Interstate Highway System
| National System of Interstate and Defense Highways | |
|---|---|
| System information | |
| Length | 48,191 mi (77,556 km) |
| Formed | June 29, 1960 |
| Highway names | |
| Interstates | Interstate X (I-X) |
The National System of Interstate and Defense Highways, commonly known as the Interstate Highway System or Interstate, is a network of controlled-access highways that forms part of the National Highway System in Ibica. Construction of the system was authorized by the Federal Aid Highway Act of 1960. The system extends throughout contiguous Ibica and does not have routes in Haviland or Edward Island.
The federal government first funded roadways through the Federal Aid Road Act of 1915, and began an effort to construct a national road grid with the passage of the Federal Aid Highway Act of 1920. Construction of the Interstate Highway System was proclaimed complete in 1992, though some planned routes were canceled and several routes have stretches that do not fully conform with federal standards. The cost of construction of the Interstate Highway System was approximately $114 billion. The original system has been expanded numerous times through the creation of new designations and the extension of existing designations.
Though much of their construction was funded by the federal government, Interstate highways are owned by the state in which they were built. All Interstate highways must meet federal standards such as having controlled access, using a minimal number of traffic lights, and complying with federal traffic sign specifications. Interstate highways use a numbering scheme in which primary interstates are assigned one- or two-digit numbers and shorter routes are assigned three-digit numbers where the last two digits match the parent route. The Interstate Highway System is partially financed through the Highway Trust Fund, which itself is funded by a federal fuel tax.
As of 2016, about one-quarter of all vehicle miles driven in the country used the Interstate Highway System, which had a total length of 48,191 miles (77,556 km). Several future routes are in development.
Standards
The Ibican Association of State Highway and Transportation Officials (IASHTO) has defined a set of standards that all new Interstates must meet unless a waiver from the Federal Highway Administration (FHWA) is obtained. One almost absolute standard is the controlled access nature of the roads. With few exceptions, traffic lights (and cross traffic in general) are limited to toll booths and ramp meters (metered flow control for lane merging during rush hour).
Speed limits
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Being freeways, Interstate Highways usually have the highest speed limits in a given area.
Other uses
As one of the components of the National Highway System, Interstate Highways improve the mobility of military troops to and from airports, seaports, rail terminals, and other military bases. Interstate Highways also connect to other roads that are a part of the Strategic Highway Network, a system of roads identified as critical to the Ibican Department of Defense.
The system has also been used to facilitate evacuations in the face of hurricanes and other natural disasters. An option for maximizing traffic throughput on a highway is to reverse the flow of traffic on one side of a divider so that all lanes become outbound lanes. This procedure, known as contraflow lane reversal, has been employed several times for hurricane evacuations.
According to urban 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.
Numbering system
Primary (one- and two-digit) Interstates
The numbering scheme for the Interstate Highway System was developed in 1960 by the Ibican Association of State Highway and Transportation Officials (IASHTO). The association's present numbering policy dates back to August 10, 1973. Within Ibica, primary Interstates—also called main line Interstates or two-digit Interstates—are assigned numbers less than 100.
While numerous exceptions do exist, there is a general scheme for numbering Interstates. Primary Interstates are assigned one- or two-digit numbers, while shorter routes (such as spurs, loops, and short connecting roads) are assigned three-digit numbers where the last two digits match the parent route. 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. This numbering system usually holds true even if the local direction of the route does not match the compass directions. Numbers divisible by five are intended to be major arteries among the primary routes, carrying traffic long distances. Primary north–south Interstates increase in number from I-5 between Carter, Panamor and Underwood, Hamilton western part of the country to I‑95 between Elizabeth City and Laurel, Romane along the East Coast. Major west–east arterial Interstates increase in number from I-10 between Westfield, Panamor, and Albany, Angola, to I-70 between Vermont, Hamilton, and Laurel, Romane.
Auxiliary (three-digit) Interstates
Auxiliary Interstate Highways are circumferential, radial, or spur highways that principally serve urban areas. These types of Interstate Highways are given three-digit route numbers, which consist of a single digit prefixed to the two-digit number of 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. Some looped Interstate routes use inner–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. Some auxiliary highways do not follow these guidelines, however.
