Interstate Highway System

"Interstate" redirects here. For the type of highway, seeControlled-access highway.For other uses, seeInterstate (disambiguation).

TheDwight D. Eisenhower National System of Interstate and Defense Highways,commonly known as theInterstate Highway System,or theEisenhower Interstate System,is a network ofcontrolled-access highwaysthat forms part of theNational Highway Systemin theUnited States.The system extends throughout thecontiguous United Statesand has routes inHawaii,Alaska,andPuerto Rico.

Dwight D. Eisenhower National System of Interstate and Defense Highways
Highway shieldsfor Interstate 80, Business Loop Interstate 80, and the Eisenhower Interstate System
Primary Interstate Highways in the 48 contiguous states.Alaska, Hawaii, and Puerto Ricoalso have Interstate Highways.
System information
Length	48,890 mi(78,680 km)
Formed	June 29, 1956(1956-06-29)
Highway names
Interstates	Interstate X (I-X)
System links
Interstate Highway System Main Auxiliary Suffixed Business Future

In the 20th century, theUnited States Congressbegan funding roadways through theFederal Aid Road Act of 1916,and started an effort to construct a national road grid with the passage of theFederal Aid Highway Act of 1921.In 1926, theUnited States Numbered Highway Systemwas established, creating the first national road numbering system for cross-country travel. The roads were funded and maintained byU.S. states,and there were few national standards for road design. United States Numbered Highways ranged from two-lane country roads to multi-lane freeways. AfterDwight D. Eisenhowerbecame president in 1953,his administrationdeveloped a proposal for an interstate highway system, eventually resulting in the enactment of theFederal-Aid Highway Act of 1956.

Unlike the earlier United States Numbered Highway System, the interstates were designed to be all freeways, with nationally unified standards for construction and signage. While some older freeways were adopted into the system, most of the routes were completely new. In dense urban areas, the choice of routing destroyed many well-established neighborhoods, often intentionally as part of a program of "urban renewal".In the two decades following the 1956 Highway Act, the construction of the freeways displaced one million people,and as a result of the manyfreeway revoltsduring this era, several planned Interstates were abandoned or re-routed to avoid urban cores.

Construction of the original Interstate Highway System was proclaimed complete in 1992, despite deviations from the original 1956 plan and severalstretches that did not fully conform with federal standards.The construction of the Interstate Highway System cost approximately $114 billion (equivalent to $618 billion in 2023). The system has continued to expand and grow as additional federal funding has provided for new routes to be added, and manyfuture Interstate Highwaysare currently either being planned or under construction.

Though heavily funded by the federal government, Interstate Highways are owned by the state in which they were built. Withfew exceptions,all Interstates must meetspecific standards,such as having controlled access, physical barriers ormedian stripsbetween lanes of oncoming traffic,breakdown lanes,avoidingat-grade intersections,notraffic lights,and complying with federaltraffic signspecifications. Interstate Highways use a numbering scheme in which primary Interstates are assigned one- or two-digit numbers, and shorter routes which branch off from longer ones are assigned three-digit numbers where the last two digits match the parent route. The Interstate Highway System is partially financed through theHighway Trust Fund,which itself is funded by a combination of a federalfuel taxand transfers from theTreasury'sgeneral fund.Though federal legislation initially banned the collection of tolls, some Interstate routes aretoll roads,either because they weregrandfathered intothe system or because subsequent legislation has allowed for tolling of Interstates in some cases.

As of 2022,about one quarter of all vehicle miles driven in the country used the Interstate Highway System,which has a total length of 48,890 miles (78,680 km).In 2022 and 2023, the number of fatalities on the Interstate Highway System amounted to more than 5,000 people annually, with nearly 5,600 fatalities in 2022.

History

Planning

The Pershing Map

FDR's hand-drawn map from 1938

The United States government's efforts to construct a national network of highways began on anad hocbasis with the passage of theFederal Aid Road Act of 1916,which provided $75 million over a five-year period formatching fundsto the states for the construction and improvement of highways.The nation's revenue needs associated withWorld War Iprevented any significant implementation of this policy, which expired in 1921.

In December 1918, E. J. Mehren, a civil engineer and the editor ofEngineering News-Record,presented his "A Suggested National Highway Policy and Plan"during a gathering of the State Highway Officials and Highway Industries Association at the Congress Hotel in Chicago.In the plan, Mehren proposed a 50,000-mile (80,000 km) system, consisting of five east–west routes and 10 north–south routes. The system would include two percent of all roads and would pass through every state at a cost of $25,000 per mile ($16,000/km), providing commercial as well as military transport benefits.

In 1919, the US Army sent an expedition across the US to determine the difficulties that military vehicles would have on a cross-country trip. Leaving fromthe Ellipsenear theWhite Houseon July 7, theMotor Transport Corps convoyneeded 62 days to drive 3,200 miles (5,100 km) on theLincoln Highwayto thePresidio of San Franciscoalong theGolden Gate.The convoy suffered many setbacks and problems on the route, such as poor-quality bridges, broken crankshafts, and engines clogged with desert sand.

Dwight Eisenhower,then a 28-year-oldbrevetlieutenant colonel,accompanied the trip "through darkest America with truck and tank," as he later described it. Some roads in the West were a "succession of dust, ruts, pits, and holes."

As the landmark 1916 law expired, new legislation was passed—theFederal Aid Highway Act of 1921(Phipps Act). This new road construction initiative once again provided for federal matching funds for road construction and improvement, $75 million allocated annually.Moreover, this new legislation for the first time sought to target these funds to the construction of a national road grid of interconnected "primary highways", setting up cooperation among the various state highway planning boards.

TheBureau of Public Roadsasked theArmyto provide a list of roads that it considered necessary for national defense.In 1922, GeneralJohn J. Pershing,former head of theAmerican Expeditionary Forcein Europe during the war, complied by submitting a detailed network of 20,000 miles (32,000 km) of interconnected primary highways—the so-calledPershing Map.

