DETROIT — In the past 15 months, no one has been more responsible for safety on the nation’s roads than Ann Carlson. For much of that time she has served as acting administrator of the National Highway Traffic Safety Administration, where she started as chief counsel in 2021.But Carlson’s time running the agency and as its chief lawyer will come to an end on Wednesday. She’s returning to Los Angeles to resume teaching at the UCLA School of Law.During her tenure, the agency known by the acronym NHTSA …