Exit Numbers in The United States - Interstate Highways

Interstate Highways

The Federal Highway Administration (FHWA) generally requires exit numbers (mile-based or consecutively) on the Interstate Highway System; the FHWA established that requirement in 1970. The Manual of Uniform Traffic Control Devices (MUTCD) 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 (now I-110/CA 110) 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.

Eleven U.S. states as of June 2008 use sequential numbering schemes, although the 2009 edition of the Manual on Uniform Traffic Control Devices (MUTCD) requires these states to transition to distance-based numbering. Although a ten-year compliance date 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.

• Alaska - only on the Johansen Expressway in Fairbanks. Mile-based.
• Connecticut - All sequential. Several non-Interstate freeways have interchanges without exit numbers. Connecticut planned to convert I-91 to mileage-based exit numbering in 1974, but CONNDOT abandoned that initiative due to objections from local businesses.
• Delaware - On I-95, I-495, and Delaware Route 141 only. Delaware Route 1 uses kilometer-based exit numbers (despite using milemarkers), and I-295 has no exit numbers at all.
• District of Columbia - Historically, the only exit numbers posted in the District consisted of sequential numbers on Interstate 295. The few other freeways within the District of Columbia did not have exit numbers, but in 2008 the District began posting sequential numbers on Interstate 395. As of June 2008, not all interchanges had received numbers. The close proximity of the interchanges on this short freeway, coupled with the lack of space for new interchanges, renders the sequential system more practical than the mileage-based.
• Massachusetts - All sequential (experimented with dual exit/mile tabs in the 1970s).
• Maryland - The Baltimore Beltway is sequentially numbered.
• New Hampshire - All sequential.
• New Jersey - Sequential numbering on the New Jersey Turnpike, Palisades Interstate Parkway, and I-676; all other New Jersey exit numbering is mile-based. (The Brigantine Connector in Atlantic City uses letters for exits.) Many New Jersey freeways lack exit numbers.
• New York - Sequential, except I-890 in Schenectady. and I-95 in New York City south of the Pelham Parkway.
• Rhode Island - All sequential; experimented with dual exit/mile tabs in the 1970s.
• Vermont - Route 289 (Circumferential Highway) has mileage-based exit numbering.

Most other states began with sequential numbers and switched over later. Here is a list of these switches, in the order that they happened:

• Colorado - Used dual mile/junction plates into the mid 1970s; initially used sequential numbering.
• Indiana - Around 1980.
• Iowa - May have had sequential numbers on Interstate 80 in the early 1970s. Adopted distance-based exit numbering in 1977.
• Ohio - Between 1972 and 1974 (though the Ohio Turnpike continued to carry both systems until 2000).
• New Jersey - Around 1970. The New Jersey Turnpike kept sequential exit numbering.
• Mississippi - 1980s.
• North Dakota - 1980s
• Virginia - Early 1990s; exceptions include Route 267 (suburban Washington, D.C.) and Interstate 581 (Roanoke). I-581 utilizes sequential exit numbers; furthermore, Exit 1 is at I-581's northern end.
• Georgia - Began January 4, 2000, now complete. (Interstate highways only).
• Pennsylvania - Began April 2001 on Interstates and all highways of the Pennsylvania Turnpike system. Prior to renumbering, junctions solely between two-digit interstates were not numbered (for example, the junction of I-79 and I-80). Sequential numbering skipped these junctions.
• Florida - Began January 28, 2002, now complete. However, I-110 retained its sequential exit numbers.
• California - Began January 2002. California was the only state not to require exit numbers or mileposts, because most of their highway system was built prior to the federal requirement. Before adopting exit numbering, California relied on its system of county-based mileposts on all highways, without having explicitly numbered exits.
• Maine - Early 2004 (experimented with dual exit/mile tabs in the 1970s).
• New York - The state senate passed S.5358-A, sponsored by Tom Libous (R-C-I, Binghamton) on June 10, 2008. The bill directs the New York State Department of Transportation and the New York State Thruway Authority to convert the state's exit numbers from sequential to mileage-based by January 1, 2012. On April 23, 2008, the New York State Assembly began considering its own version (A10676) that was nearly identical to the bill passed in the Senate. The bill died in committee at the end of the 2008 legislative session.

Two highways (Interstate 19 in Arizona and Delaware Route 1) 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 currently uses standard milepost when the metric-based posts were replaced. 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.