List of suffixed Interstate Highways

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

Currently the Interstate Highway System includes seven suffixed routes that are signed: the Interstate 35 split into Interstate 35E and Interstate 35W at Dallas-Fort Worth, Texas; a similar split into Interstate 35E and Interstate 35W at Minneapolis-St. Paul, Minnesota; as well as Interstate 69C, Interstate 69E and Interstate 69W in South Texas; in addition, Interstate 480N in Ohio exists and is designated as such on mile markers but is otherwise unsigned. However, there were once many more, as the three-digit Interstates were not designated until after all major routes were assigned numbers, including some short connections and spurs. (A few of the shortest, including I-190 and I-195, were assigned three-digit numbers almost immediately.) Most were not equal splits like on I-35, but had the main route continue through, and often the suffixed route never returned to its parent. In 1980, AASHTO abolished the majority of suffixes due to confusion, renumbering them as three-digit Interstates, but several that return to their parents were kept. For example, Interstate 15E has since become Interstate 215, but both I-35E/I-35W and I-69 splits still exist.