Exit numbers in the United States
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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 (and route number(s) ) 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.
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.
Nine states as of June 2008[update] 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 (MUTCD) 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 to adopt mileage-based exit numbers; 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 also mandates multiple exits in the same mile to use A, B, C, etc.; the "consecutive" numbering scheme (which must be phased out) for multi-directional interchanges sometimes uses N-S, or E-W.
- Connecticut – Sequential, except for I-395, Route 2A, and "secret" CT 695 which are mileage-based; these changes include the eastern end of the former Connecticut Turnpike. Several non-Interstate freeways have interchanges without exit numbers. Connecticut planned to convert I-91 to mileage-based exit numbering in 1974; however, 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 since 2003 (and newer exits use numbers making no sense to either system, such as Exit 86 in Frederica not being 86 miles or kilometers from the Maryland line), and I-295 has no exit numbers at all, however, DelDOT has made a reference on a 2016 construction notice referring to the exit to I-495 north as "Exit 2".
- District of Columbia – Historically, the only exit numbers posted in the District consisted of sequential numbers on I-295. The other freeways within the District of Columbia did not have exit numbers, but in 2008 the District began posting sequential numbers on I-395. As of June 2008[update], 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 – Sequential (experimented with dual exit/mile tabs in the 1970s). A contract (MassDOT Project 608024) to change over most highways to mileage-based has been awarded. The Massachusetts Turnpike (I-90) will have its exit numbers changed as part of scheduled sign replacement work to occur at the same time. Work was to start in January 2016 to convert highway exit numbers, first in the western part of the state then working eastward (except for numbers on the Mass. Turnpike/I-90 which will be changed under MassDOT Projects 606619 and 606712) with a completion date for the entire project of early 2018. However, it appears the start of work is now on hold, with no specific start date announced. This appears to be the results of feedback from politicians and the public after news of the project got out. Officials on Cape Cod were publicly critical of MassDOT's plan (see this article in the Cape Cod Times) and the State Highway Administrator, Tom Tinlin is quoted in a Worcester Telegram & Gazette article in February saying he had not yet signed off on the project. On April 27 it was reported that the numbers on US 6 would not be changed and that the rest of the project was still being evaluated.(2) In April, MassDOT announced the winning bidder for a project to replace exit signs on I-495. The contract was modified to include a clause whereby the state would inform the contractor whether to use milepost based numbers or keep the sequential numbers for the new signs. Based on a website forum comment from a MassDOT sign engineer, this clause has now been included in contracts already awarded to replace exit signs along the Mass Pike, both of which are now underway. (3) It may not be until the end of the summer whether the public will hear a final word on whether or not the project is proceeding. When/If the project starts it will not change exit signs, but will replace the numbers on the exit tabs. Massachusetts and New Hampshire are among the states still using sequential numbering that initially requested a waiver from the Federal Highway Administration to retain sequential exit numbering system indefinitely. This request was denied by FHWA. In June 2016 Massachusetts had asked the FHWA to reconsider its initial denial of a waiver to retain sequential exit numbering, citing widespread opposition from residents, businesses and elected officials to convert to distance-based exit numbering.
- Maryland – The Baltimore Beltway is sequentially numbered.
- New Hampshire – All sequential. New Hampshire DOT has reportedly received permission to use Federal funding to convert to mileage-based, but has yet to announce a formal plan for conversion.
- New Jersey – Sequential numbering on the New Jersey Turnpike, Palisades Interstate Parkway, and I-676. Other New Jersey exit numbering is mile-based, except for the Brigantine Connector in Atlantic City, which uses letters for exits. Many New Jersey freeways lack exit numbers.
- New York – Sequential, except I-781 (Fort Drum spur), I-890 in Schenectady, and I-95 south of the Pelham Parkway. The recently opened section of I-99/US 15 also has mileage-based numbers.
- Rhode Island – Sequential; experimented with dual exit/mile tabs in the 1970s. The state was denied a waiver from the FHWA to retain its sequential numbering system.
- Vermont – Sequential, except Route 289 (Circumferential Highway), which has mileage-based exit numbering.
