US millennials are slowing their roll when it comes to car travel. A new study published in the peer-reviewed journal Transportation Research Part A: Policy and Practice found a wide generational divide in the daily driving habits of adult Americans. Millennials (those born between 1981 and 1996) are driving 8% less than Gen X (1965 to 1980), and 9% less than younger baby boomers (1956 and 1964).