A boom in road construction followed throughout the decade of the 1920s, with such projects as theNew York parkway systemconstructed as part of a new national highway system. As automobile traffic increased, planners saw a need for such an interconnected national system to supplement the existing, largely non-freeway,United States Numbered Highwayssystem. By the late 1930s, planning had expanded to a system of new superhighways.

In 1938, PresidentFranklin D. RooseveltgaveThomas MacDonald,chief at the Bureau of Public Roads, a hand-drawn map of the United States marked with eight superhighway corridors for study.In 1939, Bureau of Public Roads Division of Information chiefHerbert S. Fairbankwrote a report calledToll Roads and Free Roads,"the first formal description of what became the Interstate Highway System" and, in 1944, the similarly themedInterregional Highways.

Federal Aid Highway Act of 1956

Main article:Federal Aid Highway Act of 1956

The Interstate Highway System gained a champion in President Dwight D. Eisenhower, who was influenced by his experiences as a young Army officer crossing the country in the 1919 Motor Transport Corps convoy that drove in part on theLincoln Highway,the first road across America. He recalled that, "The old convoy had started me thinking about good two-lane highways... the wisdom of broader ribbons across our land."Eisenhower also gained an appreciation of theReichsautobahnsystem, the first "national" implementation of modern Germany'sAutobahnnetwork, as a necessary component of a national defense system while he was serving asSupreme CommanderofAllied Forcesin Europe duringWorld War II.In 1954, Eisenhower appointed GeneralLucius D. Clayto head a committee charged with proposing an interstate highway system plan.Summing up motivations for the construction of such a system, Clay stated,

It was evident we needed better highways. We needed them for safety, to accommodate more automobiles. We needed them for defense purposes, if that should ever be necessary. And we needed them for the economy. Not just as a public works measure, but for future growth.

Clay's committee proposed a 10-year, $100 billion program ($1.13 trillion in 2023), which would build 40,000 miles (64,000 km) ofdivided highwayslinking all American cities with a population of greater than 50,000. Eisenhower initially preferred a system consisting oftoll roads,but Clay convinced Eisenhower that toll roads were not feasible outside of the highly populated coastal regions. In February 1955, Eisenhower forwarded Clay's proposal to Congress. The bill quickly won approval in the Senate, but House Democrats objected to the use of publicbondsas the means to finance construction. Eisenhower and the House Democrats agreed to instead finance the system through theHighway Trust Fund,which itself would be funded by agasolinetax.In June 1956, Eisenhower signed theFederal Aid Highway Act of 1956into law. Under the act, the federal government would pay for 90 percent of the cost of construction of Interstate Highways. Each Interstate Highway was required to be afreewaywith at least four lanes and no at-grade crossings.

The publication in 1955 of theGeneral Location of National System of Interstate Highways,informally known as theYellow Book,mapped out what became the Interstate Highway System.Assisting in the planning wasCharles Erwin Wilson,who was still head ofGeneral Motorswhen President Eisenhower selected him as Secretary of Defense in January 1953.

Construction

1955 map: The planned status of US Highways in 1965, as a result of the developing Interstate Highway System

I‑55under construction inMississippiin May 1972

1957 aerial photograph showing a recently constructed interchange on I-5 inGlendale, California

Some sections of highways that became part of the Interstate Highway System actually began construction earlier.

Three states have claimed 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 upgrading a section ofUS Route 66to what is now designatedInterstate 44.On August 13, 1956, work began onUS 40(now I-70) in St. Charles County.

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 ofI-70as the first project in the United States completed under the provisions of the new Federal-Aid Highway Act of 1956.

ThePennsylvania Turnpikecould also be considered one of the first Interstate Highways, and is nicknamed "Grandfather of the Interstate System".On October 1, 1940, 162 miles (261 km) of the highway now designated I‑70 and I‑76 opened betweenIrwinandCarlisle.TheCommonwealth of Pennsylvaniarefers to the turnpike as the Granddaddy of the Pikes, a reference toturnpikes.

Milestones in the construction of the Interstate Highway System include:

• October 17, 1974:Nebraskabecomes the first state to complete all of its mainline Interstate Highways with the dedication of its final piece ofI-80.
• October 12, 1979: The final section of the Canada to Mexico freewayInterstate 5is dedicated nearStockton, California.Representatives of the two neighboring nations attended the dedication to commemorate the first contiguous freeway connecting the North American countries.
• August 22, 1986: The final section of the coast-to-coastI-80(San Francisco, California,toTeaneck, New Jersey) is dedicated on the western edge ofSalt Lake City, Utah,making I-80 the world's first contiguous freeway to span from the Atlantic to Pacific Ocean and, at the time, the longest contiguous freeway in the world. The section spanned fromRedwood Roadto just west of theSalt Lake City International Airport.At the dedication it was noted that coincidentally this was only 50 miles (80 km) fromPromontory Summit,where a similar feat was accomplished nearly 120 years prior, the driving of thegolden spikeof the United States'First transcontinental railroad.
• August 10, 1990: The final section of coast-to-coastI-10(Santa Monica, California,toJacksonville, Florida) is dedicated, thePapago Freeway Tunnelunder downtownPhoenix, Arizona.Completion of this section was delayed due to afreeway revoltthat forced the cancellation of an originally planned elevated routing.
• September 12, 1991:I-90becomes the final coast-to-coast Interstate Highway (Seattle, WashingtontoBoston, Massachusetts) to be completed with the dedication of an elevatedviaductbypassingWallace, Idaho,which opened a week earlier.This section was delayed after residents forced the cancellation of the originally planned at-grade alignment that would have demolished much ofdowntown Wallace.The residents accomplished this feat by arranging for most of the downtown area to be declared ahistoric districtand listed on theNational Register of Historic Places;this succeeded in blocking the path of the original alignment. Two days after the dedication residents held a mock funeral celebrating the removal of the last stoplight on a transcontinental Interstate Highway.
• October 14, 1992: The original Interstate Highway System is proclaimed to be complete with the opening ofI-70throughGlenwood CanyoninColorado.This section is considered an engineering marvel with a 12-mile (19 km) span featuring 40 bridges and numerous tunnels and is one of the most expensive rural highways per mile built in the United States.

