Simplify the following text for a Grade 8 native English-speaking person.
Original: The Dwight D. Eisenhower National System of Interstate and Defense Highways , commonly called the Interstate Highway System or Interstate Freeway System , and colloquially abbreviated `` the Interstate '' , is a network of limited-access roadways ( also called freeways or expressways ) in the United States . It is named for President Dwight D. Eisenhower , who championed its formation .
Simplified: The Dwight D. Eisenhower National System of Interstate and Defense Highways ( often called the Interstate Highway System , Interstate or I - ) , is a group of roads in the United States .