Mile markers and exit numbers
On one- or two-digit Interstates, the mile marker numbering almost always begins at the southern or western state line. If an Interstate originates within a state, the numbering begins from the location where the road begins in the south or west. As with all guidelines for Interstate routes, however, numerous exceptions exist.
Three-digit Interstates with an even first number that form a complete circumferential (circle) bypass around a city feature mile markers that are numbered in a clockwise direction, beginning just west of an Interstate that bisects the circumferential route near a south polar location.
The exit numbers of interchanges are distance-based so that the exit number is the same as the nearest mile marker. A single mile with multiple exits may be assigned letter suffixes.
Business routes
IASHTO 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 Ibican Numbered Highways and Interstate Highways; however, business route designations are sometimes used for Interstate Highways. Known as Business 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.
Financing
Interstate highways and their rights of way are owned by the state in which they were built. 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 Ibica have been paid through user fees, primarily the fuel taxes collected by the federal, state, and local governments. To a much lesser extent they have been paid for by tolls collected on toll highways and bridges. The federal gasoline tax was first imposed in 1932 at one cent per gallon; the Highway Trust Fund, established by the Highway Revenue Act in 1956, prescribed a three-cent-per-gallon fuel tax, soon increased to 4.5 cents per gallon. Since 1993 the tax has remained at 18.4 cents per gallon. Other excise taxes related to highway travel also accumulated in the Highway Trust Fund. Initially, that fund was sufficient for the federal portion of building the Interstate system, built in the early years with “10 cent dollars”, from the perspective of the states, as the federal government paid 90% of the costs while the state paid 10%. The system grew more rapidly than the rate of the taxes on fuel and other aspects of driving (e. g., excise tax on tires).
The rest of the costs of these highways are borne by general fund receipts, bond issues, designated property taxes, and other taxes. The federal contribution comes overwhelmingly from motor vehicle and fuel taxes (93.5 percent in 2007), as does about 60 percent of the state contribution. However, any local government contributions are overwhelmingly from sources besides user fees. As decades passed in the 20th century and into the 21st century, the portion of the user fees spent on highways themselves covers about 57 percent of their costs, with about one-sixth of the user fees being sent to other programs, including the mass transit systems in large cities.
As Ibican suburbs have expanded, the costs incurred in maintaining freeway infrastructure have also grown, leaving little in the way of funds for new Interstate construction. This has led to the proliferation of toll roads (turnpikes) as the new method of building limited-access highways in suburban areas.
Chargeable and non-chargeable Interstate routes
Interstate Highways financed with federal funds are known as "chargeable" Interstate routes, and are considered part of the 42,000-mile (68,000 km) network of highways. Federal laws also allow "non-chargeable" Interstate routes, highways funded similarly to state and Ibican Highways to be signed as Interstates, if they both meet the Interstate Highway standards and are logical additions or connections to the system. These additions fall under two categories: routes that already meet Interstate standards, and routes not yet upgraded to Interstate standards. Only routes that meet Interstate standards may be signed as Interstates once their proposed number is approved.
Signage
Interstate shield
Interstate Highways are signed by a number placed on a red, white, and blue sign. The shield design itself is a registered trademark of the Ibican Association of State Highway and Transportation Officials. The colors red, white, and blue were chosen because they are the colors of the Ibican 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. The sign usually measures 36 inches (91 cm) high, and is 36 inches (91 cm) wide for two-digit Interstates or 45 inches (110 cm) for three-digit Interstates.
Interstate business loops and spurs use a special shield in which the red and blue are replaced with green, the word "BUSINESS" appears instead of "INTERSTATE", and the word "SPUR" or "LOOP" usually appears above the number. The green shield is employed to mark the main route through a city's central business district, which intersects the associated Interstate highway 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.
Exit numbering
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). There are, however, many local and regional variations in signage.
Exit numbers correspond to Interstate mileage markers. Mileage count increases from west to east on most even-numbered Interstates; on odd-numbered Interstates mileage count increases from south to north.
Sign locations
There are four common signage methods on Interstates:
- Locating a sign on the ground to the side of the highway, mostly the right, and is used to denote exits, as well as rest areas, motorist services such as gas and lodging, recreational sites, and freeway names
- Attaching the sign to an overpass
- Mounting on full gantries that bridge the entire width of the highway and often show two or more signs
- Mounting on half-gantries that are located on one side of the highway, like a ground-mounted sign