The initial cost estimate for the system was $25 billion over 12 years; it ended up costing $114 billion (equivalent to $425 billion in 2006or $618 billion in 2023) and took 35 years.

1992–present

Discontinuities

Main article:List of gaps in Interstate Highways

Commemorative sign introduced in 1993. The system was established during Dwight D. Eisenhower's presidency, and the five stars commemorate his rank asGeneral of the Armyduring World War II.

The system was proclaimed complete in 1992, but two of the original Interstates—I-95andI-70—were not continuous: both of these discontinuities were due to local opposition, which blocked efforts to build the necessary connections to fully complete the system. I-95 was made a continuous freeway in 2018,and thus I-70 remains the only original Interstate with a discontinuity.

I-95 was discontinuous in New Jersey because of the cancellation of theSomerset Freeway.This situation was remedied when the construction of thePennsylvania Turnpike/Interstate 95 Interchange Projectstarted in 2010and partially opened on September 22, 2018, which was already enough to fill the gap.

However, I-70 remains discontinuous inPennsylvania,because of the lack of a direct interchange with thePennsylvania Turnpikeat the eastern end of theconcurrencynearBreezewood.Traveling in either direction, I-70 traffic must exit the freeway and use a short stretch ofUS 30(which includes a number of roadside services) to rejoin I-70. The interchange was not originally built because of a legacy federal funding rule, since relaxed, which restricted the use of federal funds to improve roads financed with tolls.Solutions have been proposed to eliminate the discontinuity, but they have been blocked by local opposition, fearing a loss of business.

Expansions and removals

See also:Future Interstate HighwaysandFreeway removal

The Interstate Highway System has been expanded numerous times. The expansions have both created new designations and extended existing designations. For example,I-49,added to the system in the 1980s as a freeway inLouisiana,was designated as an expansion corridor, and FHWA approved the expanded route north fromLafayette, Louisiana,toKansas City, Missouri.The freeway exists today as separate completed segments, with segments under construction or in the planning phase between them.

In 1966, the FHWA designated the entire Interstate Highway System as part of the largerPan-American HighwaySystem,and at least two proposed Interstate expansions were initiated to help trade with Canada and Mexico spurred by theNorth American Free Trade Agreement(NAFTA). Long-term plans forI-69,which currently exists in several separate completed segments (the largest of which are inIndianaandTexas), is to have the highway route extend fromTamaulipas,Mexico toOntario,Canada. The plannedI-11will then bridge the Interstate gap betweenPhoenix, ArizonaandLas Vegas, Nevada,and thus form part of theCANAMEX Corridor(along withI-19,and portions ofI-10andI-15) betweenSonora,Mexico andAlberta,Canada.

Opposition, cancellations, and removals

Main article:Highway revolts in the United States

The fervor ofurban renewalled to the routing ofInterstate 81through the middle ofSyracuse's15th Ward in the 1960s. The viaduct is now slated for demolition.

Political opposition from residents canceled many freeway projects around the United States, including:

• I-40in Memphis, Tennessee was rerouted and part of the original I-40 is still in use as the eastern half ofSam Cooper Boulevard.
• I-66in theDistrict of Columbiawas abandoned in 1977.
• I-69was to continue past its terminus at Interstate 465 to intersect withInterstate 70andInterstate 65at the north split, northeast of downtownIndianapolis.Though local opposition led to the cancellation of this project in 1981, bridges and ramps for the connection into the "north split" remained until it was rebuilt in 2023.
• I-70inBaltimorewas supposed to run from the Baltimore Beltway (Interstate 695), which surrounds the city to terminate atI-95,the East Coast thoroughfare that runs through Maryland and Baltimore on a diagonal course, northeast to southwest; the connection was cancelled on the mid-1970s due to its routing throughGwynns Falls-Leakin Park,a wilderness urban park reserve following theGwynns Fallsstream through West Baltimore. This included the cancellation ofI-170,partially built and in use as US 40, and nicknamed the Highway to Nowhere. The freeway stub of I-70 inside the Beltway was renumbered MD 570 in 2014, but continues to bear I-70 signs.
• I-78in New York City was canceled along with portions ofI-278,I-478,andI-878.I-878 was supposed to be part of I-78, and I-478 and I-278 were to be spur routes.
• I-80in San Francisco was originally planned to travel past the city's Civic Center along the Panhandle Freeway intoGolden Gate Parkand terminate at the original alignment ofI-280/SR 1.The city canceled this and several other freeways in 1958. Similarly, more than 20 years later, Sacramento canceled plans to upgrade I-80 to Interstate Standards and rerouted the freeway on what was then I-880 that traveled north of Downtown Sacramento.
• I-83,southern extension of theJones Falls Expressway(southernI-83) inBaltimorewas supposed to run along the waterfront of thePatapsco River/Baltimore Harborto connect toI-95,bisecting historic neighborhoods ofFells PointandCanton,but the connection was never built.
• I-84inConnecticutwas once planned to fork east of Hartford, into anI-86to Sturbridge, Massachusetts, and I-84 to Providence, R.I. The plan was cancelled, primarily because of anticipated impact on a major Rhode Island reservoir. The I-84 designation was restored to the highway to Sturbridge, and other numbering was used for completed Eastern sections of what had been planned as part of I-84.
• I-95through theDistrict of ColumbiaintoMarylandwas abandoned in 1977. Instead it was rerouted toI-495 (Capital Beltway).The completed section is nowI-395.
• I-95was originally planned to run up theSouthwest Expresswayand meetI-93,where the two highways would travel along theCentral Arterythrough downtownBoston,but was rerouted onto theRoute 128beltway due to widespread opposition. This revolt also included the cancellation of theInner Belt,connecting I-93 toI-90and a cancelled section of theNorthwest Expresswaywhich would have carriedUS 3inside the Route 128 beltway, meeting withRoute 2inCambridge.

