Exit number
An exit number is a number assigned to a road junction, usually an exit from a freeway. It is usually marked on the same sign as the destinations of the exit. In some countries, such as the United States, it is also marked on a sign in the gore. Exit numbers typically reset at political borders such as state lines. Some non-freeways use exit numbers. Typically these are rural roads built to expressway standards, and either only the actual exits are numbered, or the at-grade intersections are also numbered. An extreme case of this is in  New York City, where the Grand Concourse and Linden Boulevard were given sequential numbers, one per intersection (both boulevards no longer have exit numbers as of 2011). A milder version of this has been recently used on the West Side Highway, also in New York, where only the major intersections are numbered (possibly to match the planned exits on the cancelled Westway freeway). Another case is the Nanaimo Parkway in Nanaimo, British Columbia carrying Highway 19, where all exits are numbered though all except one are at-grade intersections. Some other intersections on Highway 19 outside Nanaimo are also given  numbers. As a means of educating motorists, some state highway maps include a brief explanation of the exit numbering system on an inset. Iowa DOT maps from the 1980s and 1990s included a picture or drawing of a milepost and briefly described how Iowa had included milepost references near interchanges on the map. Sequential numbers. Sequential exit numbering usually begins with exit 1 at the beginning of the road; each subsequent exit is given the next number. Letter suffixes are commonly used when new exits are added. For example, on the New York State Thruway, an exit was added between  21 and 22, and was given the number 21A. Subsequently, a new exit was added between 21 and 21A, leading to the sequence 21 - 21B - 21A - 22. In Florida, some new exits got the suffix C, so that if it had or acquired separate exits for the two directions, they would be 15CA and 15CB rather than 15AB. There are also occurrences of this happening on the New Jersey Turnpike; the original interchanges opened in 1951, with newer exits as recently as 1982. On the Baltimore Beltway, there is an exit 12B-C (MD 372), as well as 12A (US  1). There is also an exit 8A (I-895) and an exit 8 (MD 168). Some sequential exits are renumbered (remaining sequential) due to added exits. For instance, the Hutchinson River Parkway in New York was renumbered so that its northernmost exit, 27, became 30. However, the Merritt Parkway, which continued the Hutchinson's exit numbers in Connecticut, was not renumbered. This means the Route 120A interchange is numbered 27 in Connecticut "and" 30 in New York. The Atlantic City-Brigantine Connector in Atlantic City, New Jersey uses letters (without numbers) for its exits; it has many exits in a short  distance, and the South Jersey Transportation Authority may have wanted to avoid numbers, as the Atlantic City Expressway's lowest numbers (mile-based) are in Atlantic City. Distance-based numbers. As more highways were built, states and countries began to experiment with distance-based (mile-based or kilometer-based) exit numbers. The first mile-based system known was implemented on the Garden State Parkway in New Jersey in the late 1950s. Michigan also implemented mile-based junction numbers on Interstate 94 in the 1960s. In this system, the number of miles from the beginning of the highway to the exit  is used for the exit number. If two exits would end up with the same number, the numbers are sometimes modified slightly; this is often impossible and exits are given sequential or directional suffixes, just as with sequential numbers. An exit can be numbered by where the exit in the direction of increased mileage leaves the freeway, or by where the road that the exit serves crosses the freeway (which is occasionally ambiguous). From this number, the integer exit number can be determined by rounding up, rounding down, or rounding to the nearest integer. Many jurisdictions prefer to avoid an  exit 0. To this end, the numbers are either rounded up to get the exit number, or any exit that would get the number 0 is instead numbered 1. Examples of highways with an exit 0 are British Columbia Highway 1 on the mainland, Interstate 70 in Wheeling, West Virginia, along the West Virginia–Ohio border, and Interstate 90 on the Montana side of the Idaho–Montana border. Some freeways' exit number starts from an advanced number (i.e. higher than 1). One reason for starting with a number higher than 1 is that the maintaining agency expects that the highway  will be extended. For example, Ontario Highway 400 starts at 20 because it was expected that the southern end of the highway would extend to downtown Toronto (which was never built). Another reason to use a higher number is that the freeway is branching off from another freeway. An example is British Columbia Highway 5, which branches off British Columbia Highway 1 and starts at 170. In areas that use the metric system, distance-based numbers are by kilometer rather than mile. A few highways, such as Delaware Route 1 and Interstate 19, have kilometer-based exit numbers, even in  areas that typically use miles. Exit numbers by country. Australia. Distance-based exit numbering is used in Queensland, although there is not a consistent approach for defining the datum. For example exit numbers may increase from south to north or north to south. Victoria and New South Wales have partially implemented sequential exit numbering on selected urban motorways. For instance, the M31 Hume Motorway in New South Wales has exit numbering between Prestons and Campbelltown. Europe. Most European countries use sequential numbering schemes. Spain uses distance-based