| Dwight D. Eisenhower National System of Interstate and Defense Highways | |
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   Highway shields for Interstate 80, Business Loop Interstate 80, and the Eisenhower Interstate System  | |
Primary Interstate Highways in the 48 contiguous states.Alaska, Hawaii, and Puerto Rico also have Interstate Highways. | |
| System information | |
| Length | 48,890 mi[a] (78,680 km) |
| Formed | June 29, 1956; 69 years ago (1956-06-29)[1] |
| Highway names | |
| Interstates | Interstate X (I-X) |
| System links | |
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World War II 34th President of the United States
First Term Second Term Presidential campaigns Post-Presidency   | ||
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 highways that forms part of theNational Highway System in theUnited States. The system extends throughout thecontiguous United States and has routes inHawaii,Alaska, andPuerto Rico.
In the 20th century, theUnited States Congress began 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 System was 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. Eisenhower became president in 1953,his administration developed 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".[3] In the two decades following the 1956 Highway Act, the construction of the freeways displaced one million people,[4] and as a result of the manyfreeway revolts during 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 $634 billion in 2024). The system has continued to expand and grow as additional federal funding has provided for new routes to be added, and manyfuture Interstate Highways are 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 strips between lanes of oncoming traffic,breakdown lanes, avoidingat-grade intersections, notraffic lights, and complying with federaltraffic sign specifications. 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 tax and transfers from theTreasury's general fund.[5] Though federal legislation initially banned the collection of tolls, some Interstate routes aretoll roads, either because they weregrandfathered into the system or because subsequent legislation has allowed for tolling of Interstates in some cases.
As of 2022[update], about one quarter of all vehicle miles driven in the country used the Interstate Highway System,[6] which has a total length of 48,890 miles (78,680 km).[2] 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.[7]
The United States government's efforts to construct a national network of highways began on anad hoc basis with the passage of theFederal Aid Road Act of 1916, which provided $75 million over a five-year period formatching funds to the states for the construction and improvement of highways.[8] The nation's revenue needs associated withWorld War I prevented 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"[9] during a gathering of the State Highway Officials and Highway Industries Association at the Congress Hotel in Chicago.[10] 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.[9]
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 Ellipse near theWhite House on July 7, theMotor Transport Corps convoy needed 62 days to drive 3,200 miles (5,100 km) on theLincoln Highway to thePresidio of San Francisco along 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.[11]
Dwight Eisenhower, then a 28-year-oldbrevet lieutenant colonel,[12] 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."[11]
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.[13] 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.[13]
TheBureau of Public Roads asked theArmy to provide a list of roads that it considered necessary for national defense.[14] In 1922, GeneralJohn J. Pershing, former head of theAmerican Expeditionary Force in 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.[15]
A boom in road construction followed throughout the decade of the 1920s, with such projects as theNew York parkway system constructed 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 Highways system. By the late 1930s, planning had expanded to a system of new superhighways.
In 1938, PresidentFranklin D. Roosevelt gaveThomas MacDonald, chief at the Bureau of Public Roads, a hand-drawn map of the United States marked with eight superhighway corridors for study.[16] In 1939, Bureau of Public Roads Division of Information chiefHerbert S. Fairbank wrote 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.[17]
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."[11] Eisenhower also gained an appreciation of theReichsautobahn system, the first "national" implementation of modern Germany'sAutobahn network, as a necessary component of a national defense system while he was serving asSupreme Commander ofAllied Forces in Europe duringWorld War II.[18] In 1954, Eisenhower appointed GeneralLucius D. Clay to head a committee charged with proposing an interstate highway system plan.[19] 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.[20]
Clay's committee proposed a 10-year, $100 billion program ($1.17 trillion in2024), which would build 40,000 miles (64,000 km) ofdivided highways linking 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 publicbonds as 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 agasoline tax.[21] In June 1956, Eisenhower signed theFederal Aid Highway Act of 1956 into 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 afreeway with at least four lanes and no at-grade crossings.[22]
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.[23] Assisting in the planning wasCharles Erwin Wilson, who was still head ofGeneral Motors when President Eisenhower selected him as Secretary of Defense in January 1953.
