Exit numbers in the United States

The Manual on Uniform Traffic Control Devices (MUTCD) encouraged use of mileposts and exit numbering by 1961.

However, the 2006 edition of the California Manual on Uniform Traffic Control Devices removed any sort of compliance deadline for the exit numbers.

Although a ten-year compliance period was proposed for the new edition of the MUTCD,[2] 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.

The mile-based requirement mandates multiple exits in the same mile to use a letter suffix in alphabetical order.

Older exit numbering schemes sometimes use cardinal directions (E, N, S, W, often E-W or N-S) depending on the directionality of the cross route(s), for example I-93 in New Hampshire uses exits 15E and 15W for the cloverleaf interchange with US 202 in Concord which is signed east and west at the interchange.

I-19 currently has all exit numbers and distances in kilometers, but speed limits in miles per hour.

For example, North Carolina uses mileage-based exit numbers on all of its freeways, including interstates.

Exit Numbers in the United States by State as of August 2021[update]
Exit Numbers in the United States by State as of August 2021
An example of a green exit number plaque for two exits at the same interchange
An example of a green exit number plaque for a left exit with a yellow "left" panel
Old mile tabs on I-295 in Rhode Island , several other states did this. As of September 2007 , these signs have been replaced and use only the sequential exit number scheme. Exit numbers on I-295 have since been converted to mile-based numbers.
An example of sequentially-numbered exits in Connecticut on the Charter Oak Bridge , Route 15 / US 5 ; the state has begun the federally mandated conversion to mile-based exits.
Mile-based exit numbers on I-4 in Volusia County, Florida, circa 2003. In this case, mile-based exits 111A and 111B had been sequential exits 53CA and 53CB, as the tab shows. The extra tabs have been removed and the signs now solely use the mileage based exits.