Most states began with sequential numbers, while California numbered few exits during the 20th century:
- California – Began January 2002, although some exits in Los Angeles received mile-based numbers in the 1970s. 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. Originally, the initial completion date for installing exit numbers statewide was set as November 2004. But because of California's budget woes, exits (especially in the Greater Los Angeles and San Francisco Bay areas) have generally been numbered only when signs needed to be replaced. The state may eventually replace all older overhead signs (and thus add exit numbers) as part of an energy-saving measure: in 2014, Roads & Bridges reported that the California Department of Transportation was testing types of reflective sheeting to eliminate the need for electrical-sign lighting.
- Colorado – Initially sequential; used dual mile/sequential plates in the mid-1970s.
- Connecticut – Started a gradual transition from sequential to mileage-based exit numbers in 2015, with secret CT 695 and I-395 converted that year, and Route 2A in early 2016 under the same contract. The next freeways to be converted to mileage-based exit numbering will be Routes 8 and 25, with both projects scheduled for completion in 2017. The Connecticut Department of Transportation let one contract to replace signage and renumber exits on the Route 25 freeway north of the Route 8 split in July 2015, and a second contract for Route 8 in September 2015. Exit numbers on other highways will be converted to mile-based numbering over a 20-year period as existing highway signs reach the end of their serviceable life and are replaced with new signage.
- Florida – Began January 28, 2002; now complete. However, I-110 retained its sequential exit numbers.
- Georgia – Began January 4, 2000, now complete; no "former exit" signs were used in the renumbering. (Interstate highways only).
- Indiana – Around 1980. Exits on I-69 between Indianapolis and the Michigan state line underwent a second renumbering in 2012, when the first portion of the I-69 extension to Evansville opened that year.
- Iowa – Adopted distance-based exit numbering in 1977.
- Maine – Early 2004 (experimented with dual exit/mile tabs in the 1970s).
- Massachusetts - Exit renumbering was scheduled to start in January 2016 with completion slated for early 2018 but is now on hold with no specific start date announced.
- Mississippi – 1980s.
- New Jersey – Around 1970. The New Jersey Turnpike kept sequential exit numbering.
- New York – New interstates (I-781 and I-99) have mileage-based exit numbers. The New York State Department of Transportation, which had replaced mile-based exits with sequential on I-95 in New York City, reverted to distance-based. The state has no timeline for converting its remaining highways to mileage-based numbering. Bills directing the NYSDOT and the New York State Thruway Authority to renumber exits from sequential to mile-based have been introduced into the state legislature since 2008; none of which have been approved by both chambers.
- North Dakota – 1980s
- Ohio – Interstate 475 was its first highway to receive mileage-based exit numbers, in October 1974. The Ohio Turnpike used both systems from January 1998 to September 2002.
- 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. Signage approaching many interchanges still includes former sequential numbers on "Old Exit XX" placards below the exit signs.
- Rhode Island - Transition will occur in four phases starting in 2016, with the full conversion scheduled for completion by the end of 2019.
- Texas – late 1970s
- Virginia – Early 1990s; exceptions include Route 267 (suburban Washington, D.C.), Interstate 581 (Roanoke), and Interstate 664 (Newport News - Chesapeake). I-581 and I-664 both utilize sequential exit numbers; furthermore, Exit 1 is at the highways' northern ends.
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 (since 2003) when the metric-based posts were replaced, and several newer exit numbers (86, 91, 98) 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.
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.
- Alabama: only on U.S. Route 78 (future Interstate 22).
- In Arizona, many of its non-interstate freeways utilize exit numbers such as the freeway loops (Arizona State Highway 101 and Arizona State Highway 202) around Phoenix, U.S. Route 60 and Arizona State Route 51.
- In Arkansas, U.S. Route 67 and State Highway 549 are the only non-interstate freeways to have exit numbers.
- California uses exit numbers on all of its non-interstate highways statewide when they are built to freeway standards. However like its interstate highways (as stated above), the state's budget woes have caused exits on these routes to only be signed with numbers when signs need to be replaced.
- Colorado does not use exit numbers on non-interstate highways. The exception is E-470 and the Northwest Parkway, which are separate toll highways.
