Interstate Highway System 43950 226084905 2008-07-16T19:31:16Z LiberalFascist 819997 /* Extremes */ updating most travelled data to 2006 U.S. Government Data [[Image:Map of current Interstates.svg|right|thumb|Interstate Highways in the 48 contiguous states. Purple routes are currently built and open freeways, blue are currently open spur routes, and green indicates proposed routes, future roads, or those currently under construction.]] [[Image:Interstate5incentralvalley.jpg|right|thumb|A rural stretch of [[Interstate 5 (California)|Interstate 5]] in [[California]], with two lanes in each direction separated by a large grassy [[median (highway)|median]], and with cross-traffic limited to overpasses and underpasses.]] The '''Dwight D. Eisenhower National System of Interstate and Defense Highways''', commonly called the '''Interstate Highway System''' (or simply, the '''Interstate System'''), is a network of [[highways]] (also called freeways or expressways) in the [[United States]] that is named for [[Dwight D. Eisenhower|the president]] who championed its creation. The Interstate Highway System is a separate system within the larger [[National Highway System (United States)|National Highway System]]. The entire system, as of 2004, had a total length of 46,837 miles (75,376&nbsp;km),<ref name="mndot_celebrates">{{cite web|url=http://www.dot.state.mn.us/interstate50/50facts.html|title=Mn/DOT celebrates Interstate Highway System's 50th anniversary|accessdate=2007-09-27}}</ref> making it both the largest highway system in the world and the largest [[public works]] project in history.<ref>{{cite web |url=http://www.tfhrc.gov/pubrds/06jan/01.htm|title=The Year of the Interstate|accessdate=2008-04-29}}</ref> While Interstate highways usually receive substantial federal funding and comply with federal standards, they are owned, built, and operated by the states or toll authorities. The original [[Woodrow Wilson Bridge]], for example, part of [[Interstate 95]] and [[Interstate 495 (Capital Beltway)|Interstate 495]], was maintained by the federal government; its new span is now jointly owned and maintained by the State of Maryland and the Commonwealth of Virginia.<ref>{{cite web |url=http://www.wilsonbridge.com/financial%20plan/august%202001%20initial%20financial%20plan%20-%20attachment%20v.pdf|title=Attachment V, Ownership and Maintenance Agreement for the Wilson Bridge, Woodrow Wilson Bridge Initial Financial Plan|work=Woodrow Wilson Bridge Project|accessdate=2007-08-02}}</ref> The system serves nearly all major U.S. cities, with many Interstates passing through [[downtown]] areas. The distribution of virtually all goods and services involves Interstate highways at some point.<ref name=caltrans_50>{{cite web |url=http://www.dot.ca.gov/interstate/ |title=The Interstate Highway System Turns 50 |date=2006 |accessdate=2008-01-10 |author=Caltrans}}</ref> Residents of American cities commonly use urban Interstates to travel to their places of work. The vast majority of long-distance travel, whether for vacation or business, uses the national road network;<ref>{{cite web|work=Bureau of Transportation Statistics |url=http://www.bts.gov/publications/national_transportation_statistics/2002/html/table_01_36.html |title=Table 1-36: Long-Distance Travel in the United States by Selected Trip Characteristics |date=1995 |accessdate=2006-12-21}}</ref> of these trips, about one-third (by the total number of miles driven in the country in 2003) utilize the Interstate system.<ref>{{cite web|work=Federal Highway Administration|url=http://www.fhwa.dot.gov/policy/ohim/hs03/htm/vm1.htm|title=Annual Vehicle Distance Traveled in Miles and Related Data|date=2003|accessdate=2006-12-21}}</ref> ==History== [[Image:Eisenhower Interstate System.svg|thumb|right|150px|Commemorative sign introduced in 1993. Though the system was established during Dwight D. Eisenhower's presidency, the five stars commemorate his rank as [[General of the Army (USA)|General of the Army]] during [[World War II]].]] The Interstate Highway System was authorized by the [[Federal-Aid Highway Act of 1956]], popularly known as the National Interstate and Defense Highways Act of 1956, on [[June 29]]. It had been lobbied for by major U.S. [[automobile]] manufacturers and championed by President [[Dwight D. Eisenhower]], who was influenced by his experiences in 1919 as a young soldier