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 66 to what is now designatedInterstate 44.[24] On August 13, 1956, work began onUS 40 (now I-70) in St. Charles County.[25][24]
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-70 as the first project in the United States completed under the provisions of the new Federal-Aid Highway Act of 1956.[24]
ThePennsylvania Turnpike could also be considered one of the first Interstate Highways, and is nicknamed "Grandfather of the Interstate System".[25] On October 1, 1940, 162 miles (261 km) of the highway now designated I‑70 and I‑76 opened betweenIrwin andCarlisle. TheCommonwealth of Pennsylvania refers to the turnpike as the Granddaddy of the Pikes, a reference toturnpikes.[24]
Milestones in the construction of the Interstate Highway System include:
The initial cost estimate for the system was $25 billion over 12 years; it ended up costing $114 billion (equivalent to $425 billion in 2006[37] or $634 billion in 2024[38]) and took 35 years.[39]
The system was proclaimed complete in 1992, but two of the original Interstates—I-95 andI-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,[40] 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 Project started in 2010[41] and partially opened on September 22, 2018, which was already enough to fill the gap.[40]
However, I-70 remains discontinuous inPennsylvania, because of the lack of a direct interchange with thePennsylvania Turnpike at the eastern end of theconcurrency nearBreezewood. 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.[42] Solutions have been proposed to eliminate the discontinuity, but they have been blocked by local opposition, fearing a loss of business.[43]
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.[44]
In 1966, the FHWA designated the entire Interstate Highway System as part of the largerPan-American Highway System,[45] 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 inIndiana andTexas), is to have the highway route extend fromTamaulipas, Mexico toOntario, Canada. The plannedI-11 will then bridge the Interstate gap betweenPhoenix, Arizona andLas Vegas, Nevada, and thus form part of theCANAMEX Corridor (along withI-19, and portions ofI-10 andI-15) betweenSonora, Mexico andAlberta, Canada.
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Political opposition from residents canceled many freeway projects around the United States, including:
In addition to cancellations, removals of freeways are planned:
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 access nature of the roads. With fewexceptions,traffic lights (and cross traffic in general) are limited totoll booths andramp meters (metered flow control for lane merging duringrush hour).
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Beingfreeways, Interstate Highways usually have the highestspeed limits in a given area. Speed limits are determined by individual states. From 1975 to 1986, the maximum speed limit on any highway in the United States was 55 miles per hour (90 km/h), in accordance with federal law.[49]
Typically, lower limits are established inNortheastern and coastal states, while higher speed limits are established in inland states west of theMississippi River.[50] 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)[51] from southern Maine to New Jersey, and is 50 mph (80 km/h) in New York City and the District of Columbia.[50] 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-10 andI-20 in rural western Texas,I-80 in Nevada between Fernley and Winnemucca (except around Lovelock) and portions ofI-15,I-70,I-80, andI-84 in 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-90 is 50 mph (80 km/h) in downtownCleveland because of two sharp curves with a suggested limit of 35 mph (55 km/h) in a heavily congested area;I-70 throughWheeling, West Virginia, has a maximum speed limit of 45 mph (70 km/h) through theWheeling Tunnel and most of downtown Wheeling; andI-68 has 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-35E inSt. 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-93 inFranconia Notch State Park in 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. George areas, andI-25 in New Mexico within theSanta Fe andLas Vegas areas along withI-20 in Texas along Odessa andMidland andI-29 in North Dakota along theGrand Forks area have higher speed limits of 75 mph (120 km/h).
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.[52]
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-16 andI-26 were used in a contraflow configuration in anticipation ofHurricane Floyd with mixed results.[53]
In 2004, contraflow was employed ahead ofHurricane Charley in theTampa, Florida area and on theGulf Coast before the landfall ofHurricane Ivan;[54] 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 Katrina ran much more smoothly.[55]
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.[56][57] It is alsocommonly believed the 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.[58][59]
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.[60] Within the contiguous United States, primary Interstates—also called main line Interstates or two-digit Interstates—are assigned numbers less than 100.[60]
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-294 is a loop that connects at both ends toI-94, whileI-787 is 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).[61] This numbering system usually holds true even if the local direction of the route does not match the compass directions. Numbersdivisible by five are intended to be major arteries among the primary routes, carrying traffic long distances.[62][63] Primary north–south Interstates increase in number fromI-5 between Canada and Mexico along theWest Coast toI‑95 between Canada andMiami, Florida along theEast Coast. Major west–east arterial Interstates increase in number fromI-10 betweenSanta Monica, California, andJacksonville, Florida, toI-90 betweenSeattle, 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.[60][64]
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-69 andI-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‑84 was I‑80N, as it went north fromI‑80. The new policy stated, "No new divided numbers (such asI-35W andI-35E, etc.) shall be adopted." The new policy also recommended that existing divided numbers be eliminated as quickly as possible; however, anI-35W andI-35E (East and West) still exist in theDallas–Fort Worth metroplex in Texas, and anI-35W andI-35E that run throughMinneapolis andSaint Paul, Minnesota, still exist.[60] Additionally, due to Congressional requirements, three sections of I-69 in southern Texas will be divided intoI-69W,I-69E, andI-69C (for Central).[65]
AASHTO policy allows dual numbering to provide continuity between major control points.[60] This is referred to as aconcurrency or overlap. For example,I‑75 andI‑85 share 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.[60] In rare instances, two highway designations sharing the same roadway are signed as traveling in opposite directions; one suchwrong-way concurrency is found betweenWytheville andFort Chiswell, Virginia, whereI‑81 north andI‑77 south are equivalent (with that section of road traveling almost due east), as are I‑81 south and I‑77 north.
