Interstate Highway System

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The Dwight D. Eisenhower National System of Interstate and Defense Highways, commonly called the Interstate Highway System, is a network of freeways in the United States. The Interstate Highway System is a separate system within the larger National Highway System. The entire system, as of October 2002, had a total length of 46,726 miles (75,198 km).^[1]

While Interstate Highways usually receive substantial federal funding and comply with federal standards, they are owned, built, and operated by the states in which they are located. The only exception is the federally owned Woodrow Wilson Bridge on the Capital Beltway (I-95/I-495).

Interstate Highways in the 48 contiguous states

A rural stretch of Interstate 5 in California, with two lanes in each direction separated by a large grassy median, and with cross-traffic limited to overpasses and underpasses.

The system serves all major U.S. cities. Unlike counterparts in most other industrialized countries, many Interstates pass through downtown areas. This facilitated the emergence of automobile-oriented postwar suburban development patterns, a phenomenon pejoratively named "urban sprawl."

The system is prominent in American daily life. The distribution of virtually all goods and services involve Interstate Highways at some point. Residents of American cities commonly use urban Interstates to travel to employment. The vast majority of long-distance travel, whether for vacation or business, uses the national road network;^[2] of these trips, about one-third (by the total number of miles driven in the country in 2003) utilize the Interstate system.^[3]

[edit] History

Commemorative sign introduced in 1993. Though the system was established during Dwight D. Eisenhower's presidency, the five stars commemorate his rank as General of the Army during World War II

The interstate system was authorized by the Federal-Aid Highway Act of 1956, popularly known as the National Interstate and Defense Highways Act of 1956. It had been lobbied for by major U.S. automobile manufacturers and championed by President Dwight D. Eisenhower, who was influenced by both his experiences as a young soldier crossing the country in 1919 following the route of the Lincoln Highway and his appreciation of the German autobahn network.

Planning for a system of new superhighways began in the late 1930s, even before federal commitment to build the Interstate highway system came in the 1950s. By the 1920s, highways such as the New York parkway system had been built as part of local or state highway systems. As automotive traffic increased, planners saw a need for such an interconnected national system to supplement the existing, largely non-freeway, United States Numbered Highway system. The publication General location of national system of interstate highways maps out what became the interstate system, and is informally known as the Yellow Book.[1]

Although construction on the Interstate Highway system continues, it was officially regarded as complete in 1991 (though 1.5 miles of the original planned system remain unconstructed as of 2005 ^[1]). The initial cost estimate for the system was $25 billion over twelve years; it ended up costing $114 billion, taking 35 years to complete ^{[citation needed]}.

The removal of the last traffic signal on Interstate 90 in Wallace, Idaho on September 15, 1991 is often cited as the completion of the Interstate System. However, due to the cancellation of the Somerset Freeway, Interstate 95 has not been completed in Pennsylvania and New Jersey; the Pennsylvania Turnpike/Interstate 95 Interchange Project will complete that route, the last section of the original (1947) plans to be completed (though a few routes, like Interstate 80 in central Ohio, have been relocated). Several other routes have non-freeway sections (see list of gaps on Interstate Highways), but are considered to be complete.

Missouri and Kansas have laid claims that I-70 in those states was the first interstate (Missouri also says I-44 is one of the first). The first three contracts under the new program were signed in Missouri on August 2, 1956. Kansas claims that it was the first to start paving after the act and that the Kansas portion of I-70 was the first complete section. However construction and planning on those roads had been underway before the highway act. The Pennsylvania Turnpike which opened on October 1, 1940 claims to be the first limited-access, divided highway in the country.[2]

[edit] Standards

Main article: Interstate Highway standards

The American Association of State Highway and Transportation Officials (AASHTO) has defined a set of standards that all new Interstates must meet unless a waiver from the Federal Highway Administration (FHWA) is obtained. These standards have become stricter over the years. One almost absolute standard is the controlled access nature of the roads. With few exceptions, traffic lights (and cross traffic in general) are limited to toll booths and ramp meters (metered flow control for lane merging during rush hours).