In addition to cancellations, removals of freeways are planned:

• I-81inSyracuse, New York,which bisects the city's 15th Ward neighborhood, is planned to be torn down and replaced with aboulevardthat accommodates pedestrians.Freeway traffic would be rerouted alongI-481.

Standards

Main article:Interstate Highway standards

TheAmerican Association of State Highway and Transportation Officials(AASHTO) has defined a set of standards that all new Interstates must meet unless a waiver from theFederal Highway Administration(FHWA) is obtained. One almost absolute standard is thecontrolled accessnature of the roads. With fewexceptions,traffic lights(and cross traffic in general) are limited totoll boothsandramp meters(metered flow control for lane merging duringrush hour).

Speed limits

Further information:Speed limits in the United StatesandNational Maximum Speed Law

I-95inColumbia, Maryland,built to modern standards.

A rural stretch ofI-5in California; two lanes in each direction are separated by a large grassymedianand cross-traffic is limited tograde separationssuch as this overpass.

Beingfreeways,Interstate Highways usually have the highestspeed limitsin 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 55 miles per hour (90 km/h), in accordance with federal law.

Typically, lower limits are established inNortheasternand coastal states, while higher speed limits are established in inland states west of theMississippi River.For example, the maximum speed limit is 75 mph (120 km/h) in northern Maine, varies between 50 and 70 mph (80 and 115 km/h)from southern Maine to New Jersey, and is 50 mph (80 km/h) in New York City and the District of Columbia.Currently, rural speed limits elsewhere generally range from 65 to 80 miles per hour (105 to 130 km/h). Several portions of various highways such asI-10andI-20in rural western Texas,I-80in Nevada between Fernley and Winnemucca (except around Lovelock) and portions ofI-15,I-70,I-80,andI-84in Utah have a speed limit of 80 mph (130 km/h). 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 onI-90is 50 mph (80 km/h) in downtownClevelandbecause of two sharp curves with a suggested limit of 35 mph (55 km/h) in a heavily congested area;I-70throughWheeling, West Virginia,has a maximum speed limit of 45 mph (70 km/h) through theWheeling Tunneland most of downtown Wheeling; andI-68has a maximum speed limit of 40 mph (65 km/h) throughCumberland, 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 ofI-35EinSt. Paul, Minnesota,for nearly 30 years in the courts, residents along the stretch of the freeway from the southern city limit to downtown successfully lobbied for a 45 mph (70 km/h) speed limit in addition to a prohibition on any vehicle weighing more than 9,000 pounds (4,100 kg)gross vehicle weight.I-93inFranconia Notch State Parkin northern New Hampshire has a speed limit of 45 mph (70 km/h) 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 70 mph (115 km/h) within theWasatch Front,Cedar City,andSt. Georgeareas, andI-25in New Mexico within theSanta FeandLas Vegasareas along withI-20in Texas along Odessa andMidlandandI-29in North Dakota along theGrand Forksarea have higher speed limits of 75 mph (120 km/h).

Other uses

As one of the components of theNational 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 theStrategic Highway Network,a system of roads identified as critical to theUS Department of Defense.

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 ascontraflow lane reversal,has been employed several times for hurricane evacuations. After public outcry regarding the inefficiency of evacuating from southern Louisiana prior toHurricane Georges' landfall in September 1998, government officials looked towards contraflow to improve evacuation times. InSavannah, Georgia,andCharleston, South Carolina,in 1999, lanes ofI-16andI-26were used in a contraflow configuration in anticipation ofHurricane Floydwith mixed results.

In 2004, contraflow was employed ahead ofHurricane Charleyin theTampa, Floridaarea and on theGulf Coastbefore the landfall ofHurricane Ivan;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 toHurricane Katrinaran much more smoothly.

According tourban 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.It is alsocommonly believedthe Interstate Highway System was built for the sole purpose of evacuating cities in the event ofnuclear warfare.While military motivations were present, the primary motivations were civilian.

Numbering system

Primary (one- and two-digit) Interstates

See also:List of Interstate Highways

Odd numbers run north–south with numbers increasing from west to east, while even numbers run east–west with numbers increasing from south to north.

I‑78andUS 22inBerks County, Pennsylvania(2008)

The numbering scheme for the Interstate Highway System was developed in 1957 by the American Association of State Highway and Transportation Officials (AASHTO). The association's present numbering policy dates back to August 10, 1973.Within the contiguous United States, primary Interstates—also called main line Interstates or two-digit Interstates—are assigned numbers less than 100.

While numerous exceptions do exist, there is a general scheme for numbering Interstates. Primary Interstates are assigned one- or two-digit numbers, while shorter routes (such as spurs, loops, and short connecting roads) are assigned three-digit numbers where the last two digits match the parent route (thus,I-294is a loop that connects at both ends toI-94,whileI-787is a short spur route attached toI-87). In the numbering scheme for the primary routes, 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 (to avoid confusion with theUS Highways,which increase from east to west and north to south).This numbering system usually holds true even if the local direction of the route does not match the compass directions. Numbersdivisibleby five are intended to be major arteries among the primary routes, carrying traffic long distances.Primary north–south Interstates increase in number fromI-5between Canada and Mexico along theWest CoasttoI‑95between Canada andMiami, Floridaalong theEast Coast.Major west–east arterial Interstates increase in number fromI-10betweenSanta Monica, California,andJacksonville, Florida,toI-90betweenSeattle, Washington,andBoston, Massachusetts,with two exceptions. There are no I-50 and I-60, as routes with those numbers would likely pass through states that currently have US Highways with the same numbers, which is generally disallowed under highway administration guidelines.