crossing the country (following the route of the [[Lincoln Highway]]) and his appreciation of the [[Germany|German]] [[autobahn]] network as a necessary component of a national defense system. <ref> {{Citation | title=On the Road | first1=Henry | last1=Petroski | journal=American Scientist | volume=94 | issue=5 | year=2006 | pages=pp. 396-399}} </ref> In addition to facilitating private and commercial transportation, it would provide key ground transport routes for military supplies and troop deployments in an emergency. Initial federal planning for a nationwide highway system began in 1921 when the [[Bureau of Public Roads]] asked the [[United States Army|Army]] to provide a list of roads it considered necessary for national defense, resulting in the [[Pershing Map]].<ref name="mcnichol">McNichol, Dan. ''The Roads that Built America: The Incredible Story of the U.S. Interstate System''. New York: Sterling Publishing Co., Inc., 2006. ISBN 1-4027-3468-9</ref> Later that decade, highways such as the [[Parkways in New York State|New York parkway system]] had been built as part of local or state highway systems. As automobile traffic increased, planners saw a need for such an interconnected national system to supplement the existing, largely non-freeway, [[United States Numbered Highway]] system. By the late 1930s, planning had expanded to a system of new superhighways. In 1938, President [[Franklin D. Roosevelt]] gave BPR chief Thomas MacDonald a hand-drawn map of the U.S. marked with eight superhighway corridors for study.<ref name="mcnichol"/> The publication ''[[General location of national system of interstate highways]]'' maps out what became the Interstate System, and is informally known as the ''Yellow Book''.<ref>{{cite web |url=http://etext.virginia.edu/journals/EH/EH38/Norton.html |title=Fighting Traffic: U.S. Transportation Policy and Urban Congestion, 1955-1970 |author=Norton, Peter |date=1996 |accessdate=2008-01-17 |publisher=Essays in History (Corcoran Department of History at the University of Virginia)}}</ref> Although construction on the Interstate Highway System continues, [[Interstate 70 in Colorado|I-70]] through [[Glenwood Canyon]], completed in 1992, is often cited as the completion of the system.<ref name=funfacts>{{cite web |url=http://www.dot.state.co.us/50anniversary/funfacts.cfm |title = CDOT Fun Facts |accessdate = 2008-02-15 |publisher = [[Colorado Department of Transportation]]}}</ref><ref name=12yearslater>{{cite web |url = http://www.tfhrc.gov/pubrds/04mar/04.htm |title = Glenwood Canyon 12 Years Later |author = Karen Stufflebeam Row, Eva LaDow, and Steve Moler |publisher = [[United States Department of Transportation]] - [[Federal Highway Administration]]}}</ref> The initial cost estimate for the system was $25 billion over 12 years; it ended up costing $114 billion (adjusted for inflation, $425 billion in 2006 dollars<ref>{{cite news|publisher=[[USA TODAY]]|last=Neuharth|first=Al|date=[[2006-06-23]]|title=Traveling interstates is our sixth freedom}}</ref>) and taking 35 years to complete.<ref name="mndot50">{{cite web |url=http://www.dot.state.mn.us/interstate50/50facts.html |title=Mn/DOT celebrates Interstate Highway System's 50th anniversary |date=2006 |accessdate=2008-01-17 |author=Minnesota Department of Transportation}}</ref> Due to the cancellation of the [[Somerset Freeway]], [[Interstate 95 in New Jersey|Interstate 95]] is discontinuous in [[New Jersey]]. When the [[Pennsylvania Turnpike/Interstate 95 Interchange Project]] concludes in or around 2009{{update after|2009|1|1}}, the last section of the original plan will be completed.<ref name=PA>{{cite web |url = http://www.paturnpikei95.com/pdf/DACMeeting050914.pdf |author = Pennsylvania Turnpike Commission |title = I-95/I-276 Interchange Project Meeting Design Management Summary - DRAFT: Design Advisory Committee Meeting #2}}</ref> === First Interstate highway === Three different states have laid claim to the title of first Interstate highway. Missouri claims that the first three contracts under the new program were signed in Missouri on [[August 2]], [[1956]]. The first contract signed was for U.S.&nbsp;66 (now [[Interstate 44|I-44]]). On [[August 13]], [[1956]], Missouri awarded the first contract based on new Interstate highway funding.