[edit] Speed limits

Interstate Highways often have the highest speed limits in a given area. Speed limits are determined by individual states. Rural limits range from 65 to 80 mph (100 to 130 km/h) typically with the lower limits in the more populated northeastern states and the higher speeds in the western states. Urban interstate speed limits are generally 50 to 65 mph (80 to 100 km/h) across the country.

Further information: Speed limits in the United States

[edit] Dual-purpose design

In addition to being designed to support automobile and heavy truck traffic, interstate highways are also designed for use in military and civil defense operations within the United States, particularly troop movements. However, it is not the case, as is often believed, that the highway system was designed to support aircraft landings (see the section on Interstate trivia below).

One potential civil defense use of the Interstate Highway System is for the emergency evacuation of cities in the event of a potential nuclear war. The Interstate Highway System has been used to facilitate evacuations in the face of hurricanes and other natural disasters. An option for maximizing throughput is to reverse the flow of traffic on one side so that all lanes become outbound lanes. This procedure, known as Contraflow, was employed in 2005 in the evacuations of New Orleans, Louisiana and Houston, Texas prior to hurricanes Katrina and Rita, respectively. Several Interstates in the South, including I-16 in Georgia, I-40 in North Carolina, I-65 in Alabama, I-10, I-12, I-55 & I-59 in Louisiana, and I-55 & I-59 in Mississippi, are equipped and signed specifically for contraflow, with crossovers inland after major interchanges to distribute much of the traffic. (This is however not limited to Interstates; State Road 528 in Central Florida has the same setup.)

[edit] Terminology

While the name implies that Interstate highways cross state lines, many do not.^[4] Rather, they are funded federally with money shared between the states. There are interstate highways in Hawaii, funded in the same way as in the other states, but entirely within the populous island of Oahu. They have the designation of H-X and connect military bases. Similarly, both Alaska and Puerto Rico have public roads that receive funding from the Interstate program, though these routes are not signed as Interstate Highways except "on paper".

[edit] Primary routes

See also: List of Interstate Highways

Interstate highways are typically known as Interstate XX or I-XX, where "XX" is the two-digit route number; sometimes Interstate Highway XX (IH XX) or Interstate Route XX (IR XX) is used. In some areas, the more generic Route XX or Highway XX is used.

The numbering scheme for the Interstate Highway System (as well as the U.S. Highway System) is coordinated by the American Association of State Highway and Transportation Officials (AASHTO), though their authority is occasionally trumped by a number written into Federal law. Within the continental United States, primary Interstates (also called main line Interstates or two-digit Interstates) are given one- or two-digit route numbers. Most Interstates have two numbers; there are only three one-digit Interstates in the system: I-4, I-5 and I-8. Within this category, east-west highways are assigned even numbers, and north-south highways are assigned odd numbers. Odd route numbers increase from west to east, and even numbered routes increase from south to north. An exception of this is the fact that I-75 is to the east of I-85 south of Atlanta. This is not so north of Atlanta. Numbers divisible by 5 are intended to be major among the primary routes, carrying traffic long distances. For example, I-5 runs from Canada to Mexico along the west coast (the only interstate to do so) while I-95 runs from Miami north to Canada. In addition, I-10 runs from Santa Monica, California to Jacksonville, Florida while I-90 runs from Seattle to Boston. However, not all primary routes divisible by 5 traverse long distances. I-45 runs from Galveston, Texas north to Dallas, Texas, a distance of only 284 miles. It is the only primary route divisible by 5 that does not cross state lines. See List of intrastate Interstate Highways for other primary routes that do not cross state lines.

It should be noted that I-50 and I-60 do not exist (and there are no even-numbered Interstates from 46 to 62), mainly because they would most likely have passed through the same states that already have US 50 and US 60. AASHTO rules discourage Interstate and US Highways having the same number within the same state, although I-24 and US 24 exist at opposite ends of Illinois. Some planned Interstates do not follow this guideline — I-69 will intersect US 69 in Lufkin, Texas^[5], I-74 will overlap US 74 in North Carolina, and I-41 will do the same with US 41 in Wisconsin.

