As the dean of Michigan's highway legal experts, Cushman was widely recognized as a leading authority in drafting and advancing legislation affecting transportation at the county, state and local levels. He served 34 years with the Wayne County Road Commission (1945-1979), including 18 years as general counsel, and 14 years as legal consultant to the County Road Association of Michigan (1979-1993). He laid legal groundwork for the basic freeway network in Wayne County and for bonding by counties and cities to pay for their portion of the state freeway system. Cushman also played a critical role in development of the Wayne County Detroit Metropolitan Airport, involving airlines in a bonding concept since copied by major airports throughout the country.