История развития эстакадных дорог и магистралей в США.

An elevated highway is a controlled access highway that is raised above grade for its entire length. Elevation is usually constructed as viaducts, typically a long pier bridge. Technically, the entire highway is a single bridge.

Concurrently, the increase of automobile and truck traffic early in the 20th century exacerbated many of the safety and free flow issues the railways already presented and in fact, created additional hazards with railways. The increase in traffic also meant that for the first time, there was a need to develop new and improved roads between cities. By the 1920s, truck traffic in warehouse and dock areas was high enough that there was frequent congestion and frequent accidents. In 1924, New York City began looking for ways to relieve the problems of the combination of trucks, cars, trains, and pedestrians on 11th Avenue, which had been known as Death Avenue even before the advent of the car and truck. After an interruption for World War II, several extensions were built from 1947 to 1951, under the leadership of urban planner Robert Moses, primarily connecting it to his other projects, such as the Henry Hudson Parkway and Brooklyn Battery Tunnel. The Miller Highway influenced many other subsequent projects, such as Boston's Central Artery and the Pulaski Skyway, and Moses' own Gowanus Parkway. At the start the 20th century, New York and New Jersey state officials realized that car traffic on ferries was increasing beyond the ability of the then current ferry system. Planning for the Holland Tunnel started in 1919, and it was constructed from 1922 to 1927. As construction started, New Jersey began planning traffic flows between the tunnel and nearby cities. The legislature passed a bill to extend existing highway Route 1 east through Newark and Jersey City. Due to local opposition to having new highways disrupt local traffic patterns, the engineers elected to use a viaduct, which became the Pulaski Skyway for the eastern portions of the new route (until close to the entrance of the tunnel). It opened in 1933. Like the Miller Highway, it included left lane exits and entrances, narrow lanes, and local surface lanes underneath the highway. The Miller Highway, through immature design and resulting problems, became a case study for highway engineering improvements. Engineering of paving, exit orientation, turn radius, drainage, curb height, ramp length, speed optimization, shoulders, maintenance procedures, noise abatement, and minimizing the "highway wall" effect that could divide communities, were all improved in the 1940s through 1970s, partially by examining the deficiencies of this early elevated highway.

In the mid 1930s, US Federal Highway legislation allocated budget for surveying and planning of roads, including "superhighways", across the nation, and ordered the chief of the Bureau of Public Roads to report findings and recommendations. The report, submitted in 1939, included a master plan, which recommended that urban highways be "depressed or elevated". In 1944, President Franklin D. Roosevelt submitted a follow on report, Interregional Highways, which contained illustrations of the depressed and elevated designs. The elevated illustration, reminiscent of the Miller Highway and some of its descendants, featured partial left lane ramps, a highway running across the width a populated boulevard, almost building to building, a local traffic lanes underneath the highway. The report also includes a picture of the then recently constructed Gowanus Parkway, and noted how it was thought to have been an appropriate placement that had a minimal effect on the community. (This was later disputed, and the Gowanus is also a case study for how elevated highways divide neighborhoods and contribute to urban blight.) The phrase Interregional Highways gave way to Interstate Highways in a Congressional bill in 1944, and included $125 million for urban highways. The lead agency, the Federal Public Roads Administration (PRA) worked with state engineer associations to develop planning and design criteria. The PRA's leaders, especially Thomas H. MacDonald and Herbert S. Fairbank, were especially concerned about urban highways.

Elevated expressways are now common around the world, particularly in the central urban areas where traffic volumes and urban densities are high such as cities in the Americas, East and Southeast Asia. Entire networks of elevated expressways exist in the central areas of cities such as Metro Manila, Guangzhou, Bangkok, Osaka, Shanghai, Tokyo, and Wuhan.