Several two-digit numbers are shared between unconnected road segments at opposite ends of the country for various reasons. Some such highways are incomplete Interstates (such asI-69andI-74) and some just happen to share route designations (such asI-76,I-84,I‑86,I-87,andI-88). Some of these were due to a change in the numbering system as a result of a new policy adopted in 1973. Previously, letter-suffixed numbers were used for long spurs off primary routes; for example, westernI‑84was I‑80N, as it went north fromI‑80.The new policy stated, "No new divided numbers (such asI-35WandI-35E,etc.) shall be adopted. "The new policy also recommended that existing divided numbers be eliminated as quickly as possible; however, anI-35WandI-35Estill exist in theDallas–Fort Worth metroplexin Texas, and anI-35WandI-35Ethat run throughMinneapolisandSaint Paul,Minnesota, still exist.Additionally, due to Congressional requirements, three sections of I-69 in southern Texas will be divided intoI-69W,I-69E,andI-69C(for Central).

AASHTO policy allows dual numbering to provide continuity between major control points.This is referred to as aconcurrencyor overlap. For example,I‑75andI‑85share the same roadway inAtlanta;this 7.4-mile (11.9 km) section, called theDowntown Connector,is labeled both I‑75 and I‑85. Concurrencies between Interstate and US Highway numbers are also allowed in accordance with AASHTO policy, as long as the length of the concurrency is reasonable.In rare instances, two highway designations sharing the same roadway are signed as traveling in opposite directions; one suchwrong-way concurrencyis found betweenWythevilleandFort Chiswell,Virginia, whereI‑81north andI‑77south are equivalent (with that section of road traveling almost due east), as are I‑81 south and I‑77 north.

Auxiliary (three-digit) Interstates

See also:List of auxiliary Interstate Highways

Examples of the auxiliary Interstate Highway numbering system. An odd hundreds digit means the route connects at only one end to the rest of the interstate system, known as a "spur route" (see I-310 and I-510 in image). An even hundreds digit means the route connects at both ends, which could be a bypass route (which has two termini) (see I-210 and I-810 in image) or a radial route (known also as a beltway, beltline, or circumferential route) (see I-610 in image).

Auxiliary Interstate Highways are circumferential, radial, or spur highways that principally serveurban 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 its parent Interstate Highway. Spur routes deviate from their parent and do not return; these are given an odd first digit. Circumferential and radial loop routes return to the parent, and are given an even first digit. 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 instance,I-190in Massachusetts is labeled north–south, whileI-195in New Jersey is labeled east–west. Some looped Interstate routes useinner–outer directionsinstead of compass directions, when the use of compass directions would create ambiguity. Due to the large number of these routes, auxiliary route numbers may be repeated in different states along the mainline.Some auxiliary highways do not follow these guidelines, however.

Alaska, Hawaii, and Puerto Rico

Map of routes inPuerto Ricothat receive funding from the Interstate program, but are not signed as Interstate Highways

Map of routes in Alaska that receive funding from the Interstate program, but are not signed as Interstate Highways

The Interstate Highway System also extends toAlaska,Hawaii,andPuerto Rico,even though they have no direct land connections to any other states or territories. However, their residents still pay federal fuel and tire taxes.

The Interstates in Hawaii, all located on the most populous island ofOahu,carry the prefixH.There are three one-digit routes in the state (H-1,H-2,andH-3) and one auxiliary route (H-201). These Interstates connect severalmilitaryandnavalbases together, as well as the important communities spread across Oahu, and especially within the urban core ofHonolulu.

Both Alaska and Puerto Rico also have public highways that receive 90 percent of their funding from the Interstate Highway program. TheInterstates of AlaskaandPuerto Ricoare numbered sequentially in order of funding without regard to the rules on odd and even numbers. They also carry the prefixesAandPR,respectively. However, these highways are signed according to their local designations, not their Interstate Highway numbers. Furthermore, these routes were neither planned according to nor constructed to the officialInterstate Highway standards.

Mile markers and exit numbers

On one- or two-digit Interstates, the mile marker numbering almost always begins at the southern or western state line. If an Interstate originates within a state, the numbering begins from the location where the road begins in the south or west. As with all guidelines for Interstate routes, however, numerous exceptions exist.

Three-digit Interstates with an even first number that form a complete circumferential (circle) bypass around a city feature mile markers that are numbered in a clockwise direction, beginning just west of an Interstate that bisects the circumferential route near a south polar location. In other words, mile marker 1 onI-465,a 53-mile (85 km) route around Indianapolis, is just west of its junction withI-65on the south side of Indianapolis (on the south leg of I-465), and mile marker 53 is just east of this same junction. An exception isI-495in theWashington metropolitan area,with mileposts increasing counterclockwise because part of that road is also part ofI-95.

Most Interstate Highways use distance-basedexit numbersso that the exit number is the same as the nearest mile marker. If multiple exits occur within the same mile, letter suffixes may be appended to the numbers in alphabetical order starting with A.A small number of Interstate Highways (mostly in the Northeastern United States) use sequential-based exit numbering schemes (where each exit is numbered in order starting with 1, without regard for the mile markers on the road). One Interstate Highway,I-19in Arizona, is signed with kilometer-based exit numbers. In the state of New York, most Interstate Highways use sequential exit numbering, with some exceptions.

Business routes

Standard Interstate shields

Markers for Business Loop Interstate 80 (left) and Business Spur Interstate 80 (right)

AASHTO defines a category of special routes separate from primary and auxiliary Interstate designations. These routes do not have to comply to Interstate construction or limited-access standards but are routes that may be identified and approved by the association. The same route marking policy applies to both US Numbered Highways and Interstate Highways; however,business routedesignations are sometimes used for Interstate Highways.Known asBusiness Loops and Business Spurs,these routes principally travel through the corporate limits of a city, passing through the central business district when the regular route is directed around the city. They also use a green shield instead of the red and blue shield.An example would beBusiness Loop Interstate 75atPontiac, Michigan,which follows surface roads into and through downtown. Sections of BL I-75's routing had been part ofUS 10andM-24,predecessors ofI-75in the area.

