In 1925 he became traffic engineer of the City of Detroit and in 1927 for another two years he was the traffic engineer of Essex County, New Jersey working on traffic surveys and plans there.

The next two years were with the American Transit Association as research engineer on transportation and traffic research.  Mr. Simpson was perhaps the first Institute member to devote a great deal of time and study to transit problems.  In his work with the American Transit Association he became active in labor matters, arbitration and the like and became a spokesman for the transit industry before the National War Labor Board.

During World War II he served as a consultant without pay to the Office of Defense Transportation.  In mid-August 1945 after World War II was over, Mr. Simpson opened a consulting office in Philadelphia.  Activities of his firm related almost entirely to transit.  In 1947 he formed a partnership with John F. Curtin specializing in transit.

Mr. Simpson was a founder and one of the staunchest supporters of the Institute in its early days.  He was its first Secretary for a long period from 1930 to 1935, was Vice President from 1937 to 1939 before becoming President.

An avid writer and lecturer he won the Arthur M. Wellington prize from ASCE in 1935.  He retired from his consultant practice in the 1970s and moved to Florida where he died in September, 1974.