Several two-digit numbers are shared between two roads at opposite ends of the country, namely I-76, I-84, I-86 and I-88. Some of these were the result of a change in the numbering system in the 1970s; previously letter-suffixed numbers were used for long spurs off primary routes; for example, western I-84 was I-80N, as it went north from I-80. In the 1970s, AASHTO decided to eliminate these; some became additional two-digit routes, while others became three-digit routes (see below). Only two pairs of these exist; I-35 splits into I-35W and I-35E through both the Dallas-Fort Worth and the Minneapolis-St. Paul areas.

For the sake of efficiency, some Interstates double up for short or sometimes long distances. This is usually referred to as a concurrency. One example is where I-75 and I-85 combine just below downtown Atlanta to form the Downtown Connector, a major thoroughfare through the city. Another example is the merging and diverging of Interstates I-90 and I-94, which double and then separate several times across the upper Midwest and Great Plains. I-90 and I-94 even join with I-39 from Madison, WI, to Portage, WI, creating the longest such trifecta in the Interstate system. A recent addition is the I-73/I-74 duplex, which runs along U.S. Route 220 from Asheboro, North Carolina to Rockingham, North Carolina. I-73 will also share routes with I-40 and I-85 on the Greensboro Urban Loop, a new bypass route around Greensboro, North Carolina. Strict adherence to the directional nature of the system results in some amusing oddities. For a nine-mile stretch east of Wytheville, Virginia, the driver can be traveling on both I-81 North and I-77 South at the same time (and vice versa) (see also Wrong-way concurrency).

[edit] Three-digit Interstates

See also: List of auxiliary Interstate Highways

Auxiliary Interstate Highways are given three-digit route numbers, which consist of a single digit prefixed to the two-digit number of a primary Interstate highway, to designate spur or loop routes branching from either the primary route or one of its other auxiliary routes. A spur route is one that deviates from its parent and does not end at another Interstate; it is given an odd first digit. A loop route is one that returns to its parent; it is given an even first digit. The number given to the first digit of a route that branches from the parent to end at another Interstate depends on the state; some consider these routes spurs and assign odd first digits, while others consider them loop connectors giving them even first digits.

When letter-suffixed two-digit Interstates (see above) were in abundance, their auxiliary routes were given a number without a letter suffix.

Due to the large number of these routes, auxiliary route numbers may be repeated in different states along the mainline; but no two three-digit Interstates in the same state can share a number. For instance, I-90 in New York alone has a full set of three-digit Interstates - I-190, I-290, I-390, I-490, I-590, I-690, I-790, I-890 and I-990.

Closed loops usually retain a single designation for the entire route, even when they enter other states. For example, Cincinnati, like many other cities, features a large loop around the city that intersects with the primary routes I-71, I-74, and I-75 and travels through Ohio, Kentucky, and Indiana. The entire 84-mile loop is labeled I-275. (It is also the only three-digit interstate to ever go through three states.)

Also, the loop highway around Washington, D.C., known as the Capital Beltway, carries both I-95 and I-495. Originally, the loop carried only I-495, in anticipation of I-95 being routed through Washington, but in 1977, I-95 was rerouted on the eastern half of the loop due to the cancellation of the segment that would have connected downtown Washington to College Park, Maryland, while I-495 remained on the western half. I-495 was added back to the eastern half of the loop in 1989, creating a rare concurrency of primary and auxiliary routes. Another example of such a concurrency is that of I-40 and I-440 in Raleigh, North Carolina.

Of course, there are exceptions to these guidelines:

• A contiguous loop surrounds the entire Minneapolis-St. Paul Metro area. I-94 intersects the loop in two spots and runs directly through it separating it into southern and northern halves; the southern half of it is labeled I-494 while the northern half of it is labeled I-694.
• I-270 and I-255 form a beltway around the greater St. Louis area. On its southwest corner, I-270 becomes I-255 as it crosses I-55 counter-clockwise only to terminate back at I-270 in the northeast. In the early 1980's, local residents stopped a plan to designate the entire closed loop as I-270 and renumber the stub of I-270 from Glen Carbon to Edwardsville to I-870.
• New York City has numerous spur routes off from I-78 and I-95, but none of I-78's spur routes actually intersect with I-78.
• An auxiliary route numbered I-238 connects San Leandro and Castro Valley, California, yet there is no I-38. Instead, I-238 carries the designation of the portion of State Route 238 that the Interstate designation replaced.
• Even the suffix route rule had an exception, present day I-184 in Idaho used to be I-180N.

