Elevated highway

The existing street grid also made it difficult to lay some railroad lines, as the trains required a wide turn radius.

[2] The mayor, the Manhattan borough president, the police commissioner, the Port Authority, the New York Central Railroad (owner of the West Side Line whose tracks were on 11th Avenue), and others worked on various plans to take the railroad and passenger cars off the street, eliminating the major conflicts that led to injury, death, property damage, traffic jams, and delays in service.

[3][4] 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.

[3][5] The Miller Highway influenced many other subsequent projects, such as Boston's Central Artery and the Pulaski Skyway, and Moses' own Gowanus Parkway.

In 1944, President Franklin D. Roosevelt submitted a follow-on report, Interregional Highways, which contained illustrations of the depressed and elevated designs.

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.

The lead agency, the Federal Public Roads Administration (PRA) worked with state engineer associations to develop planning and design criteria.

Entire networks of elevated expressways exist in the central areas of cities such as Metro Manila Skyway, Guangzhou, Bangkok, Osaka, Shanghai, Tokyo, and Wuhan.