Financing

I‑787inWatervliet,New York, showing the exit 8diamond interchange

Interstate Highways and their rights-of-way are owned by the state in which they were built. The last federally owned portion of the Interstate System was theWoodrow Wilson Bridgeon theWashington Capital Beltway.The new bridge was completed in 2009 and is collectively owned by Virginia and Maryland.Maintenance is generally the responsibility of the state department of transportation. However, there are some segments of Interstate owned and maintained by local authorities.

Taxes and user fees

About 70 percent of the construction and maintenance costs of Interstate Highways in the United States have been paid through user fees, primarily thefuel taxescollected by the federal, state, and local governments. To a much lesser extent they have been paid for by tolls collected ontoll highwaysand bridges. The federal gasoline tax was first imposed in 1932 at one cent per gallon; during the Eisenhower administration, theHighway Trust Fund,established by the Highway Revenue Act in 1956, prescribed a three-cent-per-gallon fuel tax, soon increased to 4.5 cents per gallon. Since 1993 the tax has remained at 18.4 cents per gallon.Other excise taxes related to highway travel also accumulated in the Highway Trust Fund.Initially, that fund was sufficient for the federal portion of building the Interstate system, built in the early years with "10 cent dollars", from the perspective of the states, as the federal government paid 90% of the costs while the state paid 10%. The system grew more rapidly than the rate of the taxes on fuel and other aspects of driving (e. g., excise tax on tires).

The rest of the costs of these highways are borne by general fund receipts, bond issues, designated property taxes, and other taxes. The federal contribution is funded primarily throughfuel taxesand through transfers from the Treasury's general fund.Local government contributions are overwhelmingly from sources besides user fees.As decades passed in the 20th century and into the 21st century, the portion of the user fees spent on highways themselves covers about 57 percent of their costs, with about one-sixth of the user fees being sent to other programs, including themass transit systemsin large cities. Some large sections of Interstate Highways that were planned or constructed before 1956 are still operated as toll roads, for example theMassachusetts Turnpike(I-90), theNew York State Thruway(I-87 and I-90), andKansas Turnpike(I-35, I-335, I-470, I-70). Others have had their construction bonds paid off and they have become toll-free, such as theConnecticut Turnpike(I‑95, I-395), theRichmond-Petersburg Turnpikein Virginia (also I‑95), and theKentucky Turnpike(I‑65).

A view of I-75 in Atlanta, Georgia, featuringHOV lanesrunning alongside the median

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.This has led to the proliferation of toll roads (turnpikes) as the new method of building limited-access highways in suburban areas. Some Interstates are privately maintained (for example, the VMS company maintains I‑35 in Texas)to meet rising costs of maintenance and allow state departments of transportation to focus on serving the fastest-growing regions in their states.

Parts of the Interstate System might have to be tolled in the future to meet maintenance and expansion demands, as has been done with adding tollHOV/HOT lanesin cities such asAtlanta,Dallas,andLos Angeles.Although part of the tolling is an effect of theSAFETEA‑LUact, which has put an emphasis on toll roads as a means to reduce congestion,present federal law does not allow for a state to change a freeway section to a tolled section for all traffic.

Tolls

See also:Category:Tolled sections of Interstate Highways

AnI-76trailblazer along thePennsylvania Turnpikewith the black-on-yellow "Toll" sign

About 2,900 miles (4,700 km) of toll roads are included in the Interstate Highway System.While federal legislation initially banned the collection of tolls on Interstates, many of the toll roads on the system were either completed or under construction when the Interstate Highway System was established. Since these highways provided logical connections to other parts of the system, they were designated as Interstate highways.Congressalso decided that it was too costly to either build toll-free Interstates parallel to these toll roads, or directly repay all the bondholders who financed these facilities and remove the tolls. Thus, these toll roads weregrandfatheredinto the Interstate Highway System.

Toll roads designated as Interstates (such as theMassachusetts Turnpike) were typically allowed to continue collecting tolls, but are generally ineligible to receive federal funds for maintenance and improvements. Some toll roads that did receive federal funds to finance emergency repairs (notably theConnecticut Turnpike(I-95) following theMianus River Bridgecollapse) were required to remove tolls as soon as the highway's construction bonds were paid off. In addition, these toll facilities were grandfathered fromInterstate Highway standards.A notable example is the western approach to theBenjamin Franklin BridgeinPhiladelphia,whereI-676has a surface street section through a historic area.

Policies on toll facilities and Interstate Highways have since changed. TheFederal Highway Administrationhas allowed some states to collect tolls on existing Interstate Highways, while a recent extension ofI-376included a section ofPennsylvania Route 60that was tolled by thePennsylvania Turnpike Commissionbefore receiving Interstate designation. Also, newer toll facilities (like the tolled section of I-376, which was built in the early 1990s) must conform to Interstate standards. A new addition of theManual on Uniform Traffic Control Devicesin 2009 requires a black-on-yellow "Toll" sign to be placed above the Interstate trailblazer on Interstate Highways that collect tolls.

Legislation passed in 2005 known asSAFETEA-LU,encouraged states to construct new Interstate Highways through "innovative financing" methods. SAFETEA-LU facilitated states to pursue innovative financing by easing the restrictions on building interstates as toll roads, either through state agencies or throughpublic–private partnerships.However, SAFETEA-LU left in place a prohibition of installing tolls on existing toll-free Interstates, and states wishing to toll such routes to finance upgrades and repairs must first seek approval from Congress. Many states have started usingHigh-occupancy toll laneand other partial tolling methods, whereby certain lanes of highly congested freeways are tolled, while others are left free, allowing people to pay a fee to travel in less congested lanes. Examples of recent projects to add HOT lanes to existing freeways include theVirginia HOT laneson the Virginia portions of theCapital Beltwayand other related interstate highways (I-95, I-495, I-395) and the addition of express toll lanes toInterstate 77 in North Carolinain theCharlotte metropolitan area.

