A freeway — also known as a highway, superhighway, autoroute, autobahn, autopista, autovía, autostrada, autosnelweg (Netherlands), dual carriageway, expressway, or motorway — is a type of road designed for safer high-speed operation of motor vehicles through the elimination of at-grade intersections. This is accomplished by preventing access to and from adjacent properties and eliminating all cross traffic through the use of grade separations and interchanges; railroad crossings are also removed. Such highways are usually divided with at least two lanes in each direction. Because traffic never crosses at-grade, there are generally no traffic lights or stop signs.
The word freeway first surfaced in the mid-1930s in proposals for the improvement of the New York City parkway network. It is currently in regular use in the United States as well as parts of Canada and Australia. Other countries refer to a freeway as a grade-separated highway or a superhighway.
In the United States, the term freeway is frequently used. In some regions of the U.S., other terms are also used, including Interstate, highway, expressway, and turnpike. While some people use these terms interchangeably, turnpikes and thruways have specific associations with toll roads and other limited access highways, such as the Pennsylvania Turnpike, West Virginia Turnpike, New Jersey Turnpike, Florida's Turnpike, and New York State Thruway; consequently, the term freeway is often used in contrast to refer only to a toll-free road as opposed to its original meaning – in which the component "free" implied freedom from traffic interference rather than "at no cost" – still used in other countries and in parts of the U.S.
Freeways, by definition, have no at-grade intersections with other roads, railroads or multi-use trails. Movable bridges, such as the Interstate Bridge on I-5 between Oregon and Washington, may require drivers to yield to cross traffic on the river. Not all roads bearing the name of freeway are in fact freeways by definition; for example, the William L. Wilson Freeway (U.S. Route 340) by Harpers Ferry, West Virginia, is a two-lane undivided roadway featuring at-grade intersections.
The crossing of freeways by other routes is typically achieved with grade separation either in the form of underpasses or overpasses. In addition to sidewalks (footpaths) attached to roads that cross a freeway, specialized pedestrian bridges or tunnels may also be provided. These structures enable pedestrians and cyclists to cross the freeway at that point without a detour to the nearest road crossing.
Access to freeways is typically provided only at grade-separated interchanges, though lower-standard right-in/right-out access can be used for direct connections to side roads. In many cases, sophisticated interchanges allow for smooth, uninterrupted transitions between intersecting freeways and busy arterial roads. However, sometimes it is necessary to exit onto a surface road to transfer from one freeway to another. An example of this would be Interstate 70 in the town of Breezewood, Pennsylvania.
Speed limits are generally higher on freeways, and are occasionally nonexistent (as on much of Germany's Autobahn network). Because higher speeds reduce decision time, freeways are usually equipped with a larger number of guide signs than other roads, and the signs themselves are physically larger. Guide signs are often mounted on overpasses or overhead gantries so that drivers can see where each lane goes. Exit numbers are commonly derived from the exit's distance in miles or kilometers from the start of the freeway. In some areas, there are public rest areas or service areas on freeways, as well as emergency phones on the shoulder at regular intervals.
In the United States, mileposts start at the southern or westernmost point on the freeway (either its terminus or the state line). California, Ohio, and Nevada uses a postmile system where markers indicate mileage through the state's individual counties; however, Nevada and Ohio also use the standard milepost system concurrently with their respective postmile systems on freeways only. Until the 1980s, New York used reference markers which, like California, indicated mileage through individual counties. The New York State Department of Transportation has since supplemented their reference marker system with mileposts indicating a freeway's mileage through the state.
Two-lane freeways, often undivided, are sometimes built when traffic volumes are low or right-of-way is limited; they may be designed for easy conversion to one side of a four-lane freeway. Otherwise, freeways typically have at least two lanes in each direction; some busy ones can have as many as 16 or more lanes in total.
In Mississauga, Ontario, Highway 401 uses collector-express lanes for a total of 18 lanes through its intersection with 403/410 and 427. In San Diego, California, Interstate 5 has a similar system of express and local lanes for a maximum width of 21 lanes on a two-mile segment between Interstate 805 and California State Route 56.
These wide freeways may use separate collector and express lanes to separate through traffic from local traffic, or special high-occupancy vehicle lanes, either as a special restriction on the innermost lane or a separate roadway, to encourage carpooling. These HOV lanes, or roadways open to all traffic, can be reversible lanes, providing more capacity in the direction of heavy traffic, and reversing direction before traffic switches. Sometimes a collector/distributor road, a shorter version of a local lane, shifts weaving between closely-spaced interchanges to a separate roadway or altogether eliminates it.