<ref name="weingroff">{{cite web |url=http://www.fhwa.dot.gov/infrastructure/rw96h.htm |title=Three States Claim First Interstate Highway |author=Weingroff, Richard F. |date=2005-05-07 |accessdate=2008-02-16 |publisher=Federal Highway Administration}}</ref> Kansas claims that it was the first to start paving after the act was signed. Preliminary construction had taken place before the act was signed, and paving started [[September 26]], [[1956]]. The state marked its portion of I-70 as the "first project in the United States completed under the provisions of the new Federal-Aid Highway Act of 1956." <ref name="weingroff" /> According to information liaison specialist Richard Weingroff, the [[Pennsylvania Turnpike]] could also be considered one of the first Interstate highways. On [[October 1]], [[1940]], {{convert|260|km|mi|0}} of the highway opened between [[Irwin, Pennsylvania|Irwin]] and [[Carlisle, Pennsylvania|Carlisle]]. The state of Pennsylvania refers to the turnpike as "The Granddaddy of the Pikes."<ref name="weingroff" /> ==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]] 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 booth]]s and [[ramp meter]]s (metered flow control for lane merging during [[rush hour]]). ===Speed limits=== {{see|Speed limits in the United States}} Interstate highways usually have the highest [[speed limit]]s in a given area. Speed limits are determined by individual states. Rural speed limits generally range from 65 to 75 miles per hour (105&ndash;120 km/h), although remote portions of [[Interstate 10|I-10]] and [[Interstate 20|I-20]] in rural western Texas have speed limits of {{convert|80|mph|km/h|sigfig=2|abbr=on}}. Typically, lower limits are located in the northeastern states, while higher speed limits are located in the southern and western states.<ref name="mit">{{cite web |url=http://www.mit.edu/~jfc/laws.html |title=State traffic and speed laws |date=2007-10-11 |accessdate=2008-01-10 |author=Carr, John}}</ref> === Other uses === As one of the components of the 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]] (abbreviated STRAHNET), a system of roads identified as critical to the [[U.S. Department of Defense]].<ref name="slater_1996">{{cite web |url=http://www.tfhrc.gov/pubrds/spring96/p96sp2.htm |title=The National Highway System: A Commitment to America's Future |author=Slater, Rodney E. |date=Spring 1996 |accessdate=2008-01-10}}</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|contraflow]], 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&nbsp;1998, government officials looked towards contraflow to improve evacuation times. In [[Savannah, Georgia]] and [[Charleston, South Carolina]] in 1999, lanes of Interstates [[Interstate 16|16]] and [[Interstate 26|26]] were used in a [[contraflow]] configuration in anticipation of [[Hurricane Floyd]], with mixed results.<ref name="onewayout">{{cite web |url=http://www.google.com/url?sa=t&ct=res&cd=3&url=http%3A%2F%2Fwww.asce.org%2Ffiles%2Fpdf%2Fhurricane%2FEvacuation_and_Shelters%2FOne_Way_Out~Contraflow_Freeway_Operation_for_Hurricane_Evacuation.pdf&ei=p2eGR87TB5ngiAHs1cTzBA&usg=AFQjCNHdMFt9MMBYGRtxh6dx3hucEK6hTw&sig2=8GG0G3JHXyG7rIsspWiXbQ |title="One-Way-Out": Contraflow Freeway Operation for Hurricane Evacuation |author=Wolshon, Brian, P.E. |date=August 2001 |accessdate=2008-01-10}}</ref> In 2004, contraflow was employed ahead of [[Hurricane Charley]] in the [[Tampa, Florida]] area and on the [[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|author=Florida Department of Transportation|accessdate=2007-09-27}}</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 (so as to keep traffic flowing, instead of having drivers stop for directions), and improving the dissemination of public information. As a result, the 2005 evacuations of [[New Orleans, Louisiana]], and [[Houston, Texas]], prior to hurricanes [[Hurricane Katrina|Katrina]] and [[Hurricane Rita|Rita]] ran far more smoothly.<ref name=roadsandbridges_contraflow>{{cite web |url=http://www.roadsbridges.com/popup_app/index.cfm?fuseaction=showArticle&appDirectory=rb&articleID=7519&forPrint=yes |publisher=Roads & Bridges |date=December 2006 |accessdate=2008-01-10 |author=McNichol, Dan |title=Contra Productive}}</ref> A widespread [[urban legend]] states 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. Contrary to popular lore, Interstate highways are not designed to serve as airstrips. <ref>{{Citation |url=http://www.snopes.com/autos/law/airstrip.asp |title=Landing of Hope and Glory |publisher=snopes.com |accessdate=[[2007-12-30]]}}</ref><ref>{{cite web|url=http://www.tfhrc.gov/pubrds/mayjun00/onemileinfive.htm|title=ONE MILE IN FIVE: Debunking the Myth|last=Weingroff|first=Richard F.