Chargeable and non-chargeable Interstate routes

Interstate Highways financed with federal funds are known as "chargeable" Interstate routes, and are considered part of the 42,000-mile (68,000 km) network of highways. Federal laws also allow "non-chargeable" Interstate routes, highways funded similarly to state and US Highways to be signed as Interstates, if they both meet the Interstate Highway standards and are logical additions or connections to the system.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

Interstate shield

Several Interstate shield design proposals submitted by the Texas Highway Department

Interstate Highways are signed by a number placed on a red, white, and bluesign.The shield design itself is aregistered trademarkof theAmerican Association of State Highway and Transportation Officials.The colors red, white, and blue were chosen because they are the colors of theAmerican flag.In the original design, the name of the state was displayed above the highway number, but in many states, this area is now left blank, allowing for the printing of larger and more-legible digits. Signs with the shield alone are placed periodically throughout each Interstate asreassurance markers.These signs usually measure 36 inches (91 cm) high, and are 36 inches (91 cm) wide for two-digit Interstates or 45 inches (110 cm) for three-digit Interstates.

Interstate business loops and spurs use a special shield in which 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.The green shield is employed to mark the main route through a city's central business district, which intersects the associated Interstate at one (spur) or both (loop) ends of the business route. The route usually traverses the main thoroughfare(s) of the city's downtown area or other major business district.A city may have more than one Interstate-derived business route, depending on the number of Interstates passing through a city and the number of significant business districts therein.

Over time, the design of the Interstate shield has changed. In 1957 the Interstate shield designed byTexas Highway Departmentemployee Richard Oliver was introduced, the winner of a contest that included 100 entries;at the time, the shield color was a dark navy blue and only 17 inches (43 cm) wide.TheManual on Uniform Traffic Control Devices(MUTCD) standards revised the shield in the 1961,1971,and 1978editions.

Exit numbering

The majority of Interstates haveexit numbers.Like other highways, Interstates featureguide signsthat listcontrol citiesto help direct drivers through interchanges and exits toward their desired destination. Alltraffic signsandlanemarkings on the Interstates are supposed to be designed in compliance with theManual 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.Caltranscommonly 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.

In 2010–2011, theIllinois State Toll Highway Authorityposted 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.

Exit numbers correspond to Interstate mileage markers in most states. OnI‑19inArizona,however, length is measured in kilometers instead of miles because, at the time of construction,a push for the United States to changeto ametric systemof 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);proximity to metric-using Mexico may also have been a factor, as I‑19 indirectly connects I‑10 to theMexican Federal Highwaysystem via surface streets inNogales.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 theNew York State Thruway,use sequential exit-numbering schemes. Exits on the New York State Thruway count up fromYonkerstraveling north, and then west from Albany. I‑87 in New York State is numbered in three sections. The first section makes up theMajor Deegan Expresswayinthe Bronx,with interchanges numbered sequentially from 1 to 14. The second section of I‑87 is a part of theNew York State Thruwaythat starts in Yonkers (exit 1) and continues north to Albany (exit 24); at Albany, the Thruway turns west and becomes I‑90 for exits 25 to 61. From Albany north to the Canadian border, the exits on I‑87 are numbered sequentially from 1 to 44 along theAdirondack Northway.This often leads to confusion as there is more than one exit on I‑87 with the same number. For example, exit 4 on Thruway section of I‑87 connects with the Cross County Parkway in Yonkers, but exit 4 on the Northway is the exit for the Albany airport. These two exits share a number but are located 150 miles (240 km) 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 (87,88,89) 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.ThePennsylvania Turnpikeuses both mile marker numbers and sequential numbers. Mile marker numbers are used for signage, while sequential numbers are used for numbering interchanges internally. TheNew 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.

Sign locations

There are four common signage methods on Interstates:

• Locating a sign on the ground to the side of the highway, mostly the right, and is used to denote exits, as well asrest areas,motorist services such as gas and lodging, recreational sites, and freeway names
• Attaching the sign to an overpass
• Mounting on fullgantriesthat bridge the entire width of the highway and often show two or more signs
• Mounting on half-gantries that are located on one side of the highway, like a ground-mounted sign

Statistics

Motor vehicles on I-95 in Miami

Volume

• Heaviest traveled:379,000 vehicles per day:I-405in Los Angeles, California (2011 estimate).

Elevation

• Highest:11,158 feet (3,401 m):I-70in theEisenhower Tunnelat theContinental Dividein theColoradoRocky Mountains.
• Lowest (land):−52 feet (−16 m):I-8at theNew RivernearSeeley, California.
• Lowest (underwater):−103 feet (−31 m):I-95in theFort McHenry Tunnelunder theBaltimore Inner Harbor.

Length

• Longest (east–west):3,020.54 miles (4,861.09 km):I-90fromBoston, Massachusetts,toSeattle, Washington.
• Longest (north–south):1,908 mi (3,071 km):I-95from theCanadian bordernearHoulton, Maine,toMiami, Florida.
• Shortest (two-digit):1.40 mi (2.25 km):I-69WinLaredo, Texas.
• Shortest (auxiliary):0.70 mi (1.13 km):I-878inQueens,New York,New York.
• Longest segment between state lines:877 mi (1,411 km):I-10 in Texasfrom theNew Mexicostate line nearEl Pasoto theLouisianastate line nearOrange, Texas.
• Shortest segment between state lines:453 ft (138 m):I-95/I-495(Capital Beltway) on theWoodrow Wilson Bridgeacross thePotomac Riverwhere they briefly cross the southernmost tip of theDistrict of Columbiabetween its borders withMarylandandVirginia.
• Longest concurrency:278.4 mi (448.0 km):I-80andI-90;Gary, Indiana,toElyria, Ohio.

