After the war, Voorhees continued his education, graduating from RPI in 1947 and then earning his master's degree in city planning from the Massachusetts Institute of Technology in 1949.
In 1961, he began his own engineering firm (Alan M. Voorhees & Associates) which eventually grew to have branches in ten U.S. cities.
He was involved in the design of many subway systems including those in São Paulo, Hong Kong, Caracas, and Washington, D.C. Voorhees is credited with the concept for the Canberra 'Y Plan', linking Australia's capital city with new townships of roads and public transport.
Voorhees sold his firm in 1967 and became the dean of the College of Architecture, Art and Urban Science at the University of Illinois at Chicago Circle in 1971.
Voorhees and his family helped start the successful and family-oriented Westmoreland Berry Farm, located in the Northern Neck of Virginia.
The system he supported involved scanning thousands of land records in the county clerk's office and connecting these with data from the county planning office (topo maps, sewer and water overlays, satellite views, etc.)
He donated over 700 acres (2.8 km2) of land along the Rappahannock river in Virginia to become the Voorhees nature preserve.
[3] His interest in government automation was designed to make it easier to identify environmentally sensitive areas and ensure that development took them into account.