|date=May/June 2000|work=Federal Highway Administration|accessdate=2006-06-29}}</ref> ==Terminology== While the name implies that Interstate highways cross state lines, many do not (for details see [[List of intrastate Interstates]]). Rather, they are ''funded'' federally with money shared ''among the states''. There are Interstate highways in [[Hawaii]], funded in the same way as in the other states, but entirely within the populous island of [[Oahu]]. They have the designation of H-<math>x</math> and connect military bases, though they are open to public use. Both [[Alaska]] and [[Puerto Rico]] have public roads that receive funding from the Interstate program, although these routes are not signed as Interstate highways (except on paper). These roads are neither planned for, nor built to, official Interstate highway standards. ===Primary routes=== {{seealso|List of Interstate Highways|List of intrastate Interstate Highways}} Interstate highways are typically known as '''Interstate XX''' or '''I-XX''', where "XX" is the one- or two-digit route number; sometimes '''Interstate Highway XX''' ('''IH&nbsp;XX''') or '''Interstate Route XX''' ('''IR&nbsp;XX''') is used. In some areas, the more generic '''Route XX''' or '''Highway XX''' is used, or in the case of Western New York, Southern California, Southern Nevada, and Honolulu, '''The XX'''.{{Fact|date=March 2008}} The numbering scheme for the Interstate Highway System (as well as the [[U.S. Highway System]]) was developed in 1957 by the [[American Association of State Highway and Transportation Officials]] (AASHTO). The association's latest numbering policy is unchanged from policy dated to [[August 10]], [[1973]].<ref name="aashto_ho2">{{cite web |url=http://cms.transportation.org/sites/route/docs/HO2_Policy_Retention_HO1.pdf |title=Establishment of a Marking System of the Routes Comprising the National System of Interstate and Defense Highways |author=AASHTO |date=January 2000 |accessdate=2008-01-23}}</ref> Within the continental United States, primary Interstates (also called main line Interstates or two-digit Interstates) are assigned numbers less than 100. AASHTO policy discourages Interstate and U.S. highways having the same number within the same state, although there are a few exceptions.<ref name="aashto_ho2" /> Within this category, east–west highways are assigned even numbers, and north–south highways are assigned odd numbers. Odd route numbers increase from west to east, and even-numbered routes increase from south to north, though there are exceptions to both principles in several locations. Numbers [[Division (mathematics)|divisible]] by 5 are intended to be major arteries among the primary routes, carrying traffic long distances.<ref name="mcnichol" /><ref name="rambler_20050118">{{cite web |url=http://www.fhwa.dot.gov/infrastructure/i76.htm |title=Ask the Rambler: Was I-76 Numbered to Honor Philadelphia for Independence Day, 1776? |author=The Rambler |publisher=Federal Highway Administration |date=2005-01-18 |accessdate=2008-01-17}}</ref> Major north–south arterial Interstates increase in number from [[Interstate 5|I-5]] between [[Canada]] and [[Mexico]] along the west coast to [[Interstate 95|I-95]] between [[Miami, Florida|Miami]] and [[Canada]] along the east coast. Major east–west arterial Interstates increase in number from [[Interstate 10|I-10]] between [[Santa Monica, California]] and [[Jacksonville, Florida]] to [[Interstate 90|I-90]] between [[Seattle, Washington|Seattle]] and [[Boston, Massachusetts|Boston]]. Two-digit Interstates in [[Hawaii]], as well as the "paper" Interstates of [[Alaska]] and [[Puerto Rico]], are numbered sequentially in order of funding, without regard to the rules on odd and even numbers. Several two-digit numbers are shared between two roads at opposite ends of the country. Some of these were the result of a change in the numbering system as a result of the new policy adopted in 1973. Previously, letter-suffixed numbers were used for long spurs off primary routes; for example, western [[Interstate 84 (west)|I-84]] was I-80N, as it went north from [[Interstate 80|I-80]]. The new policy stated that "No new divided numbers (such as [[Interstate 35W|I-35W]] and [[Interstate 35E|I-35E]], etc.) shall be adopted." The new policy also stated recommended that existing divided numbers be eliminated as quickly as possible; however, I-35W and I-35E still exist in [[Minnesota]] and [[Texas]].