In some parts of the world, notably Texas, frontage roads form an integral part of the freeway system. These parallel surface roads typically run the entire length of the freeway and provide a transition between high-speed "through" traffic and local traffic. Frequent on- and off-ramps provide access from the freeway to the frontage road, which in turn provides direct access to local roads and businesses.
Except on some two-lane freeways (and very rarely on wider freeways), a median separates the opposite directions of traffic. This strip may be as simple as a grassy area, or may include a crash barrier such as a "Jersey barrier" or a "Ontario Tall Wall"" to prevent head-on collisions. On some freeways, the two carriageways are built on different alignments; this may be done to make use of available corridors in a mountainous area or to provide narrower corridors through dense urban areas.
Some roads in Ohio that conform to freeway criteria use at-grade intersections in lieu of over/under-passes, with occasional interchanges to avoid signalized traffic interruption (i.e., traffic lights are omitted). Examples include US-23 between OH-15's eastern terminus and Delaware, Ohio, along with highway 15 between its eastern terminus and I-75, US-30, OH-29/US-33, and US-35 in western and central Ohio. These roads are fundamentally expressways, but expressways tend to have lower design speeds, and signalized at-grade intersections.
To reduce the probability that high-speed freeway traffic will have to slow down for slower same-direction traffic, access to freeways is usually limited to drivers of motor vehicles which are powerful enough to maintain a certain minimum speed. Some East Asian countries partially restrict the use of motorcycles or ban them completely from freeways (or expressways in countries where that term is used) (see restrictions on motorcycle use on freeways).
Travelers in a low-powered transportation class (such as pedestrian, bicyclist, equestrian, and moped driver) are banned at all times from the freeways in many areas by default. In some jurisdictions, these classes are allowed on the shoulders of certain freeways (usually where the freeway completely replaced an existing road) or on sidepaths.
In the United States, a "freeway" is defined by the federal government’s Manual on Uniform Traffic Control Devices as a divided highway with full control of access. This means two things. Adjoining property owners do not have a legal right of access, meaning that they cannot connect their lands to the highway by constructing driveways, although frontage roads provide access to properties adjacent to a freeway in many places. When an existing road is converted into a freeway, all existing driveways must be removed and access to adjacent private lands must be blocked with fences or walls. Traffic on the highway is "free-flowing". All cross-traffic (and left-turning traffic) has been relegated to overpasses or underpasses, so that there are no traffic conflicts on the main line of the highway which must be regulated by a traffic light, stop signs, or other traffic control devices. Achieving such free flow requires the construction of many bridges, tunnels, and ramp systems. The advantage of grade-separated interchanges is that freeway drivers can almost always maintain their speed at junctions since they do not need to yield to crossing traffic.
In contrast, an expressway is defined as a divided highway with partial control of access. Expressways may have driveways and at-grade intersections, though these are usually less numerous than on ordinary arterial roads.
This distinction was apparently first developed in 1949 by the Special Committee on Nomenclature of what is now the American Association of State Highway and Transportation Officials. In turn, the definitions were incorporated into AASHTO's official standards book, the Manual on Uniform Traffic Control Devices, which would become the national standards book of the U.S. Department of Transportation under a 1966 federal statute. The same distinction has also been codified into the statutory law of seven states: California, Mississippi, Missouri, Nebraska, North Dakota, Ohio, and Wisconsin. However, each state codified the federal distinction slightly differently. California expressways do not necessarily have to be divided, though they must have at least partial access control. For both terms to apply, in Wisconsin, a divided highway must be at least four lanes wide; and in Missouri, both terms apply only to divided highways at least long that are not part of the Interstate Highway System. In North Dakota and Mississippi, an expressway may have "full or partial" access control and "generally" has grade separations at intersections; a freeway is then defined as an expressway with full access control. Ohio's statute is similar, but instead of the vague word generally, it imposes a requirement that 50% of an expressway's intersections must be grade-separated for the term to apply.
The term expressway is also used for what the federal government calls "freeways"; see the expressway article for further information. Where the terms are distinguished, all freeways are expressways, while not all expressways are freeways.
Freeways have been constructed both between urban centers and within them, leading to the sprawling suburban development found near most modern cities. Freeways reduced travel times and accident rates, though the higher speeds have increased the severity and death rates of the collisions that do occur.
Freeways have been heavily criticized by environmentalists, urbanists, and preservationists for the noise, pollution, and economic shifts they bring. Additionally, they have also been criticized by the driving public for the inefficiency with which they handle peak hour traffic.