[edit] Exceptions

Interstate 238 near Oakland, California is one of two major exceptions to the numbering scheme, as no Interstate 38 exists. This number exists because Interstate 238 replaced a segment of State Route 238, and no appropriate number derived from the parent, I-80, was available. The other exception is Interstate 99 in Pennsylvania, which was written into law as I-99 by Pennsylvania Congressman Bud Shuster; I-99 (which is also U.S. Route 220) is west of several Interstates that are numerically less than 99, but 99 was the nearest odd 2-digit number available for the interstate.

A less-notable exception is I-82, which lies fully north of I-84; this is a relic from I-84 previously having the designation of I-80N.

Some Proposed Interstate Highways have been given similarly non-conforming designations by their legislative proponents. For example, backers of the proposed Third Infantry Division Highway, a route in Georgia and Tennessee, have suggested it be named Interstate 3, in honor of the division for which the highway is named.

[edit] Other notable examples

The following two-digit Interstates change signed direction from their normal (even=east-west, odd=north-south) direction:

• I-69 east of Lansing, Michigan
• I-76 in Nebraska

The I-69 segment is an extension of its original route; I-76 only runs for two miles in Nebraska before ending at I-80.

Two-digit Interstates in Hawaii, as well as the "paper" Interstates of Alaska and Puerto Rico, are numbered sequentially in order of funding, without regard to the rules on odd and even numbers.

Business Loop and Business Spur Interstates are not subject to any of the Interstate Highway standards. Their designation is simple - a Business Loop heads into a downtown area from its parent and returns to its parent; a Business Spur ends downtown, occasionally continuing from the end of the main Interstate. Business routes can split from either two- or three-digit Interstates, and can be repeated within a state. In a few cases, where an Interstate has been realigned, the old road has been designated a Business Loop because it is not up to standards.

[edit] Financing

About 56%^[6] of the construction and maintenance costs are funded through user fees, primarily gasoline taxes, collected by states and the federal government, and tolls collected on toll roads and bridges. The rest of the costs are borne by the federal budget. In the eastern United States, large sections of some Interstate Highways planned or built prior to 1956 are operated as toll roads. The taxes dedicated to the construction and maintenance of highways are often criticized as a direct subsidy from the government to promote and maintain auto-oriented development as we know it today.

As American suburbs push ever outward, the costs incurred of maintaining freeway infrastructure has started to catch up with the economy, leaving little in the way of funds for new interstate construction ^[7]. This has led to the proliferation of the toll road (turnpike) as the new method of building limited-access highways in suburban areas. Also, some interstates are being privately maintained now (VMS in Texas, I-35) in order to cut rising costs of maintenance and allow state departments of transportation to focus on serving the fastest growing regions in their respective states. The future of the interstate system as we know it is in question. It is entirely possible that parts of the system will have to be tolled in the future to meet maintenance and expansion demands, as is done with adding toll HOV/HOT lanes in certain cities like San Diego, Minneapolis, Houston, Dallas, Atlanta and Washington, D.C.

[edit] The federal role in financing

The dominant role of the federal government in road finance has enabled it to achieve legislative goals that fall outside its power to regulate interstate commerce as enumerated in the federal Constitution. By threatening to withhold highway funds, the federal government has been able to stimulate state legislatures to pass a variety of laws. Although some object on the ground that this infringes on states' rights, the Supreme Court has upheld the practice as a permissible use of the Constitution's Commerce Clause.

The first major example was the introduction of the 55 mph (90 km/h) national speed limit in 1974. While its purpose was to save fuel in the wake of the 1973 energy crisis, federal speed controls stayed in effect for 21 years. The initial acceptance of the national speed limit emboldened various presidents and Congresses to enact additional pieces of legislation, some of which have nothing to do with highways or transportation. Examples include:

• Increasing the legal drinking age to 21.
• Megan's Law legislation, requring states to disclose identities of sex offenders.
• Lowering the legal intoxication level to 0.08%.