<ref name="aashto_ho2" /> AASHTO policy allows dual numbering so as to provide continuity between major control points.<ref name="aashto_ho2" /> This is usually referred to as a ''[[concurrency (road)|concurrency]]'' or ''overlap''. For example, [[Interstate 75|I-75]] from [[Chattanooga, Tennessee]] to [[Macon, Georgia]] and [[Interstate 85|I-85]] from [[Greenville, South Carolina]] to [[Montgomery, Alabama]] share the same roadway (the [[Downtown Connector]]) in [[Atlanta, Georgia|Atlanta]]. As a result, this section of Interstate Highway is labeled both I-75 and I-85. Concurrencies between Interstate and U.S. Route numbers are also allowed per AASHTO policy, so long as the length of the concurrency is "reasonable".<ref name="aashto_ho2" /> The concurrency policy may lead to confusion when two routes on the same roadway are marked in opposite directions. This is called a [[wrong-way concurrency]]. ===Auxiliary Interstates=== {{seealso|List of auxiliary Interstate Highways}} [[Image:FHWA Auxiliary Route Numbering Diagram.svg|thumbnail|500px|Examples of the auxiliary Interstate highway numbering system]] Auxiliary Interstate highways are circumferential, radial, or spur highways that principally serve urban areas. These types of interstate highways are given three-digit route numbers, which consist of a single digit prefixed to the two-digit number of a nearby primary interstate highway. Spur routes deviate from its parent and do not return, with a few exceptions; these are given an odd first digit. Circumferential and radial loop routes return to interstate highways, and are given an even first digit. Due to the large number of these routes, auxiliary route numbers may be repeated in different states along the mainline.<ref name="fhwa_route_log">{{cite web |url=http://www.fhwa.dot.gov/reports/routefinder/index.cfm |author=Federal Highway Administration |date=2007-03-22 |accessdate=2008-01-23 |title=FHWA Route Log and Finder List}}</ref> Some auxiliary highways do not follow these guidelines, however. See [[List of auxiliary Interstate Highways]] for these examples. In the example to the right, City A has an even-numbered circumferential highway. City B has an even-numbered circumferential beltway and an odd-numbered spur. City C has an even-numbered circumferential highway and an odd numbered spur. Because cities A, B and C are in the same state, each auxiliary route carries a distinct three-digit route number.<ref name="fhwa_route_log" /> Unlike primary Interstates, three-digit Interstates are signed as either east/west or north/south, depending on the general orientation of the route, without regard to the route number. For some looped Interstate routes, [[Inner/Outer labeling|Inner and Outer banners]] are used as a directional labeling system as opposed to compass directions. ===Business routes=== AASHTO defines a category of special routes separate from primary and auxiliary interstate designations. These routes do not have to comply to Interstate construction standards, but are routes that may be identified and approved by the association. The same route marking policy applies to both U.S. Numbered Highways and Interstate Highways; however, [[business route]] designations are sometimes used for Interstate Highways.<ref name="aashto_ho1">{{cite web |url=http://cms.transportation.org/sites/route/docs/HO1_Policy_Establ_Develop_USRN.pdf |title=Establishment and Development of United States Numbered Highways |date=January 2000 |accessdate=2008-01-23 |author=AASHTO}}</ref> Known as [[Business Loop]]s and [[Business Spur]]s, these routes that principally travel through the corporate limits of a city, passing through the [[central business district]] of the city. Business routes are used when the regular route is directed around the city.<ref name="aashto_ho1" /> ==Financing== [[Image:Freewayslc.jpg|thumb|right|[[I-15]] near Downtown [[Salt Lake City]]. Five lanes in each direction with three-lane feeders on each side]] Virtually 100 percent of the construction and maintenance costs are funded through [[user fee]]s, primarily [[fuel tax]]es, collected by states and the federal government, and tolls collected on [[toll road]]s and bridges.