- Connecticut uses sequential exit numbers on longer non-interstate freeways, such as CT Routes 2, 8, 9, 11, 25, 40, and 72, but will eventually transition to distance-based exit numbers. Exit numbers on Route 2A are distance-based. Exit numbers on Route 15 (Merritt and Wilbur Cross parkways) are sequential; CT 15's exit numbers are a continuation of exit numbers from the Hutchinson River Parkway in New York, except that the Route 120A interchange on the state line is Exit 30 eastbound, and Exit 27 westbound. The Wilbur Cross Parkway, eastbound, takes over the Merritt's sequential numbering. Freeway sections of US 7 also use sequential numbering. Shorter freeway sections, such as the US-6 Windham Bypass, Route 20 (Bradley Airport Connector), and freeway sections of Route 17 lack exit numbers.
- In Florida, the Turnpike and other expressways owned and operated by the Florida Turnpike Enterprise use distance-number exits. Toll roads under the Central Florida Expressway Authority also use distance-number exits. The Lee Roy Selmon Expressway in Tampa uses a sequential-based exit numbering system. Expressways under the authority of the Miami-Dade Expressway Authority have no exit numbers.
- Georgia does not carry exit numbers on non-interstate expressways except for the Georgia 400 and Stone Mountain Freeway, which run on a sequential system, and Georgia State Route 10 Loop, running on a distance-numbers system.
- In Illinois, the Illinois Tollway system has begun numbering exits. They plan to all be numbered by the end of 2010.
- A number of small cities in Kentucky, mainly in the southeastern and south-central portions of the Commonwealth, mark traffic lights on a main commercial road with sequential numbers, usually beginning at an intersection with a primary highway:
- Berea — KY 21, starting at the I-75 interchange until KY 21 meets US 25. Numbering continues on US 25 until the road leaves the city limits. Throughout this stretch, numbering increases as one travels north.
- Corbin — US 25E, starting at the I-75 interchange at North Corbin and continuing for approximately 5 miles (8 km) until its intersection with KY 830 east of Corbin. Numbering increases as one travels east (which is signed as south on 25E).
- London has two sets of numbered lights. The Hal Rogers Parkway, starting at KY 192 (which is not numbered, as it is a flashing yellow light for parkway traffic instead of a fully controlled signal) and ending at US 25, uses increasing westbound numbering. KY 192, starting at the I-75 interchange, uses increasing eastbound numbering until the Hal Rogers Parkway.
- Manchester — US 421, starting at the Hal Rogers Parkway and increasing as one travels north through the city.
- Middlesboro — KY 74 through the downtown area, with numbering increasing as one travels west.
- Monticello — KY 90, starting at the northern end of the city and increasing until exiting the city.
- Radcliff — US 31W, also known as Dixie Highway, starting at an intersection at the city's border with Elizabethtown and increasing as one travels north until reaching the main entrance to Fort Knox.
- Richmond also has two sets of numbered lights. U.S. Route 25 Business uses exit numbers through downtown numbers lights 1–6 from KY 52 at Lancaster Avenue and the next 5 consecutive lights south; however, the lights south of the railroad tracks and north of the KY 52 multiplex are not numbered. The bypass route wrapping east around Richmond uses exit numbers from KY 876 (locally known as Eastern Bypass) east of I-75 exit 87, and continues onto Dr. Robert R. Martin Highway US 25/US 421 to I-75 exit 90; however, the traffic lights at the interstate are not numbered.
- Somerset — US 27, starting at the northern limits of the city and increasing as one travels south. The numbering continues even after the road leaves the city limits, with the final numbered intersection occurring shortly before US 27 enters the city of Burnside.
- In Maryland, there are three state highways that use exit numbers. Maryland Route 200 continues the distance-based exits from its parent Interstate 370. Maryland Route 32 has a peculiar distance-based exit set up in that the exits are numbered from east to west from Interstate 97 to Maryland Route 108 so that the eastern terminus of MD 32 starts at mile 0. Maryland Route 100 uses distance-based exits until Edwin Raynor Blvd (Exit 20).
- Maine has exit numbers only in Interstates; its other limited-access highways with limited exceptions lack mile markers.
