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The Interstate Highway System, or simply interstates, refers to the highways connecting different states and cities across the United States. Interstate highways are often the quickest way to get from one state to another by land. Compared to conventional roads, most interstates are generally straighter and wider. Additionally, they typically don’t have any stop light intersections to prevent congestion. These factors contribute to interstates being the quickest way to get from one place to another, even within the same state.

Which States have the Most Miles of Interstate Highway?

The following states have the most miles of interstate highways:

  • Texas – 3,233 miles
  • California – 2,456 miles
  • Illinois – 2,169 miles
  • Pennsylvania – 1,759 miles
  • Ohio – 1,572 miles
austin interstate highway
Texas has the most miles of interstate highway with 3,233 miles.

There could be several reasons why these states have the most interstate mileage. One of these reasons is size. Texas and California are the two largest states in terms of area (excluding Alaska). To understand why there are so many miles of interstate, we have to understand why the interstate highway system was implemented in the first place.

History of Interstate Highways

In 1919, a convoy of vehicles made a trip from Washington DC to California to make a report about America’s roads at the time. They took 62 days to complete the trip, and they wrote back that trips like that were simply impractical. As America developed, states were able to build better rural and urban roads. However, many states particularly in the south and west were still unable to build roads for inter-state travel. Additionally, the main form of inter-state travel and transport at the time was by rail.

However, this changed when the Americans were able to observe Germany’s autobahn system during World War 2 and how it made commerce and industry incredibly efficient.

The Federal-Aid Highway Act was originally enacted in 1944, which called for a national system of interstate highways. However, funding for the project was only straightened out when President Eisenhower enacted the Federal-Aid Highway Act of 1956. His initiatives made the project possible by making the Federal Government pay for 90% of the project, which was largely funded by a hike in the federal gas tax.

The law also laid down design standards for interstates to keep them safe and free from traffic. These standards included the use of on and off-ramps instead of stop lights and intersections and speed limits of 50 to 70 miles per hour, depending on whether an area is urban or rural. The guidelines also stated that interstates should have a minimum of two lanes in each direction and that each lane should be 12 feet wide, with a 10-foot paved shoulder on the right and a 4-foot paved shoulder on the left.

This project was completed in 1992, 36 years after it began. Thanks to the interstate system, driving from Washington D.C. to California would “only” take 42 hours. Interstates also connect the US’ economic centers to peripheral areas. These allowed distant, rural communities to have easier access to cities and ports.

A transportation network makes markets more competitive, and an efficient transportation system improves the allocation process because it widens the number of opportunities for both suppliers and buyers. Despite accounting for only 2.5 percent of US roadway lane miles, interstates carry 25% of all traffic and more than 50% of truck traffic, moving almost $14 trillion in commodities and products each year.

birds eyeview of los angeles interstate
Routes with odd numbers travel north and south, while routes with even numbers run east and west.

How Interstate Highways Are Named

The American Association of State Highway and Transportation Officials developed a naming system for highways to more easily identify and differentiate them. Interstate highways are named using one- or two-digit numbers. Routes with odd numbers travel north and south, while routes with even numbers run east and west. The lowest-numbered north-south routes begin in the west, whereas the lowest-numbered east-west routes begin in the south.

There are also cases where an interstate diverges into branches. In these cases, each branch is named just like the main route, but it’s followed by a letter signifying a direction of travel (east, west, etc).

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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