{{Fact|date=May 2008}} (The claim that only 56 percent of costs are funded by user fees is based on the misinterpretation of a table that applies to all highways, roads, and streets, not just the Interstate Highways.{{Fact|date=May 2008}}) In the eastern United States, large sections of some Interstate highways planned or built prior to 1956 are operated as toll roads. As American suburbs have expanded, the costs incurred in maintaining freeway infrastructure have also grown, leaving little in the way of funds for new Interstate construction.<ref>Field, David. "On 40th birthday, interstates face expensive midlife crisis." ''Insight on the News'', [[29 July]] [[1996]], 40-42.</ref> This has led to the proliferation of toll roads (turnpikes) as the new method of building limited-access highways in suburban areas. Also, some Interstates are being privately maintained (e.g., VMS maintains I-35 in Texas)<ref name="vmsom">{{cite web |url=http://www.vmsom.com/projectsoverviewbytype.shtm#Interstates |title=Projects by Type |accessdate=2008-01-10 |author=VMS, Inc.}}</ref> to meet rising costs of maintenance and allow state departments of transportation to focus on serving the fastest growing regions in their respective states. It is possible that parts of the system will have to be tolled in the future to meet maintenance and expansion demands, as has been done with adding toll HOV/[[HOT lanes]] in certain cities such as [[San Diego, California|San Diego]], [[Salt Lake City, Utah|Salt Lake City]], [[Minneapolis, Minnesota|Minneapolis]], [[Houston, Texas|Houston]], [[Dallas, Texas|Dallas]], [[Atlanta, Georgia|Atlanta]]<ref name="cobbrides">{{cite web|url=http://www.cobbrides.com/pdfs/1st%20toll%20project%20proposed%20for%20I.pdf|title=1st toll project proposed for I-20 east. Plan would add lanes outside I-285|author=Ariel Hart|publisher=Atlanta Journal-Constitution|accessdate=2007-09-27}}</ref><ref name="atlanta_hov_future">{{cite web|url=http://www.dot.state.ga.us/preconstruction/consultantdesign/design/Future%20of%20HOV%20in%20Atlanta.pdf|title=Future of HOV in Atlanta|author=Darryl D. VanMeter|accessdate=2007-09-27}}</ref> and [[Washington, D.C.]] ===Local maintenance=== A few Interstates are maintained by local authorities: *[[Baltimore, Maryland]]: [[Interstate 70]] and [[Interstate 83]] in the city limits<ref>{{PDFlink|[http://www.sha.state.md.us/SHAServices/trafficReports/mileage.pdf Maryland's Interstate System]|14.8&nbsp;[[Kibibyte|KiB]]<!-- application/pdf, 15187 bytes -->}}</ref> *[[New York City]]: Small portions of [[Interstate 278]]<ref>[http://www.dot.state.ny.us/reg/r11/r11glance/page2.html New York State Department of Transportation - Region 11 (New York City) Built and Unbuilt Arterial System]</ref> *[[Washington, D.C.]]: As the city and District are identical, the District maintains the portions of [[Interstate 66]], [[Interstate 295 (District of Columbia)|Interstate 295]], [[Interstate 395 (District of Columbia)|Interstate 395]] and [[Interstate 695 (District of Columbia)|Interstate 695]] inside the city. *[[Las Vegas, Nevada|Las Vegas]]: Much of [[Interstate 215 (Nevada)|Interstate 215]] is managed by [[Clark County, Nevada]]'s public works department. Only about four miles (6 km) of the freeway were turned over to the [[Nevada]] Department of Transportation after the road was completed. ===Chargeable and non-chargeable Interstate routes=== Interstate highways financed with federal funds are known as "chargeable" Interstate routes, and are considered part of the {{convert|42000|mi|km|sing=on}} network of highways. Federal laws<ref>{{usc|23|103|4}}</ref> allow highways funded similarly to state and US highways to be signed as Interstates, if they meet the Interstate highway standards and are logical additions or connections to the System.