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-190 in Massachusetts is labeled north–south, whileI-195 in New Jersey is labeled east–west. Some looped Interstate routes useinner–outer directions instead 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.[66] Some auxiliary highways do not follow these guidelines, however.
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 severalmilitary andnaval bases 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 Alaska andPuerto Rico are numbered sequentially in order of funding without regard to the rules on odd and even numbers. They also carry the prefixesA andPR, 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.[67]
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. For instance,I-86 dips into Pennsylvania for just 1.5 miles at exit 60 which maintains mile marker numbering for New York.
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-65 on 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-495 in theWashington metropolitan area, with mileposts increasing counterclockwise because part of that road is also part ofI-95.
Most Interstate Highways use distance-basedexit numbers so 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.[68] 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-19 in Arizona, is signed with kilometer-based exit numbers. In the state of New York, most Interstate Highways use sequential exit numbering, with some exceptions.[69]
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 route designations are sometimes used for Interstate Highways.[70] 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.[70] An example would beBusiness Loop Interstate 75 atPontiac, Michigan, which follows surface roads into and through downtown. Sections of BL I-75's routing had been part ofUS 10 andM-24, predecessors ofI-75 in the area.
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 Bridge on theWashington Capital Beltway. The new bridge was completed in 2009 and is collectively owned by Virginia and Maryland.[71] Maintenance is generally the responsibility of the state department of transportation. However, there are some segments of Interstate owned and maintained by local authorities.
About 70 percent of the construction and maintenance costs of Interstate Highways in the United States have been paid through user fees, primarily thefuel taxes collected by the federal, state, and local governments. To a much lesser extent they have been paid for by tolls collected ontoll highways and 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.[72] Other excise taxes related to highway travel also accumulated in the Highway Trust Fund.[72] 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 taxes and through transfers from the Treasury's general fund.[5] Local government contributions are overwhelmingly from sources besides user fees.[73] 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 systems in 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 Turnpike in Virginia (also I‑95), and theKentucky Turnpike (I‑65).
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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.[74] 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)[75] 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 lanes in cities such asAtlanta,Dallas, andLos Angeles. Although part of the tolling is an effect of theSAFETEA‑LU act, which has put an emphasis on toll roads as a means to reduce congestion,[76][77] present federal law does not allow for a state to change a freeway section to a tolled section for all traffic.[78]
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About 2,900 miles (4,700 km) of toll roads are included in the Interstate Highway System.[79] 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.Congress also 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 weregrandfathered into the Interstate Highway System.[80]
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 Bridge collapse) 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 Bridge inPhiladelphia, whereI-676 has a surface street section through a historic area.
Policies on toll facilities and Interstate Highways have since changed. TheFederal Highway Administration has allowed some states to collect tolls on existing Interstate Highways, while a recent extension ofI-376 included a section ofPennsylvania Route 60 that was tolled by thePennsylvania Turnpike Commission before 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 Devices in 2009 requires a black-on-yellow "Toll" sign to be placed above the Interstate trailblazer on Interstate Highways that collect tolls.[81]
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 lane and 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 lanes on the Virginia portions of theCapital Beltway and other related interstate highways (I-95, I-495, I-395) and the addition of express toll lanes toInterstate 77 in North Carolina in theCharlotte metropolitan area.
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.[82][83] 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, unless they are granted a design waiver by theFederal Highway Administration (FHWA).[67]
Interstate Highways are signed by a number placed on a red, white, and bluesign. The shield design itself is aregistered trademark of theAmerican Association of State Highway and Transportation Officials.[84] 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.[85]
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.[85] 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.[86] 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.[87]
Over time, the design of the Interstate shield has changed. In 1957 the Interstate shield designed byTexas Highway Department employee Richard Oliver was introduced, the winner of a contest that included 100 entries;[88][89] at the time, the shield color was a dark navy blue and only 17 inches (43 cm) wide.[90] TheManual on Uniform Traffic Control Devices (MUTCD) standards revised the shield in the 1961,[91] 1971,[92] and 1978[93] editions.
