Interstate Highway standards

Most of these were toll roads that were built before the Interstate system came into existence or were under construction at the time President Dwight D. Eisenhower signed the Federal-Aid Highway Act of 1956.

One example is the Pennsylvania Turnpike, which originally had a very narrow median that later required the installation of a steel guardrail and later a Jersey barrier due to heavy traffic loads.

[citation needed] The Kansas Turnpike had a 20-foot (6.1 m) depressed median (16 feet [4.9 m] narrower than the Interstate minimum) along its entire 236-mile (380 km) length from its opening in 1956 through the mid-1980s when Jersey barriers were installed.

[citation needed] Interstate 35E through Saint Paul, Minnesota is an example of a freeway that was not grandfathered into the system but is nonetheless an exception to standards.

All of the unsigned Interstates in Alaska and Puerto Rico are exempt from Interstate Highway standards and are instead, per Title 23, Chapter 1, Section 103 of the U.S. Code, "designed in accordance with such geometric and construction standards as are adequate for current and probable future traffic demands and the needs of the locality of the highway".