States

• Most states served by an Interstate:15 states plus the District of Columbia:I-95throughFlorida,Georgia,South Carolina,North Carolina,Virginia,DC,Maryland,Delaware,Pennsylvania,New Jersey,New York,Connecticut,Rhode Island,Massachusetts,New Hampshire,andMaine.
• Most Interstates in a state:32 routes: New York, totaling 1,750.66 mi (2,817.41 km)
• Most primary Interstates in a state:13 routes: Illinois
• Most Interstate mileage in a state:3,233.45 mi (5,203.73 km): Texas, in 17 different routes.
• Fewest Interstates in a state:3 routes: Delaware, New Mexico, North Dakota, and Rhode Island. Puerto Rico also has 3 routes.
• Fewest primary Interstates in a state:1 route: Delaware, Maine, and Rhode Island (I-95 in each case).
• Least Interstate mileage in a state:40.61 mi (65.36 km): Delaware, in 3 different routes.

Impact and reception

Following the passage of the Federal Aid Highway Act of 1956, passenger rail declined sharply as did freight rail for a short time, but the trucking industry expanded dramatically and the cost of shipping and travel fell sharply.Suburbanizationbecame possible, with the rapid growth of larger, sprawling, and more car-dependent housing than was available in central cities, enablingracial segregationbywhite flight.A sense of isolationism developed in suburbs, with suburbanites wanting to keep urban areas disconnected from the suburbs.Tourism dramatically expanded, creating a demand for more service stations, motels, restaurants and visitor attractions. The Interstate System was the basis for urban expansion in the Sun Belt, and many urban areas in the region are thus very car-dependent.The highways may have contributed to increased economic productivity in, and thereby increased migration to, theSun Belt.In rural areas, towns and small cities off the grid lost out as shoppers followed the interstate and new factories were located near them.

The system had a profound effect on interstate shipping. The Interstate Highway System was being constructed at the same time as theintermodal shipping containermade its debut. These containers could be placed on trailers behind trucks and shipped across the country with ease. A new road network and shipping containers that could be easily moved from ship to train to truck, meant that overseas manufacturers and domestic startups could get their products to market quicker than ever, allowing for accelerated economic growth.Forty years after its construction, the Interstate Highway system returned on investment, making $6for every $1 spent on the project.According to research by theFHWA,"from 1950 to 1989, approximately one-quarter of the nation's productivity increase is attributable to increased investment in the highway system."

The system had a particularly strong effect in Southern states, where major highways were inadequate.The new system facilitated the relocation of heavy manufacturing to the South and spurred the development of Southern-based corporations likeWalmart(in Arkansas) andFedEx(in Tennessee).

The Interstate Highway System also dramatically affected American culture, contributing to cars becoming more central to the American identity. Before, driving was considered an excursion that required some amount of skill and could have some chance of unpredictability. With the standardization of signs, road widths and rules, certain unpredictabilities lessened. Justin Fox wrote, "By making road more reliable and by making Americans more reliant on them, they took away most of the adventure and romance associated with driving."

The Interstate Highway System has been criticized for contributing to the decline of some cities that were divided by Interstates, and for displacing minority neighborhoods in urban centers.Between 1957 and 1977, the Interstate System alone displaced over 475,000 households and one million people across the country.Highways have also been criticized for increasing racial segregation by creating physical barriers between neighborhoods,and for overall reductions in available housing and population in neighborhoods affected by highway construction.Other critics have blamed the Interstate Highway System for the decline ofpublic transportation in the United Statessince the 1950s,which minorities and low-income residents are three to six times more likely to use.Previous highways, such asUS 66,were also bypassed by the new Interstate system, turning countless rural communities along the way into ghost towns.The Interstate System has also contributed to continued resistance against new public transportation.

The Interstate Highway System had a negative impact on minority groups, especially in urban areas. Even though the government usedeminent domainto obtain land for the Interstates, it was still economical to build where land was cheapest. This cheap land was often located in predominately minority areas.Not only were minority neighborhoods destroyed, but in some cities the Interstates were used to divide white and minority neighborhoods.These practices were common in cities both in the North and South, includingNashville,Miami,Chicago,Detroit,and many other cities. The division and destruction of neighborhoods led to the limitation of employment and other opportunities, which deteriorated the economic fabric of neighborhoods.Neighborhoods bordering Interstates have a much higher level of particulateair pollutionand are more likely to be chosen for polluting industrial facilities.

See also

• Highway systems by country
• List of controlled-access highway systems
• Non-motorized access on freeways

Further reading

• Arcadi, Teal (2022). "Partisanship and Permanence: How Congress Contested the Origins of the Interstate Highway System and the Future of American Infrastructure".Modern American History.Vol. 5. pp.53–77.doi:10.1017/mah.2022.4.
• Browning, Edgar A (2011).Roadbuilding Construction Equipment at Work: Building the Interstate Highways through New England's Green Mountains.Icongrafix.ISBN978-1-58388-277-1.
• Friedlaender, Ann Fetter (1965).The Interstate Highway System. A Study in Public Investment.Amsterdam: North-Holland Publishing.OCLC498010.
• Hanlon, Martin D. (1997).You Can Get There from Here: How the Interstate Highways Transformed America.New York: Basingstoke.ISBN978-0-312-12909-5.
• Lewis, Tom (1997).Divided Highways: Building the Interstate Highways, Transforming American Life.New York: Viking.ISBN978-0-670-86627-4.
• Lichter, Daniel T.; Fuguitt, Glenn V. (December 1980). "Demographic Response to Transportation Innovation: The Case of the Interstate Highway".Social Forces.Vol. 59, no. 2. pp.492–512.doi:10.1093/sf/59.2.492.JSTOR2578033.
• Rose, Mark H. (1990).Interstate: Express Highway Politics 1939–1989.Knoxville: University of Tennessee Press.ISBN978-0-87049-671-4.

External links

Template:Attached KML/Interstate Highway System

KML is not from Wikidata

• Geographic data related toInterstate Highway SystematOpenStreetMap
• Dwight D. Eisenhower National System of Interstate and Defense Highways,Federal Highway Administration (FHWA)
• Route Log and Finder List,FHWA
• Turner-Fairbank Highway Research Center,FHWA
• Interstate Highway System,Dwight D. Eisenhower Presidential Library and Museum
• "Keep on Trucking?: Would you pay more in taxes to fix roads and rail?",NOWon PBS