List of suffixed Interstate Highways

Dwight D. Eisenhower National System of Interstate and Defense Highways
Highway shields for Interstate 35E and Interstate 69W
The 1958 Interstate Highway System plan included many suffixed Interstates.
System information
Formed	June 29, 1956[1]
Highway names
Interstates	Interstate X (I-X)
System links
Interstate Highway System Main Auxiliary Suffixed Business Future

In the United States, there are currently seven routes in the Interstate Highway System that are signed with letter suffixes to the route number. Interstate 35 (I-35) splits into I-35E and I-35W in the Dallas–Fort Worth metroplex in Texas, and similarly splits into I-35E and I-35W in the Minneapolis–St. Paul area in Minnesota. Other suffixed Interstates include I-69C, I-69E and I-69W in South Texas, and I-480N in Ohio, which is designated as such on mile markers but is otherwise unsigned. The state of Maryland has several unsigned suffixed Interstate designations that are designated by the Maryland State Highway Administration, rather than by the Federal Highway Administration (FHWA).

There were once many more suffixed Interstates, as the three-digit Interstates were not designated until after all major routes were assigned numbers. Most of these were spurs; the suffixed route did not return to its parent. In 1980, the American Association of State Highway and Transportation Officials (AASHTO) abolished the majority of suffixes due to confusion, renumbering them as three-digit Interstates. For example, I-15E in California has since become I-215.