Noun
motor voter (plural motor voters)
(US, chiefly attributive) A person who registers as a voter while applying for a driver's licence.
Clinton gave his assurance to Lippert that he would support what became known as the “Motor Voter Bill” and, as president, name-checked the organization at the signing ceremony. Source: Internet
Wagner compared it to the 1993 federal Motor Voter Act, which required states to offer registration to anyone getting or renewing a driver’s license. Source: Internet