Editing Interstate Highway System (section)

==Standards==
{{Main|Interstate Highway standards}}
The [[American Association of State Highway and Transportation Officials]] (AASHTO) has defined a set of standards that all new Interstates must meet unless a waiver from the [[Federal Highway Administration]] (FHWA) is obtained. One almost absolute standard is the [[controlled-access highway|controlled access]] nature of the roads. With few [[List of gaps in Interstate Highways|exceptions]], [[traffic light]]s (and cross traffic in general) are limited to [[Toll house|toll booths]] and [[ramp meter]]s (metered flow control for lane merging during [[rush hour]]).

===Speed limits===
{{Further|Speed limits in the United States|National Maximum Speed Law}}
[[File:2019-07-15 11 10 50 View south along Interstate 95 from the overpass for Maryland State Route 175 (Waterloo Road-Rouse Parkway) in Columbia, Howard County, Maryland.jpg|alt=|thumb|[[Interstate 95 in Maryland|I-95]] in [[Columbia, Maryland]], built to modern standards.]]
[[File:Interstate_5_in_the_Central_Valley.jpg|thumb|right|A rural stretch of [[Interstate 5 in California|I-5]] in California; two lanes in each direction are separated by a large grassy [[central reservation|median]] and cross-traffic is limited to [[grade separation]]s such as this overpass.]]
Being [[freeway]]s, Interstate Highways usually have the highest [[speed limit]]s in a given area. Speed limits are determined by individual states. From 1975 to 1986, the maximum speed limit on any highway in the United States was {{Convert|55|mi/h|km/h|round=5}}, in accordance with federal law.<ref name="nytimes3a">{{cite news |title = Nixon Approves Limit of 55 M.P.H. |url = http://select.nytimes.com/gst/abstract.html?res=F40610FD3F58137B93C1A9178AD85F408785F9&scp=1&sq=nixon%20approves%20limit%20of%2055&st=cse |access-date = July 27, 2008 |work = The New York Times |pages = 1, 24 |date = January 3, 1974 |url-access = subscription |archive-url = https://web.archive.org/web/20110605095932/http://select.nytimes.com/gst/abstract.html?res=F40610FD3F58137B93C1A9178AD85F408785F9&scp=1&sq=nixon%20approves%20limit%20of%2055&st=cse |archive-date= June 5, 2011 |url-status= dead}}</ref>

Typically, lower limits are established in [[Northeastern United States|Northeastern]] and coastal states, while higher speed limits are established in inland states west of the [[Mississippi River]].<ref name="mit">{{cite web |url = https://www.mit.edu/~jfc/laws.html |title = State traffic and speed laws |date = October 11, 2007 |access-date = January 10, 2008 |publisher = Massachusetts Institute of Technology |last = Carr |first = John |archive-url = https://web.archive.org/web/20130807221607/http://www.mit.edu/~jfc/laws.html |archive-date = August 7, 2013 |url-status = live }}</ref> For example, the maximum speed limit is {{convert|75|mph|km/h|round=5|abbr=on}} in northern Maine, varies between {{convert|50|and|70|mph|km/h|round=5|abbr=on}}<ref>{{cite news |first = Paul |last = Koenig |date = May 27, 2014 |title = Speed Limit on Much of I-295 Rises to 70&nbsp;MPH |url = http://www.pressherald.com/2014/05/27/speed_limt_on_much_of_maine_turnpike__i-295_ro_rise_to_70_mph/ |work = [[Portland Press Herald]] |access-date = July 22, 2014 |archive-url = https://web.archive.org/web/20140727171449/http://www.pressherald.com/2014/05/27/speed_limt_on_much_of_maine_turnpike__i-295_ro_rise_to_70_mph/ |archive-date = July 27, 2014 |url-status = live }}</ref> from southern Maine to New Jersey, and is {{convert|50|mph|km/h|round=5|abbr=on}} in New York City and the District of Columbia.<ref name="mit" /> Currently, rural speed limits elsewhere generally range from {{convert|65|to|80|mph|km/h|round=5}}. Several portions of various highways such as [[Interstate 10 in Texas|I-10]] and [[Interstate 20 in Texas|I-20]] in rural western Texas, [[Interstate 80 in Nevada|I-80]] in Nevada between Fernley and Winnemucca (except around Lovelock) and portions of [[Interstate 15 in Utah|I-15]], [[Interstate 70 in Utah|I-70]], [[Interstate 80 in Utah|I-80]], and [[Interstate 84 in Utah|I-84]] in Utah have a speed limit of {{convert|80|mph|km/h|round=5|abbr=on}}. Other Interstates in Idaho, Montana, Oklahoma, South Dakota and Wyoming also have the same high speed limits.