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The majority of Interstates haveexit numbers. Like other highways, Interstates featureguide signs that listcontrol cities to help direct drivers through interchanges and exits toward their desired destination. Alltraffic signs andlane markings 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.Caltrans commonly installs exit number signage only when a freeway or interchange is built, reconstructed, retrofitted, or repaired, and it is usually tacked onto the top-right corner of an already existing sign. Newer signs along the freeways follow this practice as well. Most exits along California's Interstates now have exit number signage, particularly in rural areas. California, however, still does not use mileposts, although a few exist for experiments or for special purposes.[94][self-published source]
In 2010–2011, theIllinois State Toll Highway Authority posted all new mile markers to be uniform with the rest of the state on I‑90 (Jane Addams Memorial/Northwest Tollway) and the I‑94 section of the Tri‑State Tollway, which previously had matched the I‑294 section starting in the south at I‑80/I‑94/IL Route 394. This also applied to the tolled portion of the Ronald Reagan Tollway (I-88). The tollway also added exit number tabs to the exits.[citation needed]
Exit numbers correspond to Interstate mileage markers in most states. OnI‑19 inArizona, however, length is measured in kilometers instead of miles because, at the time of construction,a push for the United States to change to ametric system of measurement had gained enough traction that it was mistakenly assumed that all highway measurements would eventually be changed to metric (and some distance signs retain metric distances);[95] proximity to metric-using Mexico may also have been a factor, as I‑19 indirectly connects I‑10 to theMexican Federal Highway system 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 fromYonkers traveling north, and then west from Albany. I‑87 in New York State is numbered in three sections. The first section makes up theMajor Deegan Expressway inthe Bronx, with interchanges numbered sequentially from 1 to 14. The second section of I‑87 is a part of theNew York State Thruway that 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.[96] ThePennsylvania Turnpike uses both mile marker numbers and sequential numbers. Mile marker numbers are used for signage, while sequential numbers are used for numbering interchanges internally. 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.
There are four common signage methods on Interstates:
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.[108][citation needed]Suburbanization became possible, with the rapid growth of larger, sprawling, and more car-dependent housing than was available in central cities, enablingracial segregation bywhite flight.[109][110][111] A sense of isolationism developed in suburbs, with suburbanites wanting to keep urban areas disconnected from the suburbs.[109] 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.[112] The highways may have contributed to increased economic productivity in, and thereby increased migration to, theSun Belt.[113] In rural areas, towns and small cities off the grid lost out as shoppers followed the interstate and new factories were located near them.[114]
The system had a profound effect on interstate shipping. The Interstate Highway System was being constructed at the same time as theintermodal shipping container made 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.[115] Forty years after its construction, the Interstate Highway system returned on investment, making $6[among whom?] for every $1 spent on the project.[116][better source needed] 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."[117]
The system had a particularly strong effect in Southern states, where major highways were inadequate[citation needed]. 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).[115]
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."[115]
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.[3] Between 1957 and 1977, the Interstate System alone displaced over 475,000 households and one million people across the country.[4] Highways have also been criticized for increasing racial segregation by creating physical barriers between neighborhoods,[118] and for overall reductions in available housing and population in neighborhoods affected by highway construction.[119] Other critics have blamed the Interstate Highway System for the decline ofpublic transportation in the United States since the 1950s,[120] which minorities and low-income residents are three to six times more likely to use.[121] Previous highways, such asUS 66, were also bypassed by the new Interstate system, turning countless rural communities along the way into ghost towns.[122] The Interstate System has also contributed to continued resistance against new public transportation.[109]
The Interstate Highway System had a negative impact on minority groups, especially in urban areas. Even though the government usedeminent domain to 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.[112] Not only were minority neighborhoods destroyed, but in some cities the Interstates were used to divide white and minority neighborhoods.[109] 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.[121] Neighborhoods bordering Interstates have a much higher level of particulateair pollution and are more likely to be chosen for polluting industrial facilities.[121]
Proposed I-41 in Wisconsin and partly completed I-74 in North Carolina respectively are possible and current exceptions not adhering to the guideline. It is not known if the US Highways with the same numbers will be retained in the states upon completion of the Interstate routes.
Geographic data related toInterstate Highway System atOpenStreetMap PrimaryInterstate Highways | |
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Routes initalics are no longer a part of the system. Major Interstates are highlighted. | |
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