Often, rural freeways open up vast areas to economic development, generally raising property values. In contrast to this, above ground freeways in urban areas are often a source of lowered property values, contributing to urban decay. Even with overpasses and underpasses, above ground freeways divide neighborhoods — especially impoverished ones where residents are less likely to own a car, or to have the political and economic influence to resist construction efforts. Beginning in the early 1970s, the U.S. Congress identified freeways and other urban highways as responsible for most of the noise exposure of the U.S. population. Subsequently, computer models were developed to analyze freeway noise and aid in their siting and design to minimize noise exposure. Some freeways have even been demolished and reclaimed as boulevards, notably in Portland (Harbor Drive), New York City (West Side Highway), Boston (Central Artery), San Francisco (Embarcadero Freeway) and Milwaukee (Park East Freeway).
An alternative to surface or above ground freeway construction has been the construction of underground urban freeways using tunnelling technologies. This has been extremely successful in the Australian cities of Sydney (which has five such freeways) and Melbourne (which has one such freeway). This has had the benefit of removing traffic from surface roads and has led to urban renewal due to a significant decrease in surface road traffic congestion, noise and pollution. Public transport has been improved in these areas through the provisioning of dedicated bus lanes where previously traffic congestion prevented such lane allocations from being made.
Other Australian cities face similar problems (lack of available land, cost of home acquisition, aesthetic problems, and community opposition). Brisbane, which also has to contend with physical boundaries (the river) and heavy population increases, has embraced underground tunnel freeways. There are currently three under active development, one of which (the North-South Bypass Tunnel) is currently under construction. All of the planned tunnels include provisions for public transport, whether underground or in reclaimed space on the surface.
Freeway opponents have found that freeway expansion is often self-defeating: expansion simply generates more traffic. That is, even if traffic congestion is initially shifted from local streets to a new or widened freeway, people will begin to run errands and commute to more remote locations. Over time, the freeway and its environs become congested again as both the average number and distance of trips increases. This idea is known as induced demand.
Urban planning experts such as Drusilla Van Hengel, Joseph DiMento, and Sherry Ryan, argue that although properly designed and maintained freeways may be convenient and safe, at least in comparison to uncontrolled roads, they may not expand recreation, employment and education opportunities equally for different ethnic groups, or for people located in certain neighborhoods of a given city. Still, they may open new markets to some small businesses.
At present, freeway expansion has largely stalled in the United States, due to a multitude of factors that converged in the 1970s: higher due process requirements prior to taking of private property, increasing land values, increasing costs for construction materials, local opposition to new freeways in urban cores, the passage of the National Environmental Policy Act (which imposed the requirement that each new federally-funded project must have an environmental impact statement or report), and falling gas tax revenues as a result of the nature of the flat-cent tax (it is not automatically adjusted for inflation), the tax revolt movement, and growing popular support for high-speed mass transit in lieu of new freeways.
Meanwhile, in Great Britain, the related concept of the motorway was first proposed by Sidney Webb in a 1910 book, The King's Highway, but was not formally embraced by the government until the passage of the Special Roads Act 1949. In 1926, the English intellectual Hilaire Belloc recognized the necessity of grade-separated roads for "rapid and heavy traffic", but thought they would be the exception rather than the rule:
While Connecticut's Merritt Parkway was the first fully controlled-access highway in America when it opened on June 29, 1938, it does not qualify as the country's first freeway, since low bridge heights, tight curve radii, and short interchange ramps fell well below freeway standards. The first long-distance rural freeway in the United States is generally considered to be the Pennsylvania Turnpike, which opened on October 1, 1940. The Turnpike was so advanced for its time that tourists even had picnics in the median (that is, after it was already open to traffic) and local entrepreneurs did a brisk business in souvenirs. It was designed so that straightaways could handle maximum speeds of 102 miles per hour, and curves could be taken as fast as 90.
Shortly thereafter, on December 30, 1940, California opened its first freeway, the Arroyo Seco Parkway (now called the Pasadena Freeway) which connected Pasadena with Los Angeles. And in 1942, Detroit, Michigan opened the world's first urban depressed freeway, the Davison Freeway. Portions of the first freeway in Texas and the Southern United States, the Gulf Freeway in Houston, opened in 1948. Meanwhile, traffic in Los Angeles continued to deteriorate and local officials began planning the huge freeway network for which the city is now famous.
Today, many freeways in the United States belong to the extensive Interstate highway system (most of which was completed between 1960 and 1990). Starting in the 1970s freeways began to consider environmental factors, particularly noise and air quality in their location and design. Nearly all Interstate highways are freeways. The earlier United States highway system and the highway systems of U.S. states also have many sections that are built to controlled-access standards (though these systems are mostly composed of uncontrolled roads). Only a handful of sections of the Interstate system are not freeways, such as I-81 as it crosses the American span of the 2-lane Thousand Islands Bridge and a segment of Interstate 93 through Franconia Notch, New Hampshire that is a 2-lane road with partial access control.