In some areas, speed limits on Interstates can be significantly lower in areas where they traverse significantly hazardous areas. The maximum speed limit on [[Interstate 90 in Ohio|I-90]] is {{convert|50|mph|km/h|round=5|abbr=on}} in downtown [[Cleveland]] because of two sharp curves with a suggested limit of {{convert|35|mph|km/h|round=5|abbr=on}} in a heavily congested area; [[Interstate 70 in West Virginia|I-70]] through [[Wheeling, West Virginia]], has a maximum speed limit of {{convert|45|mph|km/h|round=5|abbr=on}} through the [[Wheeling Tunnel]] and most of downtown Wheeling; and [[Interstate 68|I-68]] has a maximum speed limit of {{convert|40|mph|km/h|round=5|abbr=on}} through [[Cumberland, Maryland]], because of multiple hazards including sharp curves and narrow lanes through the city. In some locations, low speed limits are the result of lawsuits and resident demands; after holding up the completion of [[Interstate 35E (Minnesota)|I-35E]] in [[St. Paul, Minnesota]], for nearly 30&nbsp;years in the courts, residents along the stretch of the freeway from the southern city limit to downtown successfully lobbied for a {{convert|45|mph|km/h|round=5|abbr=on}} speed limit in addition to a prohibition on any vehicle weighing more than {{convert|9,000|lbs|kg}} [[gross vehicle weight]]. [[Interstate 93|I-93]] in [[Franconia Notch State Park]] in northern New Hampshire has a speed limit of {{convert|45|mph|km/h|round=5|abbr=on}} because it is a parkway that consists of only one lane per side of the highway. On the other hand, Interstates 15, 80, 84, and 215 in Utah have speed limits as high as {{convert|70|mph|km/h|round=5|abbr=on}} within the [[Wasatch Front]], [[Cedar City, Utah|Cedar City]], and [[St. George, Utah|St. George]] areas, and [[Interstate 25 in New Mexico|I-25]] in New Mexico within the [[Santa Fe, New Mexico|Santa Fe]] and [[Las Vegas, New Mexico|Las Vegas]] areas along with [[Interstate 20 in Texas|I-20]] in Texas along Odessa and [[Midland, Texas|Midland]] and [[Interstate 29 in North Dakota|I-29]] in North Dakota along the [[Grand Forks, North Dakota|Grand Forks]] area have higher speed limits of {{convert|75|mph|km/h|round=5|abbr=on}}.

===Other uses===
As one of the components of the [[National Highway System (United States)|National Highway System]], Interstate Highways improve the mobility of military troops to and from airports, seaports, rail terminals, and other military bases. Interstate Highways also connect to other roads that are a part of the [[Strategic Highway Network]], a system of roads identified as critical to the [[US Department of Defense]].<ref name="slater_1996">{{cite magazine |url = https://highways.dot.gov/public-roads/spring-1996/national-highway-system-commitment-americas-future |title = The National Highway System: A Commitment to America's Future |magazine = Public Roads |last = Slater |first = Rodney E. |date = Spring 1996 |volume = 59 |issue = 4 |access-date = January 10, 2008 |issn = 0033-3735 |archive-url = https://web.archive.org/web/20141216112008/http://www.fhwa.dot.gov/publications/publicroads/96spring/p96sp2.cfm |archive-date = December 16, 2014 |url-status = live }}</ref>

The system has also been used to facilitate evacuations in the face of hurricanes and other natural disasters. An option for maximizing traffic throughput on a highway is to reverse the flow of traffic on one side of a divider so that all lanes become outbound lanes. This procedure, known as [[contraflow lane reversal]], has been employed several times for hurricane evacuations. After public outcry regarding the inefficiency of evacuating from southern Louisiana prior to [[Hurricane Georges]]' landfall in September 1998, government officials looked towards contraflow to improve evacuation times. In [[Savannah, Georgia]], and [[Charleston, South Carolina]], in 1999, lanes of [[Interstate 16 in Georgia|I-16]] and [[Interstate 26 in South Carolina|I-26]] were used in a contraflow configuration in anticipation of [[Hurricane Floyd]] with mixed results.<ref name="onewayout">{{cite magazine |url = http://www.asce.org/files/pdf/hurricane/Evacuation_and_Shelters/One_Way_Out~Contraflow_Freeway_Operation_for_Hurricane_Evacuation.pdf |title = "One-Way-Out": Contraflow Freeway Operation for Hurricane Evacuation |last = Wolshon |first = Brian |magazine = Natural Hazards Review |volume = 2 |issue = 3 |pages = 105–112 |date = August 2001 |access-date = January 10, 2008 |archive-url = https://web.archive.org/web/20081006200038/http://www.asce.org/files/pdf/hurricane/Evacuation_and_Shelters/One_Way_Out~Contraflow_Freeway_Operation_for_Hurricane_Evacuation.pdf |archive-date = October 6, 2008 |doi = 10.1061/(ASCE)1527-6988(2001)2:3(105) }}</ref>