- Minnesota distance-numbers its exits on Interstates, but leaves other freeways or expressways with unnumbered exits. The first exception was US 52's freeway portion through Rochester, which received mileage-based exit numbers in 2004 as part of a major widening project. Since then, exit numbers also started appearing on US 169 in Shakopee in 2016.
- In Mississippi, exits from Interstate 69 and non-Interstate freeways are not currently numbered, with the exception of U.S. Highway 78/future Interstate 22, which received exit numbers as part of a signing replacement project in 2002.
- In Missouri, non-Interstate Highways do not have exit numbers, the exceptions being Route 364 and Route 370 in St. Charles and St. Louis counties, which use mile-based exit numbers.
- New Hampshire does not assign numbers to exits to junctions with Interstates (with the exception of I-393 in Concord, in which exit 15W from I-93 connected to the US 4/US 202 interchange prior to the construction of I-393). For example, I-293's southern exit from I-93 is between exits 5 and 6, but is not numbered; NH-101 eastbound, however, despite being an interstate grade freeway, is assigned Exit 7. NH-101's own exit to Interstate 95 in Hampton is between exits 12 and 13, but is also not numbered.
- In New Mexico, U.S. 84/285 between Pojoaque and Santa Fe was the first non-Interstate highway in New Mexico to use exit numbers. The NM 599 and Santa Fe County Road 62 interchange, which was completed in mid-2013, is the only non-freeway within New Mexico using an exit number (Exit 6). The US-70/285 Relief Route around Roswell has an interchange with two exits marked "Exit A" and "Exit B." Other freeways (US-70 east of Las Cruces and NM 423 in Albuquerque) have no exit numbers due to their relatively short lengths.
- In New England, except for Maine (which assigned exit numbers based on mileage), exit numbers are posted on express highways of any significant length, regardless of designation. Some at-grade intersections have posted numbers; such as on CT 9 in Middletown.
- In New York, most highways in the New York City metro region of this type use sequential numbering (an exception is the Belt Parkway system, which uses directional suffixes (N, S, E, W) and alphabetical suffixes.) Expressways and freeways without interstate designations upstate have unnumbered interchanges. In addition:
- All parkways on Long Island, except the Southern State Parkway, Heckscher State Parkway, and Northern State Parkway preface exit numbers with a one or two letter prefix indicating the parkway's name. For example, exits on the Meadowbrook Parkway are numbered M1 through M10, and exits on the Sunken Meadow Parkway are numbered SM1 through SM5. Some of these exits have a letter suffix as well (usually N, S, E, and/or W).
- Some at-grade intersections (level junctions) have posted numbers; former examples are the Taconic State Parkway, NY 17, and within New York City, NY 27 along only the section of Linden Boulevard east of Kings Highway. Current examples are the Bronx River Parkway and, within New York City, NY 27 along Conduit Avenue only.
- The Taconic State Parkway formerly numbered exits and at-grade intersections sequentially by county, with a one-letter prefix indicating the county. Interchanges in Westchester County were prefixed with W (e.g., W5), Putnam with P, Dutchess with D, and Columbia with C.
- Exits on the Berkshire Spur (part of which is I-90) of the New York Thruway are B1, B2 and B3, as the spur is part of the mainline ticket system. (Exits 1, 2, and 3 on the mainline Thruway are in Yonkers.)
- In Ohio, exits on non-Interstate highways generally go unnumbered. However, Ohio Department of Transportation District 2 has begun to employ exit numbers on non-Interstates using the south or west entrance into the state or highway beginning as the point of origin, and District 3 measures them from the south or west entrance into the respective county.
- Oklahoma posts exit numbers on its tollway system.
- Oregon originally did not post exit numbers on any of its non-Interstates. In the 1990s, the Oregon Department of Transportation began numbering most sections of its freeways with mile-based exits, starting with US-26 and OR-217 west of Portland. As of 2013, almost all Oregon freeway interchanges are numbered; new interchanges are also numbered. (These exits are based on internal limited-access road mileage; see State highways in Oregon for an explanation on these differences.)