Besides the U.S., some provinces of Canada have adopted the terms freeway and superhighway to describe comparable roads (instead of or alongside the term expressway) and they continue to extend their freeway networks. In Australia, some states such as Victoria use the term freeway (M1 Princes Freeway), and others such as Queensland and New South Wales use both terms, usually to distinguish between toll roads such as Brisbane's Gateway Motorway and toll-free roads such as Sydney's Warringah Freeway. However, many of Victoria's rural freeways have at-grade intersections and therefore would not be considered freeways nor motorways in other states.
Australia has been innovative in using the newest tunneling technologies to bring freeways into its high-density central business districts (Sydney and Melbourne). In Australia, the city of Adelaide pioneered the concept of a dedicated reversible freeway. The M2 expressway runs toward the city in the morning and out of the city in the evening. Its ramps are designed so that they can double as on- or off-ramps, depending upon the time of day. Gates and electronic signage prevent motorists from driving in the wrong direction. Brisbane currently has three major freeway tunnels under development; all are planned to incorporate traffic, congestion, incident and accident management technology.
Major progress has been made in making existing U.S. freeways and expressways more efficient. Innovations include the addition of high-occupancy vehicle lanes (HOV lanes) to discourage driving solo, and building new roads with train tracks down the median (or overhead). California's Caltrans has been very innovative in squeezing HOVs into limited right-of-way (by elevating them), and in building special HOV-only ramps so that HOVs can switch freeways or exit the freeway without having to merge across regular traffic. Many states have added truck-only ramps or lanes on heavily congested routes, so that cars need not weave around slow-moving big rigs.
Intelligent transportation systems are also increasingly used, with cameras to monitor and direct traffic, so that police, fire, ambulance, tow, or other assistance vehicles can be dispatched as soon as there is a problem, and to warn drivers via variable message signs, radio, television, and the Web to avoid problem areas. Research has been underway for many years on how to partly automate cars by making smart roads with such things as buried magnets to guide sensor-equipped vehicles, with on-board GPS to determine location, direction, and destination. While these systems may eventually be used on surface streets as well, they are most practical in a freeway setting.
Additionally, the original Highway Act of 1956 prohibited states from collecting tolls on Interstate-funded freeways. As more miles of freeways were completed, the cost of maintaining the infrastructure increased dramatically. A major issue that has slowed new freeway construction in America has been the application of highway funds to maintaining and repairing existing infrastructure. Most of the freeways in America are near or have exceeded their designed life span, which necessitates replacing of bridges and overpasses and reconstruction of the driving surfaces on many freeways nationwide.
To address the issue of lack of funding for new freeways and maintenance of existing roads, legislation enacted in 1998 gives states greater flexibility in funding major highway projects. Specifically the legislation, known as TEA-21 in official documents, authorizes states to add tolls to Interstate-funded freeways. Additionally, it gave states the latitude to enter into public-private partnership P3 arrangements to facilitate expansion and maintenance of the freeway network. Texas, Florida, Virginia, and California quickly took advantage of the TEA-21 legislation and began on massive projects to expand their respective states' freeway networks, complementing existing Interstate freeways with privately funded and operated tollways. In 2004, Illinois sealed a $1.8 billion deal with Macquarie Infrastructure Group and Cintras to operate the Chicago Skyway for 99 years. In a similar P3 arrangement in Indiana, the Cintras-Macquarie joint venture assumed responsibility for the Indiana East-West Toll Road for 75 years on June 30, 2006 in a very controversial $3.8 billion deal, which for political purposes was dubbed Major Moves. As of late 2006, Pennsylvania is actively pursuing the P3 toll road concept, but still has to clear challenges in the state legislature before such an arrangement can be implemented on the Pennsylvania Turnpike. Also in late 2006 Delaware has plans to enter into an agreement with a private firm to design, build, and operate a planned 17-mile (27 km) bypass of U.S. Route 301 between Delaware Route 1 and the Maryland state line. Meanwhile in New York and Massachusetts, the respective state public authorities that operate the New York State Thruway and Massachusetts Turnpike have generated enough revenue to assume maintenance of other freeways beyond the roads on which tolls are collected. The Massachusetts Turnpike Authority provided more than 50 percent of the funding to complete the Big Dig project in Boston, and later assumed responsibility for operating the Central Artery, the Sumner Tunnel, and the Callahan Tunnel following the project's completion in 2005.
As federal funding dries up for expanding and maintaining America's freeway network, states are looking to innovative solutions using a combination of state and federal funding, toll collection through public authorities, and private sector investment.