In 2004, contraflow was employed ahead of [[Hurricane Charley]] in the [[Tampa, Florida]] area and on the [[Gulf Coast of the United States|Gulf Coast]] before the landfall of [[Hurricane Ivan]];<ref name="contraflow_ivan">{{cite web |url = http://www.floridaits.com/PDFs/TWO60-Contraflow/060330-Experiences-V2.pdf |title = Contraflow Implementation Experiences in the Southern Coastal States |publisher = [[Florida Department of Transportation]] |access-date = September 27, 2007 |archive-url = https://web.archive.org/web/20071025045623/http://www.floridaits.com/PDFs/TWO60-Contraflow/060330-Experiences-V2.pdf |archive-date = October 25, 2007 |first = Tahira |last = Faquir |url-status = usurped |date = March 30, 2006 }}</ref> however, evacuation times there were no better than previous evacuation operations. Engineers began to apply lessons learned from the analysis of prior contraflow operations, including limiting exits, removing troopers (to keep traffic flowing instead of having drivers stop for directions), and improving the dissemination of public information. As a result, the 2005 evacuation of New Orleans, Louisiana, prior to [[Hurricane Katrina]] ran much more smoothly.<ref name="roadsandbridges_contraflow">{{cite web |url = https://www.roadsbridges.com/contra-productive |work = Roads & Bridges |date = December 2006b |access-date = January 10, 2008 |last = McNichol |first = Dan |title = Contra Productive |archive-url = https://web.archive.org/web/20110715191558/http://www.roadsbridges.com/popup_app/index.cfm?fuseaction=showArticle&appDirectory=rb&articleID=7519&forPrint=yes |archive-date = July 15, 2011 }}</ref>

According to [[urban legend]], early regulations required that one out of every five miles of the Interstate Highway System must be built straight and flat, so as to be usable by aircraft during times of war. There is no evidence of this rule being included in any Interstate legislation.<ref>{{cite web |first = Barbara |last = Mikkelson |date = April 1, 2011 |url = http://www.snopes.com/autos/law/airstrip.asp |title = Interstate Highways as Airstrips |publisher = Snopes |access-date = March 15, 2017 |archive-url = https://wayback.archive-it.org/all/20051201041356/http://www.snopes.com/autos/law/airstrip.asp |archive-date = December 1, 2005 |url-status = live }}</ref><ref>{{cite magazine |url = https://highways.dot.gov/public-roads/mayjune-2000/one-mile-five-debunking-myth |title = One Mile in Five: Debunking the Myth |last = Weingroff |first = Richard F. |date = May–June 2000 |magazine = Public Roads |volume = 63 |issue = 6 |access-date = December 14, 2010 |issn = 0033-3735 |archive-url = https://web.archive.org/web/20101212070757/http://www.fhwa.dot.gov/publications/publicroads/00mayjun/onemileinfive.cfm |archive-date = December 12, 2010 |url-status = live }}</ref> It is also [[List of common misconceptions|commonly believed]] the Interstate Highway System was built for the sole purpose of evacuating cities in the event of [[nuclear warfare]]. While military motivations were present, the primary motivations were civilian.<ref>{{cite web |author = Federal Highway Administration |date= June 30, 2023 |title = Interstate Highway System: The Myths |url = https://highways.dot.gov/highway-history/interstate-system/50th-anniversary/interstate-highway-system-myths#question2 |url-status = live |archive-url = https://web.archive.org/web/20240429041854/https://highways.dot.gov/highway-history/interstate-system/50th-anniversary/interstate-highway-system-myths#question2 |archive-date = April 29, 2024 |access-date = June 24, 2024 |publisher = Federal Highway Administration }}</ref><ref>{{cite news |last = Laskow |first = Sarah |date = August 24, 2015 |title = Eisenhower and History's Worst Cross-Country Road Trip |url = https://slate.com/human-interest/2015/08/in-1919-eisenhower-took-a-disastrous-road-trip-that-led-to-his-support-of-the-modern-paved-highway.html |access-date = June 24, 2024 |work = [[Slate (magazine)|Slate]] }}</ref>