States must also meet minimum enforcement standards for all federally mandated legislation (for example, minimum penalties for violation of these laws and a minimum number of per capita underage drinking convictions or a compelling explanation regarding why this number is not met). This has proved to be controversial. Supporters hold that it is a way to provide an impetus to states to pass uniform legislation. Critics maintain that using highway dollars in this fashion upsets the balance between federal and states rights in favor of the federal government, and effectively holds funds as ransom in order to coerce state governments into passing laws that would not have otherwise been introduced. Some have even argued that the current arrangement is unconstitutional. Law enforcement agencies in some states argue that efforts to meet quotas for underage drinking convictions have distracted them from other matters and strained relations with those under 21. Any state that were to lose federal highway funding would quickly face deteriorating infrastructure, fiscal impoverishment, or both.

Of course, a state which lost federal highway funding could theoretically threaten to stop maintaining its highways, if that were politically palatable to its residents.

[edit] Non-chargeable Interstate routes

In addition to Interstate highways financed with federal funds (Chargeable Interstate routes), federal laws allow other highways to be signed as Interstates, if they meet the Interstate Highway standards and are logical additions or connections to the System.

Called Non-Chargeable Interstate routes, these additions fall under two categories:

1. Routes that already meet Interstate standards. These may immediately be signed as Interstates once their proposed number is approved, or may be retained with a non-Interstate designation.
2. Routes not yet upgraded to Interstate standards. These cannot be signed as Interstates until they have been fully upgraded.

[edit] Signage

Interstate 95 shield

Interstate Highways are signed by a number on a red, white and blue sign as shown to the right. In the original design, the state was listed above the highway number, but in many states, this area is now left blank (US Highway Shields also had the same setup through time). The sign itself measures 36 inches high (91 cm) , and is 36 inches (91 cm) wide for two-digit interstates, or 45 inches (114 cm) for three-digit interstates.

Business Loop and Business Spur Interstates use a special shield where the red and blue are replaced with green; the word BUSINESS appears instead of INTERSTATE, and the word SPUR or LOOP usually appears above the number.

The majority of Interstates have exit numbers. All traffic signs and lane markings on the Interstates are supposed to be designed in compliance with the Manual on Uniform Traffic Control Devices (MUTCD). However, there are many local and regional variations in signage.

For many years, California was the only state that did not use an exit numbering system. It was granted an exemption in the 1950s due to having an already largely completed and signed highway system; at the time, placing exit number signage on the signs across the state was deemed to be too expensive. Since 2002, however, California has begun to incorporate exit numbers on all of its freeways - interstate, U.S., and state routes alike. To mitigate costs, a common occurrence is for CalTrans to install exit number signage only when a freeway or interchange is built, reconstructed, retrofitted, or repaired. It should be noted, however, that the majority of the exits along Interstates 5, 10, and 80 now have exit number signage, particularly in rural areas.

In most states, the exit numbers correspond to the mileage markers on the Interstates (with an exception being I-19 in Arizona, whose length is measured in kilometers instead of miles). Many northeastern states label exit numbers sequentially, regardless of how many miles have passed between exits. Maine, Georgia, Pennsylvania, Virginia, and Florida followed this system for a number of years, but recently converted to having the exit numbers correspond to mileage markers. On even-numbered Interstates, mileage increases to the east and decreases to the west (except on the I-90 portion of the New York State Thruway, the I-190 spur into O'Hare International Airport in Chicago, and the portion of I-76 in New Jersey, all of which count up going west); and on odd-numbered Interstates, mileage increases to the north and decreases to the south. In both cases, the exit numbers increase and decrease accordingly.

States still numbering sequentially are: Connecticut, Delaware, Massachusetts, New Hampshire, New York, Rhode Island and Vermont. The New Jersey Turnpike also has sequential numbering, but other interstates within New Jersey generally use mile markers.

[edit] Trivia

• Alaska and Puerto Rico have roads designated as Interstates for funding purposes but which are neither planned for or currently built to Interstate Highway standards. The public controlled-access highways of Puerto Rico are the Autopistas (PR-22, PR-52, and PR-53).
• A widespread urban legend states that one out of every five miles of the Interstate Highway System must be built straight and flat so as to be usable by aircraft during times of war; it is not true.^[8]
• Several interstate highways have buildings over the highway, using air rights.

Further information: List of structures built on top of interstates

• Although overhead signs are supposed to list the next control city, there are numerous exceptions.

