outbound lanes. The 'contraflow lane reversal' procedure facilitates evacuations during times of natural disasters such as hurricanes.