In three terms as governor (1921-1926), Groesbeck led the way in converting the state highway system to one of the most modern in the United States. When he took office, most state highways were gravel. When he left, Michigan boasted 3,398 miles of new highways, including 1,200 miles of concrete. He backed bonding for roads and user financing and supported adoption of the first gasoline tax, the main source of highway revenue. The ferry service at the Straits of Mackinac was established under his administration. A "Wider Woodward" Avenue, built at his urging from downtown Detroit, was the forerunner of today's freeways.