<ref>[http://www.cahighways.org/itypes.html California Highways: Interstate Highway Types and the History of California's Interstates]</ref> Called "non-chargeable" Interstate routes, these additions fall under two categories: routes that already meet Interstate standards, and routes not yet upgraded to Interstate standards. Only routes that meet Interstate standards may be signed as Interstates once their proposed number is approved. ==Signage== The majority of Interstates have [[exit number]]s. All [[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). However, there are 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; at the time, placing exit number signage across the state was deemed too expensive. Since 2002, however, California has begun to incorporate exit numbers on all its freeways - Interstate, U.S., and state routes alike. To mitigate costs, a common occurrence is for [[California Department of Transportation|Caltrans]] to install exit number signage only when a freeway or interchange is built, reconstructed, retrofitted, or repaired. The majority of the exits along California's Interstates now have exit number signage, particularly in rural areas.{{Fact|date=February 2008}} In most states, the exit numbers correspond to the mileage markers on the Interstates. However, on [[Interstate 19|I-19]] in [[Arizona]], length is measured in kilometers instead of miles, in part because it runs south to the Mexican border. On most even-numbered Interstates, mileage count increases from west to east; on odd-numbered Interstates, mileage count increases from south to north. Some tollways, including the [[New York State Thruway]] and [[Jane Addams Memorial Tollway]], use radial exit numbering schemes. Exits on the New York State Thruway count up from [[Yonkers, New York|Yonkers]] traveling north, and then west from Albany. On the Jane Addams Memorial Tollway, mileage markers count up from [[Chicago-O'Hare International Airport]] traveling west. 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, Massachusetts, New Hampshire, New York, Rhode Island and Vermont. Maine, Virginia, Georgia, and Florida followed this system for a number of years, but recently converted to having the exit numbers correspond to mileage markers. The [[Pennsylvania Turnpike]] uses both the mile marker number and the sequential number. The mile marker number is used for signage, while the sequential number is used for numbering interchanges internally. The New Jersey Turnpike also has sequential numbering, but other Interstates within New Jersey generally use mile markers. ===Interstate shield=== [[Image:I-95.svg|thumb|right|100px|A sample [[Interstate 95]] shield.]] Interstate Highways are signed by a number placed on a trademarked<ref name="mcnichol"/> red, white and blue [[Highway shield|sign]] as shown to the right. In the original design, the state was listed above the highway number, but in many states, this area is now left blank. The sign usually measures 36-in (91&nbsp;cm) high, and is 36-in wide for two-digit Interstates or 45-in (114&nbsp;cm) for three-digit Interstates.<ref name=ishields>[http://www.interstate-guide.com/ishields/index.html Interstate Shield Galleries]</ref> Interstate [[Business Loop|business loops]] and [[Business Spur|spurs]] use a special shield where the red and blue are replaced with green, the word BUSINESS appears instead of INTERSTATE, and the word SPUR or LOOP usually appears above the number. <ref>[http://www.interstate-guide.com/business-routes/index.html Index of Interstate Business Loops]</ref><!--We should still cite MUTCD/SHS here--> Over time the design of the Interstate shield has changed. In 1958, when the Interstate shield was introduced, the shield color was a dark navy blue and only 17-in (41&nbsp;cm) wide.<ref name=ishields /> The MUTCD standards made a few revisions to the shield in the 1961, 1972, 1988, and 2000 editions. By 2000, the shield size nearly doubled, with some Interstate shields reaching 36-in in diameter. ==Extremes== The most heavily traveled area of the Interstate Highway System is the [[Interstate 405 (California)|405 Freeway]] in [[Los Angeles, California]], with a 2006 estimate of 390,000 vehicles a day.<ref>[http://www.fhwa.dot.gov/policyinformation/tables/02.cfm Most Travelled Urban Highways Average AADT]</ref> The least traveled section is [[Interstate 95 in Maine|Interstate 95]] just north of [[Houlton, Maine]] (near the Canadian border), with 1,880 vehicles a day (2001 estimate).