Under Mackie's aggressive leadership as state highway commissioner from 1957 to 1965, Michigan moved to the nation's front rank in highway construction. Throughout most of his administration, the state led the number one position in construction of its interstate freeway system and was the first to build a cross-state interstate freeway (I-94). Mackie was the first commissioner to propose and carry out a five-year construction program, all based on priorities determined solely from engineering criteria. His strong advocacy of bond financing helped Michigan improve a first-rate highway system while keeping it toll free. He was president of the American Association of State highway Officials in 1963.