Jennifer Yates is directing traffic today — a routine happening as part of her job as head registrar at the Petersen Automotive Museum. This late January afternoon, however, traffic is especially gnarly — and not because it’s a Friday. Several valuable vehicles are arriving at — or leaving — the museum today, a coincidental calendar smashup that has Yates ping-ponging between projects. First, there were the Hetfield Collection cars, donated to the museum in 2019 by Metallica’s James Hetfield, Yates says while striding up and down South Orange Grove Avenue, a side street onto which the museum’s car elevator deposits vehicles from the mechanics shop below. Those 10 customized cars…