<ref>[http://interstate-guide.com/i-095_aadt.html Interstate 95 Annual Average Daily Traffic (AADT)]</ref> The most extreme directional points of the Interstate Highway system are: *Northernmost: The northern termini of Interstates [[Interstate 5|5]], [[Interstate 15|15]], and [[Interstate 29|29]], crossing the [[Canadian border]] at the [[49th parallel]] near, respectively, [[Blaine, Washington]]; [[Sweetgrass, Montana]]; and [[Pembina, North Dakota]]. The A-2 and A-4 highways in Alaska are farther north, but are unsigned as Interstates and are not up to normal Interstate standards. *Southernmost: A bend on [[Interstate H-1]] in the [[Kaimuki]] section of [[Honolulu, Hawaii]], less than 1/2&nbsp;mile&nbsp;(0.8&nbsp;km) before its eastern terminus (lat. 21.3 deg. N.). The southernmost point in the 48 contiguous states is the southern terminus of [[Interstate 95 in Florida|Interstate 95]] in [[Miami, Florida]] (lat. 25.8 deg. N.). *Easternmost: The northern terminus of Interstate 95 near [[Houlton, Maine]], at the border of [[New Brunswick]] in Canada (long. 67.8 deg. W.). *Westernmost: The western terminus of Interstate H-1 in [[Kapolei, Hawaii]] (long. 158.06 deg. W.). The westernmost point in the contiguous states is a curve on Interstate 5 near [[Wolf Creek, Oregon]] (long. 123.23 deg. W.). The highest point on the Interstate Highway System is at the [[Eisenhower Tunnel]] on [[Interstate 70]] in the [[Rocky Mountains]] of [[Colorado]], at the [[Continental Divide]] (elev. {{convert|11158|ft|m|0|disp=s|abbr=on}}). The lowest point on land is on [[Interstate 8]] at the [[New River (California)|New River]] near [[Seeley, California]] (elev. {{convert|-52|ft|m|0|disp=s|abbr=on}}). The lowest point under water is on [[Interstate 95]] in the [[Fort McHenry Tunnel]] under [[Baltimore Harbor]] in [[Baltimore, Maryland]] (elev. {{convert|-107|ft|m|0|disp=s|abbr=on}}). The longest Interstate highway is [[Interstate 90]], which runs {{convert|3099|mi|km|0}} between [[Boston, Massachusetts]] and [[Seattle, Washington]]. The longest north-south Interstate highway is generally cited as [[Interstate 95]]; when completed, it will run {{convert|1927|mi|km|0}} between [[Miami, Florida]] and the [[United States-Canada border|Canadian border]] (there is a gap in [[New Jersey]]). The shortest, albeit unsigned, Interstate is [[Interstate 878]], a {{convert|0.7|mi|km|sing=on}} portion of [[New York State Route 878]] adjacent to [[John F. Kennedy International Airport]] in [[Queens, New York]]. Another short unsigned Interstate is [[Interstate 110 (Texas)| Interstate 110]] near downtown [[El Paso]], with a length of {{convert|0.92|mi|km}}. The shortest signed Interstate is [[Interstate 375 (Michigan)|Interstate 375]] in downtown [[Detroit, Michigan]], at {{convert|1.06|mi|km|2}}. The shortest Interstate route segment within a state (or federal district) is I-95 in the District of Columbia which is {{convert|0.11|mi|km}} long.<ref>[http://www.fhwa.dot.gov/reports/routefinder/index.cfm Interstate Route Numbering]</ref> The section of [[Interstate 93]] in [[New Hampshire]] that runs through [[Franconia Notch State Park]] is the only instance of a two lane highway, also called a [[Super two|Super-2]] parkway, on the Interstate Highway System in the US. ==References== {{reflist|2}} ==See also== * [[Contraflow]] * [[fuel tax]] * [[Highway patrol]] * [[Non-motorized vehicle access on freeways]] * [[List of roads and highways]] * [[Mile-log]] * [[Parkway]] * [[List of major freeway systems]] * [[Adopt a Highway]] * [[International E-road network]] in Europe ==External links== {{commonscat|Interstate Highways}} * [http://www.fhwa.dot.gov/programadmin/interstate.cfm Interstate Highway information] * [http://www.fhwa.dot.gov/reports/routefinder/index.cfm FHWA Route Log and Finder List] * [http://www.tfhrc.gov/ FHWA Turner-Fairbank Highway Research Center] {{interstates}} [[Category:Interstate Highway System| ]] [[Category:History of the United States (1945–1964)]] [[Category:Dwight D. Eisenhower]] [[bg:Междущатска магистрална система]] [[da:Interstate Highway System]] [[de:Interstate Highway]] [[es:Red de Autopistas Interestatales de Estados Unidos]] [[eo:Interŝtata Ŝosea Sistemo]] [[fr:Interstate highway]] [[gl:Interstate Highway System]] [[it:Interstate Highway System]] [[nl:Interstate highway]] [[ja:州間高速道路]] [[pl:Interstate Highway System]] [[pt:Interstate Highway System]] [[ru:Система межштатных автомагистралей США]] [[simple:Interstate Highway]] [[fi:Interstate Highway System]] [[sv:Interstate Highway System]] [[ta:இடைமாநில நெடுஞ்சாலை முறை]] [[th:ระบบทางหลวงอินเตอร์สเตต]] [[yi:אינטערסטעיט הייוועי סיסטעם]] [[zh:州際公路系統]]