Interstate highways are a network of roads in the United States designed for long-distance travel and efficient transportation. Established by the Federal-Aid Highway Act of 1956, these highways connect major cities and regions, facilitating commerce and travel across state lines. They are typically wider than regular roads and have limited access points to ensure smooth traffic flow. The interstate system is numbered, with odd numbers indicating north-south routes and even numbers for east-west routes. These highways are crucial for emergency response, military movement, and economic activities, making them an essential part of the U.S. transportation infrastructure.