Until Antonio Villaraigosa, Los Angeles was a city dominated by cars, freeways and the worst traffic jams in the country. But L.A.’s most recent mayor began a shift away from that transportation monoculture by ramping up bus and rail service to a degree unseen in city history. He pulled this off thanks in no small part to Measure R, a half-cent sales tax that L.A. County voters approved in 2008, and which will generate a projected $40 billion for transit investment over 30 years. But Villaraigosa is out of office now, and it will fall to his successor, Eric Garcetti, to try to keep up the momentum. In his June inauguration address, the new mayor kept the focus on smaller transportation improvements — like filling potholes — and though he’s promised to follow through on five major transit projects already on the table, he hasn’t introduced any additional ideas for the future. Garcetti will have a spot on the Metro board of directors, but he and his allies will have to contend with commissioners representing parts of the county far from L.A. proper. Writer Nate Berg sets out to see if Garcetti will keep Los Angeles on track in one of the most dramatic turnarounds any American city has seen on its transportation front.