Further information: List of long-distance mileage signs on interstates

• Most Interstates are maintained by the states or toll authorities. The Woodrow Wilson Bridge, part of Interstate 95 and Interstate 495, is maintained by the federal government. A few Interstates are maintained by local authorities:
  • Baltimore, Maryland: Interstate 70 and Interstate 83 in the city limits^[9]
  • New York City: Small portions of Interstate 278^[10]
  • Washington, D.C.: As the city and district are identical, the district maintains the portions of Interstate 66, Interstate 295, Interstate 395 and Interstate 695 inside the city.
• The only concurrency of two auxiliary routes is Interstate 271 and Interstate 480 near Cleveland, Ohio.
• All but five state capitals are directly served by the Interstate System. Carson City, Nevada; Dover, Delaware; Jefferson City, Missouri; Juneau, Alaska; and Pierre, South Dakota are not, though this will change once the Interstate 580 between Reno, Nevada and Carson City is completed.
• The Interstate System has a few gaps that violate the Interstate Highway standards and AASHTO rules.
• The most heavily traveled area of the Interstate Highway system is the 405 Freeway in Seal Beach, California, with a 2002 estimate of 377,000 vehicles a day. The least traveled section is Interstate 95 just north of Houlton, Maine (near the Canadian border), with 1,880 vehicles a day (2001 estimate).

[edit] Criticism

John Steinbeck, in his travelogue Travels With Charley, claimed "When we get these thruways across the whole country, as we will and must, it will be possible to drive from New York to California without seeing a single thing." Charles Kuralt echoed this statement in his biography A Life on the Road: "The interstate highway system is a wonderful thing. It makes it possible to go from coast to coast without seeing anything or meeting anybody. If the United States interests you, stay off the interstates." These quotes reference the tendency of Interstate highways to emphasize more rapid, uninterrupted transportation than other road networks. This could be contrasted to the sometimes romanticized perception of state and county routes, often two-lane highways, that may offer more chances to stop at local small businesses or see true rural America.

[edit] References

[edit] See also

edit Main Interstate Highways (major in pink)
4	5	8	10	12	15	16	17	19	20	22	24	25	26	27	29
30	35	37	39	40	43	44	45	49	55	57	59	64	65	66
66 (W)		68	69	70	71	72	73	74	75	76 (W)		76 (E)		77	78
79	80	81	82	83	84 (W)		84 (E)		85	86 (W)		86 (E)		87
88 (W)		88 (E)		89	90	91	93	94	95	96	97	99	(238)
H-1	H-2	H-3
Unsigned			A-1	A-2	A-3	A-4	PRI-1		PRI-2		PRI-3
Lists		Main - Auxiliary - Suffixed - Business - Proposed - Unsigned Gaps - Intrastate - Interstate standards - Replaced

• Contraflow
• Gas tax
• Highway patrol
• Non-motorized vehicle access on freeways
• List of roads and highways
• Mile-log
• Parkway
• List of major freeway systems
• Interstate Highway System chronology
• Adopt a Highway

[edit] External links

Wikimedia Commons has media related to:

Category:Interstate Highways

• Interstate Highway information
• FHWA Route Log and Finder List
• FHWA Turner-Fairbank Highway Research Center - Analysis and History of Interstate Highway System
• History of urban interstates - Norton, "Fighting Traffic: U.S. Transportation Policy and Urban Congestion, 1955-1970"
• 3-digit Interstate Highways
• Pictures of all Interstates
• One of 100 milestone documents of American history
• Federal Highway Administration's article on the act
• Fortune magazine on history of the Interstate Highway System
• Tony Graham's Exit List Collection A compilation of all Interstate exit lists available online
• Another great Interstate Page, with facts on all 2-digit Interstates and links to their exit lists
• Highway Heaven Contains exit lists for most Interstate highways
• RoadGeek - A complete set of TrueType fonts for simulating Interstate and other highway signage
• 2006: 50th Aniversary of the Interstate Highway System Celebration - from the American Road & Transportation Builders Association
• Interstate50th.org - A website that celebrates the system's golden anniversary, filled with facts and other interesting information about the highways, such as where the first miles of Interstate were built