- Pennsylvania's non-Interstate highways that have numbered exits are still numbered sequentially, with the exception of the toll roads that are part of the Pennsylvania Turnpike system. PA 60 was one of these roads, but the numbers were converted to the mileage-based system (since reversed) in November 2009 when I-376 was extended along PA 60 to Mercer County. The Pennsylvania Turnpike Northeast Extension, opened in 1957, originally had a unique system in which the mileposts were separate from that of the mainline turnpike, starting at milepost A0.0 (the mainline turnpike went from 0.0 to roughly 359.0), but used the sequential exit numbers 31 to 39 (the mainline turnpike went from 1 to 30). Upon the conversion to the mile-based system, the mainline turnpike uses the distance of I-76 from the Ohio state line to New Jersey (as I-276), while the Northeast Extension was converted in 2000–2003 using the mileage based on the southern junction of I-476 (with I-95 in Chester), with the southernmost Northeast Extension exit being numbered as Exit 20, using the I-476 mileage instead of Exit 333A or Exit 334 on the east–west mileage, thus making the highways separate, but distinct systems despite the use of the common ticket system. (Coincidentally, Exit 31 for Lansdale kept its original number being between Mile 30 and 31 when the extension was renumbered for I-476's mileage.) Additionally, freeway sections can have independent mileposting systems that apply exclusively to the freeway: an example of this being the Robert Casey Highway-US 6 extending northeast of Scranton, which has mileposts reflecting the length of the freeway section. Conversely, the US 22 Lehigh Valley Thruway through Bethlehem and US 30 between York and Lancaster have no exit numbering, but do have mileposts that reflect the appropriate distance from the Ohio border.
- Tennessee generally does not post exit numbers on its non-Interstate freeways, with the exception of Nashville's two non-Interstate partial beltways: TN 155 (Briley Parkway) and I-840.
- Texas currently has three non-interstates that use exit numbers. US 75 uses a sequential scheme. Due to a major reconstruction project in the 1990s, which combined many exits, these jump from 8B to 20B. Similarity, US 54 in El Paso uses sequential exits, starting at exit 20. SH 130 uses mile-based exits starting at 497 and decreases to 411 at its northern terminus. Exits on completed sections of Interstate 69 around Houston are currently unnumbered. Exits on other freeways are based off a statewide reference system where the exit number is determined by the distance from either the northernmost (northwest corner of the Texas Panhandle) or westernmost (Texas/New Mexico/Mexico tripoint, near El Paso) geographic reference point in Texas.
- Vermont does not use the mileage-based system on non-Interstates, with two exceptions: VT 127 and VT 289 in the Burlington area. The numbers would have been continuous if the Chittenden County Circumferential Highway were completed. The numbers start at Manhattan Drive just north of Burlington and end at Interstate 89 near Williston. Freeway sections of US-4 and US-7 in the western part of the state use sequential numbering.
- Washington state does not number most of its non-Interstate freeway exits. Two exceptions are SR-14 from Vancouver to Camas (since the 1990s) and SR-16 from Tacoma to near Gig Harbor (since 2006, possibly to extend along all of SR-16 to its northern terminus in Gorst), both milepost-based. It is unclear if other freeways will receive numbers in the future.
- West Virginia has only one non-interstate with exit numbers, the US 22 freeway in Weirton.
- Wisconsin has exit numbers on the freeway and expressway portions of US 12 WIS 16, WIS 29, WIS 64, US 41, US 45, US 51, US 53, WIS 145 and US 151.
Early exit numbers
- In April 1938, the New York City Department of Parks installed exit numbers on New York City's parkways, specifically:
- Grand Central Parkway – 1 at Triborough Bridge to 11 at Kew Gardens, and on to 24 at Marcus Avenue, then continuing from 25 (Lakeville Road) on the Northern State Parkway (run by the Long Island State Park Commission, which also planned numbers on its other parkways)
- Interborough Parkway (now the Jackie Robinson Parkway) – 4 at Pennsylvania Avenue to 11 at Kew Gardens (Exits 1, 2, and 3 were intended for a formerly proposed extension to Belt Parkway)
- Henry Hudson Parkway – 1 at 72nd Street to 19 at Mosholu Parkway
- Hutchinson River Parkway – beginning with 7 in Pelham Bay Park
- As other New York-area parkways were completed, they too got numbers.
- Connecticut's Merritt Parkway (CT-15) got sequential numbers in 1948, continuing the numbers of the Hutchinson River Parkway. The Merritt Parkway's lowest-numbered exit remains Exit 27, although the "Hutch" exits were renumbered; traveling towards Connecticut, Exit 30 is encountered at the border (also the beginning of Route 15), where the number "resets" to 27 before reascending. The remainder of Route 15's exit numbers (on the Wilbur Cross Parkway and Wilbur Cross Highway) continue the Merritt sequence.
- The Pennsylvania Turnpike had sequential numbers when its first section opened on October 1, 1940.
- The New Jersey Turnpike had sequential numbers when it opened in late 1951.
- In the early 1950s, New Jersey's Garden State Parkway opened, probably the first road to use distance-based exit numbers.
- The Gulf Freeway (US 75, later Interstate 45) in Houston, Texas had sequential numbers by 1956. The numbering scheme started at the freeway's northern end in downtown Houston, and counted up towards the southeast and Galveston.
- Massachusetts started handing out exit numbers in the 1950s to its freeways in and around the Boston area, with an uncommon system of making sure every freeway's intersection with Route 128 was an "Exit 25", numbers increasing away from Boston. Starting in 1976, these freeways started to receive more conventional numbering. As of 2007, only the US 3 freeway retains its original numbering with the older system, to avoid exit confusion with MA 3, whose northernmost non-multiplexed numbered exit is 20.
- California Highways: Numbering Conventions – Postmiles. Accessed: 17 July 2008.
- Brown, Patricia Leigh. "Counting the way to San Jose." New York Times, 10 February 2002, sec. WK, p. 2.
- "California Highways: Numbering Conventions Exit Numbers". Retrieved 2009-03-05.
- Proposed Amendements to the MUTCD Section 2E.27 Lines 33–41
- MUTCD 2009 Edition Introduction, Paragraphs 22 through 24 and Table I-2
- Exit Numbering, www.kurumi.com, Accessed Nov 15, 2009
- I-395 Exit Re-Numbering Will Create Problems, Montville Patch, May 16, 2013
- Röckers Meet King Tubbys Inna Fire House[dead link]
- Upstate New York Roads – Interstate 890 Interchange Guide
- Lozier, Marcia (January 3, 2014). "Caltrans tests reflective sheeting for guide-sign visibility and cost savings". Roads & Bridges. Retrieved October 8, 2015.
- Bid Results, Connecticut Department of Transportation, Accessed December 30, 2015
- Operations – Florida's Interstate Exit Numbers
- Georgia DOT – Interstate Exit Numbers
- "I-475 Exits To Conform To Mileposts". The Blade. 138. Toledo, Ohio. August 7, 1973. p. 17 – via Google News Archive.
- "Turnpike interchange numbers start changing after Labor Day". The Bryan Times. 54 (125). Bryan, Ohio. May 28, 2002. p. 10 – via Google News Archive.
- "Turnpike signs will be changing". The Bryan Times. 54 (217). Bryan, Ohio. September 14, 2002. p. 7 – via Google News Archive.
- Holley, Denise (March 17, 2009). "New signs on Interstate 19 courtesy of recovery funds". Nogales International. Retrieved 2009-12-29.
- "Florida Department of Transportation Interchange Report" (PDF). Florida Department of Transportation. 2008-11-24. Retrieved 2009-07-27.
- Patch, David (February 10, 2007). "ODOT extends numbered exits to noninterstates". The Blade. 157 (41). p. B1. Archived from the original on February 10, 2007. Retrieved September 28, 2009.
- "Lorain County Photos: OH 2 through Lorain County". Roadfan.com.
- US 22 at Weirton Archived January 8, 2008, at the Wayback Machine.
- Wisconsin Department of Transportation. "Exit Numbers on Wisconsin's Freeways". Retrieved 2007-12-06.
- Merritt Parkway (CT 15)
|Wikimedia Commons has media related to Exit number road signs in the United States.|
- Signs Numbering Exits Installed on Parkways, New York Times April 24, 1938 page 26