Editing Interstate Highway System (section)

===Exit numbering===
{{more citations needed section|date=June 2011}}
The majority of Interstates have [[exit number]]s. Like other highways, Interstates feature [[Road signs in the United States#Guide signs|guide signs]] that list [[control cities]] to help direct drivers through interchanges and exits toward their desired destination. All [[Road signs in the United States|traffic sign]]s and [[lane]] markings on the Interstates are supposed to be designed in compliance with the [[Manual on Uniform Traffic Control Devices]] (MUTCD). There are, however, many local and regional variations in signage.

For many years, California was the only state that did not use an exit numbering system. It was granted an exemption in the 1950s due to having an already largely completed and signed highway system; placing exit number signage across the state was deemed too expensive. To control costs, California began to incorporate exit numbers on its freeways in 2002—Interstate, US, and state routes alike. [[California Department of Transportation|Caltrans]] commonly installs exit number signage only when a freeway or interchange is built, reconstructed, retrofitted, or repaired, and it is usually tacked onto the top-right corner of an already existing sign. Newer signs along the freeways follow this practice as well. Most exits along California's Interstates now have exit number signage, particularly in rural areas. California, however, still does not use mileposts, although a few exist for experiments or for special purposes.<ref>{{cite web |first = Daniel P. |last = Faigin |date = December 29, 2015 |url = http://www.cahighways.org/num-postmiles.html |work = California Highways |title = Numbering Conventions: Post Miles |access-date = March 15, 2017 |archive-url = https://web.archive.org/web/20170131190248/http://www.cahighways.org/num-postmiles.html |archive-date = January 31, 2017 |url-status = live }}{{self-published source|date=March 2017}}</ref>{{self-published inline|certain=y|date=March 2017}} 

In 2010–2011, the [[Illinois State Toll Highway Authority]] posted all new mile markers to be uniform with the rest of the state on I‑90 (Jane Addams Memorial/Northwest Tollway) and the I‑94 section of the Tri‑State Tollway, which previously had matched the I‑294 section starting in the south at I‑80/I‑94/IL Route 394. This also applied to the tolled portion of the Ronald Reagan Tollway (I-88). The tollway also added exit number tabs to the exits.{{citation needed|date=December 2010}}

Exit numbers correspond to Interstate mileage markers in most states. On [[Interstate 19|I‑19]] in [[Arizona]], however, length is measured in kilometers instead of miles because, at the time of construction, [[Metrication in the United States|a push for the United States to change]] to a [[metric system]] of measurement had gained enough traction that it was mistakenly assumed that all highway measurements would eventually be changed to metric (and some distance signs retain metric distances);<ref>{{cite web |last1 = Zhang |first1 = Sarah |date = October 7, 2014 |title = An Arizona Highway Has Used the Metric System Since the 80s |url = https://gizmodo.com/an-arizona-highway-has-used-the-metric-system-since-the-1643536691 |website = Gizmodo |access-date = February 25, 2019 |archive-url = https://web.archive.org/web/20190225103128/https://gizmodo.com/an-arizona-highway-has-used-the-metric-system-since-the-1643536691 |archive-date = February 25, 2019 |url-status = live}}</ref> proximity to metric-using Mexico may also have been a factor, as I‑19 indirectly connects I‑10 to the [[Mexican Federal Highway]] system via surface streets in [[Nogales, Arizona|Nogales]]. Mileage count increases from west to east on most even-numbered Interstates; on odd-numbered Interstates mileage count increases from south to north.

Some highways, including the [[New York State Thruway]], use sequential exit-numbering schemes. Exits on the New York State Thruway count up from [[Yonkers, New York|Yonkers]] traveling north, and then west from Albany. I‑87 in New York State is numbered in three sections. The first section makes up the [[Major Deegan Expressway]] in [[the Bronx]], with interchanges numbered sequentially from 1 to 14. The second section of I‑87 is a part of the [[New York State Thruway]] that starts in Yonkers (exit&nbsp;1) and continues north to Albany (exit&nbsp;24); at Albany, the Thruway turns west and becomes I‑90 for exits&nbsp;25 to 61. From Albany north to the Canadian border, the exits on I‑87 are numbered sequentially from 1 to 44 along the [[Adirondack Northway]]. This often leads to confusion as there is more than one exit on I‑87 with the same number. For example, exit&nbsp;4 on Thruway section of I‑87 connects with the Cross County Parkway in Yonkers, but exit&nbsp;4 on the Northway is the exit for the Albany airport. These two exits share a number but are located {{convert|150|mi}} apart.

Many northeastern states label exit numbers sequentially, regardless of how many miles have passed between exits. States in which Interstate exits are still numbered sequentially are Connecticut, Delaware, New Hampshire, New York, and Vermont; as such, three of the main Interstate Highways that remain completely within these states ([[Interstate 87 (New York)|87]], [[Interstate 88 (New York)|88]], [[Interstate 89|89]]) have interchanges numbered sequentially along their entire routes. Maine, Massachusetts, Pennsylvania, Virginia, Georgia, and Florida followed this system for a number of years, but have since converted to mileage-based exit numbers. Georgia renumbered in 2000, while Maine did so in 2004. Massachusetts converted its exit numbers in 2021, and most recently Rhode Island in 2022.<ref>{{cite web |author = Massachusetts Department of Transportation |date = n.d. |title = Massachusetts Department of Transportation completed projects |url = https://www.mass.gov/info-details/massachusetts-department-of-transportation-completed-projects#statewide-exit-renumbering-project---2021- |publisher = Massachusetts Department of Transportation |access-date = September 20, 2022 }}</ref> The [[Pennsylvania Turnpike]] uses both mile marker numbers and sequential numbers. Mile marker numbers are used for signage, while sequential numbers are used for numbering interchanges internally. The [[New Jersey Turnpike]], including the portions that are signed as I‑95 and I‑78, also has sequential numbering, but other Interstates within New Jersey use mile markers.