Probably more than any other legislator, O'Brien was responsible for passage of Act 51 of 1951, the bill that became Michigan's basic highway law and a model of highway administration for the entire country. He led a group of legislators who insisted that highway authorities at all governmental levels agree upon a unified position for administration and financing of roads, streets and highways. When the measure was vetoed, he risked his political career and became virtually a party outcast by providing the vote needed to override the veto. Through 32 years in the Legislature between 1940 and 1974, on the house Roads and Bridges Committee and later the Senate highways and Transportation Committee, he was an unfailing advocate of good-roads programs.