numbering on its Autovias, but not on its Autopistas. Austria, the Czech Republic , Hungary and Slovakia use distance-based schemes. A number of European countries (including the Netherlands, Belgium and France) do not number motorway intersections, apparently because one cannot "exit" the motorway there. Countries like Germany and Switzerland have attributed numbers to their exit, but instead of the usual exit symbol, they are given a specific interchange symbol. Italy uses sequential numbering on the ring roads for some cities, including the ring road of Rome ("GRA") and Milan ("Tangenziali"). At one time, it referred to junctions on the Autostrada del Sole by number, and published same on toll tickets; though these  may not have been posted on signs. Both the United Kingdom and the Republic of Ireland use sequential numbering systems, with the junction number indicated by a white number in a black square in the corner of signs. In the United Kingdom they are frequently referenced in the media as the number with "J" on front of it, with for example Junction 1 being referred to as "J1"; as such this abbreviated term has entered popular usage. If a junction is newly constructed to between two existing junctions, it is normally allocated the number of the lower of the two  junctions, with the letter "A" attached (and so on). For example, a new junction opened between Junctions 3 and 4 would become Junction 3A. In the Republic of Ireland, junction numbers have existed since the opening of the first section of the M50 motorway in 1990, however due to the short length of Irish motorways until the early 2000s they were normally ignored by the general public. They are beginning to come into popular usage now, and since 2005 have been given greater prominence on road signs. With the development of the inter-urban motorway network under the National Development  Plan and Transport 21, the National Roads Authority has adopted a numbering scheme for the inter-urban roads that will see Junction 1 being designated as that road's junction with the M50 in most cases. This has meant renumbering of existing junctions on some motorways, most notably the M7 motorway. Non-motorway dual carriageways forming part of major inter-urban roads also have junction numbers, however only grade-separated interchanges are numbered. The United Kingdom uses sequential numbering in part because motorway signs use miles rather than kilometres; there are no formal plans to metricate the country's motorway  system. Canada. Most Canadian provinces use kilometre-based exit numbers. Sequential numbers are used only in Nova Scotia, and Newfoundland and Labrador. The territories of Yukon, Nunavut, and Northwest Territories use no exit numbers, as there are no freeways or expressways in the territories. Prince Edward Island has no exit numbers either, as there is only one interchange in the province, the Albany Corner interchange near Borden-Carleton. Hong Kong. Exit numbers were introduced to major Hong Kong routes in 2004, in conjunction with the re-organization of the route numbers. A sequential numbering scheme is used. Japan. The main  expressway system uses sequential numbering; Metropolitan Expressway systems also use sequential junction numbering, usually appended with the expressway number expressed thus: 5-1; 5-2, etc. There are multiple toll expressways not operated by the major national syndicates or the Metropolitan Expressway Authorities that have no junction numbering scheme. New Zealand. New Zealand began introducing exit numbers in the Auckland region in 2005. It uses a distance-based numbering system. The distance to the exit is measured from the origin of the highway. That is: There is no exit zero. If there is an exit within 1.499 km of the  origin, Exit 1 is used. Exit 2 would be between 1.500 and 2.499 km of the origin. Subsequent 'exit zones' are at 1 km intervals. Letter suffixes are added at multi-exit interchanges, or where two or more exits exist within the same exit zone. For example, State Highway 1 (Southern Motorway) has an Exit 429A (Symonds St), Exit 429B (Wellesley St) and Exit 429C (Port). Instead of replacing existing ramp and link signs, the exit numbers were added as supplementary information. Thus drivers can navigate either by exit number or name. Exit numbers are only used for exits that  may be used by all vehicle types. Bus- or emergency vehicle-only exits would not be numbered. Exit numbers are not used outside the Auckland region. Philippines. Metric distance based numbers are used on the tollways radiating from Manila. Supplemental "A" and "B" designations are appended to signage at the ends of slip roads. Expressway signage, exit number signs, and kilometer markers mostly replicate Australian and American freeway signage. South Africa. Uses distance based numbering (in kilometers) on main motorways. Letter suffixes are added at multi-exit interchanges, an example being the Buccleuch interchange in Johannesburg. Exit numbers are reset  on the borders of the provinces as they were until 1994. This means that exit numbering may change in the middle of a province. One exception to the usual distance based numbering is the southern portion of the M4 in Durban, which uses sequential numbering. Taiwan. Taiwan uses distance-based exit numbers in kilometers. If two exits are located within the same kilometer mark, the Roman letters are appended to differentiate the exits. Taiwan did experiment with sequential exit numbers with National Freeway No. 1 for a couple of years, but abandoned the experiment in 2004. Prior to 2006, Taiwan  exit signs were generally near replicas of their US counterparts. However, the exit signs now not only indicate the distance number, but they also display the Chinese code-name for the interchange.