Encyclopedia
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 . This system is equivalent to the
motorway system of the
Republic of Ireland, the
United Kingdom, and many members of the
Commonwealth of Nations.
While Interstate Highways usually receive substantial federal funding and comply to 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 .
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; of these trips, about one-third utilize the Interstate system.
History
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.
Although construction on the Interstate Highway system continues, it was officially regarded as complete in 1991 . The initial cost estimate for the system was $25 billion over twelve years; it ended up costing $114 billion, taking 35 years to complete .
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 plans to be completed . Several other routes have non-
freeway sections , but are considered to be complete.
Missouri and Kansas have laid claims that
I-70 in those states was the first interstate . 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.
Standards
- Main article: Interstate Highway standards
The
American Association of State Highway and Transportation Officials has defined a set of standards that all new Interstates must meet unless a waiver from the Federal Highway Administration 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 are limited to toll booths and
ramp meters .
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 85 mph 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 across the country.
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 .
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.
Terminology
While the name implies that Interstate highways cross
state lines, many do not. 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".
Primary routes
Interstate highways are typically known as
Interstate XX or
I-XX, where "XX" is the two-digit route number; sometimes
Interstate Highway XX or
Interstate Route XX is used. In some areas, the more generic
Route XX or
Highway XX is used.
The numbering scheme for the Interstate Highway System is coordinated by the
American Association of State Highway and Transportation Officials , though their authority is occasionally trumped by a number written into Federal law. Within the continental United States, primary 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 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 , 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,
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 . 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. 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 .
Three-digit Interstates
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 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.
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 of 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.
- Even the suffix route rule had an exception, present day I-184 in Idaho used to be I-180N.
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 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.
Other notable examples
The following two-digit Interstates change signed direction from their normal direction:
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.
Financing
About 56% 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 . This has led to the proliferation of the toll road as the new method of building limited-access highways in suburban areas. Also, some interstates are being privately maintained now 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, and
Washington, D.C.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
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 . 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.
Non-chargeable Interstate routes
In addition to Interstate highways financed with federal funds , 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:
- 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.
- Routes not yet upgraded to Interstate standards. These cannot be signed as Interstates until they have been fully upgraded.
Signage
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 . The sign itself measures 36 inches high , and is 36 inches wide for two-digit interstates, or 45 inches 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 . 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 . 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 ; 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.
Trivia
