Exit numbers in the United States


In the United States, exit numbers are assigned to freeway junctions, and are usually numbered as exits from freeways. Exit numbers generally are found above the destinations of the exit, as well as a sign in the gore. Exit numbers typically reset at political borders such as state lines. Some major streets also use exit numbers. Freeway exits in the United States are usually numbered in two formats: distance-based and sequential.

Interstate Highways

The Federal Highway Administration generally requires exit numbers on the Interstate Highway System; the FHWA established that requirement in 1970. The Manual of Uniform Traffic Control Devices encouraged use of mileposts and exit numbering by 1961. The MUTCD mandated exit numbering in 1971. The FHWA granted California an exception due to the cost of installing and maintaining additional signage. California was able to obtain a waiver because it had already built most of its freeways, although some freeways in Los Angeles County received junction numbers: Interstate 10 was the only freeway in the county that had a complete set of junction numbers. Interstate 5, US 101, and then CA 11 were numbered for short distances from downtown Los Angeles. Freeway connections were unnumbered, and junction numbers were only shown on plates, not on gore signs. In 2002, the Cal-NExUS program began to completely number California's junctions. The program is not well-funded, especially because of California's budget woes, so exits are only being signed with numbers when signs need to be replaced. As the efficiency of an exit numbering system for navigational purposes depends on all exits being consistently numbered, the usefulness of the system while only some exits are numbered is limited. Originally, the initial completion date for this project was set as November 2004. The deadline was then extended to 2008. However, the 2006 edition of the California MUTCD removed any sort of compliance deadline for the exit numbers.
Nine states, mostly in the Northeast, and the District of Columbia use sequential numbering schemes on at least one highway, although the 2009 edition of the Manual on Uniform Traffic Control Devices requires these jurisdictions to transition to distance-based numbering. Although a ten-year compliance period was proposed for the new edition of the MUTCD, a compliance date for this change was ultimately not adopted with the 2009 edition, meaning that the transition is accomplished through a systematic upgrading of existing signing and there is no specific date by which the change must be implemented. However, the FHWA has required that all federally funded routes with sequential numbering eventually be converted to mileage-based exit numbers. To that end, the FHWA has required each state that currently uses sequential exit numbering to submit a plan to eventually transition to distance-based exit numbers. Some of the states that currently have sequential numbering either have or intend to request a waiver from the Federal Highway Administration to retain their current numbering systems, while others have planned a gradual transition to mileage-based exit numbering over time as existing signage reaches the end of its serviceable life and is replaced.
The mile-based requirement mandates multiple exits in the same mile to use A, B, C, etc. This also applies to divided interchanges, where two exits are used for opposite directions of the road, for example on full cloverleaf interchanges. Older exit numbering schemes sometimes use cardinal directions depending on the directionality of the cross route, for example Interstate 93 in New Hampshire uses exits 15E and 15W for the cloverleaf interchange with U.S. Route 202 in Concord which is signed "east" and "west" at the interchange. Many exits in the Northeastern states which currently or formerly used sequential numbering schemes had these directional abbreviations, but most have converted to A-B schemes.
Several exits on the New Jersey Turnpike use E and W suffixes on the portion where the roadways split ; one interchange on the eastern spur is numbered 15X, as there already was a 15E.
, CT 15/U.S. 5.
Several states still maintain systems other than the MUTCD-standard mileage based systems, among these are:
Connecticut planned to convert I-91 to mileage-based exit numbering in 1974; however, CONNDOT abandoned that initiative due to objections from local businesses.
Two highways have metric numbering, because they were constructed during the time when the U.S. was thought to be completely converting to metric. Delaware Route 1 has used standard mileposts since 2003 when the metric-based posts were replaced, and several exit numbers do not coincide with either the milemarker nor its kilometer conversion as they are offset by miles from a kilometer-based exit. I-19 currently has all exit numbers and distances in kilometers, but speed limits in miles per hour. The road has received funding for the distances to be changed back to miles, but in response to local opposition against exit number changes, the Arizona Department of Transportation had decided to spend the money on other roads instead.

Other highways

Exit numbering on non-Interstate highways is less consistent. For example, Texas, which normally uses mile-based exit numbering, uses sequential numbering on U.S. Route 75 between downtown Dallas and the Oklahoma border. Similarly, the U.S. Route 54 freeway from El Paso to the New Mexico border also uses sequential exit numbering.
Many states formerly used sequential numbers, and in some cases used exit numbers sparingly, if at all. The following states have introduced mile-based exit numbering on some or all of their highways: