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(詳細はUnited States, exit numbers are assigned to road junctions, and are usually numbered as exit from a freeways. It is usually marked on the same sign as the destinations of the exit, as well as a sign in the gore. Exit numbers typically reset at political borders such as state lines, and some non-freeways use exit numbers. Road exits in the United States are usually numbered in two formats: distance-based and sequential. ==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.〔(California Highways: Numbering Conventions – Postmiles ). Accessed: 17 July 2008.〕 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.〔Brown, Patricia Leigh. "Counting the way to San Jose." ''New York Times'', 10 February 2002, sec. WK, p. 2.〕 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.〔(【引用サイトリンク】 title=California Highways: Numbering Conventions Exit Numbers )〕 Nine states 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,〔(Proposed Amendements to the MUTCD ) Section 2E.27 Lines 33–41〕 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.〔(MUTCD 2009 Edition ) Introduction, Paragraphs 22 through 24 and Table I-2〕 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 (beginning in June 2015); these number changes are on the former Connecticut Turnpike. (The sign-replacing contract also includes CT Route 2A and "secret" CT 695; the latter also part of the former 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.〔(Exit Numbering, www.kurumi.com, Accessed Nov 15, 2009 )〕〔(I-395 Exit Re-Numbering Will Create Problems, Montville Patch, May 16, 2013 )〕 * 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. * 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. , 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.) Contracts to changeover to Mileage-based have been released, with plans to make the change in 2016/2017. Massachusetts had originally requested a waiver from the Federal Highway Administration to retain its sequential exit numbering system indefinitely. * Maryland – The Baltimore Beltway is sequentially numbered.〔(Röckers Meet King Tubbys Inna Fire House ) 〕 * New Hampshire – All sequential. * 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 Interstate 781 (Fort Drum spur), I-890 in Schenectady,〔(Upstate New York Roads – Interstate 890 Interchange Guide )〕 and I-95 south of the Pelham Parkway. The recently opened section of Interstate 99/US 15 also has mileage-based numbers. * Rhode Island – Sequential; experimented with dual exit/mile tabs in the 1970s. The state has requested 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 other states began with sequential numbers and switched over later. Here is a list of these switches: * 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. 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 only been signed with numbers when signs need to be replaced. The state may eventually replace all older overhead signs (and thus add exit numbers) statewide 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 – Used dual mile/junction plates into the mid 1970s; initially used sequential numbering. * Connecticut – Started a gradual transition from sequential to mileage-based exit numbers in 2015, with I-395 the first freeway converted in June of that year; CT Route 2A also will be converted as part of the same contract. The Connecticut Department of Transportation let a similar contract to replace signage and renumber exits on the Route 25 freeway north of the Route 8 split in August 2014. (Exit numbers on the Route 25/8 concurrency will not be changed in this project.) Contracts to replace signs and renumber exits on Route 8 are scheduled to be awarded in phases between late 2015 and early 2016.〔(Advertising Schedule of Projects, Connecticut Department of Transportation, Accessed January 22, 2014 )〕 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.〔(Operations – Florida's Interstate Exit Numbers )〕 * Georgia – Began January 4, 2000, now complete.〔(Georgia DOT – Interstate Exit Numbers )〕 (Interstate highways only). * Indiana – Around 1980. * Iowa – May have had sequential numbers on Interstate 80 in the early 1970s. Adopted distance-based exit numbering in 1977. * Maine – Early 2004 (experimented with dual exit/mile tabs in the 1970s). * Massachusetts - Exit renumbering scheduled to start in 2016 with completion slated for 2017. * Mississippi – 1980s. * New Jersey – Around 1970. The New Jersey Turnpike kept sequential exit numbering. * New York – Recently completed freeways, notably I-781, I-890, and I-99, have mileage-based exit numbers. Additionally, the New York State Department of Transportation began changing exit numbers on I-95 through New York City from distance-based to sequential, but then reverted to distance-based in anticipation of an eventual conversion to solely distance-based numbering throughout the state. Currently, New York has no timeline for converting its remaining highways to mileage-based numbering. Bills directing the New York State Department of Transportation and the New York State Thruway Authority to renumber exits from sequential to mile-based have been introduced into the New York state legislature since 2008, none of which have been approved by both chambers and signed into law. * North Dakota – 1980s * Ohio – Interstate 475 was the first highway to receive mileage-based exit numbers, in October 1974. The Ohio Turnpike carried 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. * Texas – late 1970s * 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. 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Exit numbers in the United States」の詳細全文を読む スポンサード リンク
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