Editing Exit number (section)

==Distance-based numbers==<!-- This section is linked from [[Distance]] -->
[[File:2019-05-27 16 23 47 View south along the outer loop of the Capital Beltway (Interstate 495) at Exit 40 (Cabin John Parkway, Glen Echo) on the edge of Bethesda and Potomac in Montgomery County, Maryland.jpg|thumb|right|Exit 40 along the [[Capital Beltway]] (I-495) circling Washington, D.C., which is located at milepost 40]]
[[Image:Quebec exit number.jpg|thumb|right|An exit sign (kilometer-based) on [[Quebec Autoroute 640]] in Quebec]]
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 Michigan|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; unless there are too many in proximity, and exits are given sequential or directional suffixes, just as with sequential numbers. Distance based numbering is the norm for most highways in the United States and Canada. Many jurisdictions in North America began switching to distance based in the 1980s, with some projects still ongoing currently to convert towards a distance based system. These are further complemented by mile markers or KM markers.

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.{{efn-la|While the [[Federal Highway Administration|FHWA]] allows exits that are numbered "0", they do not require its use. For example, the 
[[Massachusetts Department of Transportation]]<ref>{{Cite web |title=Statewide Exit Renumbering Project Details |website=Mass.gov |url=https://www.mass.gov/info-details/statewide-exit-renumbering-project-details |access-date=2023-12-22 }}</ref> and the [[Connecticut Department of Transportation]]<ref>{{Cite web |title=Frequently Asked Questions (Exit Renumbering) |website=CT.gov |url=https://portal.ct.gov/-/media/dot/documents/dtrafficdesign/exit_renumbering_faq.pdf |access-date=2023-12-22 }}</ref> both have chosen not to incorporate these exits statewide.}} 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 West Virginia|Interstate 70]] in [[Wheeling, West Virginia]], along the West Virginia–Ohio border, and [[Interstate 90 in Montana|Interstate 90]] on the Montana side of the Idaho–Montana border.<!--three examples are sufficient. this is NOT an exhaustive list; rather it is just an illustrative one.-->

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 number of highways have kilometer-based exit numbers, even in areas that typically use miles; an example of this is with [[Interstate 19]] in the US state of Arizona.