Car companies closed a lot of North American factories in the past ten years as the auto industry restructured.
That has made Jim Tetreault's job even more of an art and a science.
Tetreault is Ford's head of North American manufacturing. He's responsible for maximizing the number of vehicles that any of the Detroit automaker's remaining plants can produce, while minimizing the downtime at each facility.
"Ten years ago, production plants ran two eight-hour shifts, five days a week," says Tetreault. "That has shifted dramatically, not just at Ford but throughout the industry."
Tetrault says some Ford facilities are running on four shifts, producing vehicles 140 hours a week.
This summer, Ford plans to shut down 20 of its facilities for only one week. The traditional shutdown period is two weeks.
But he says some facilities will have to shut down no matter what the demand situation is - for required maintenance of paint shops, for example.
Chrysler is eliminating the summer shutdown altogether at three factories, and four others will be shut down for only a week.
General Motors hasn't made public its plans. But an erroneous AP broadcast report saying GM was canceling all its summer shutdowns caused widespread consternation at the Grand River Assembly plant in Lansing, according to Krystal Hoag, who works the second shift there.
She says as far as she knows, "we're still scheduled for a two-week shutdown - but in August instead of (the usual) July."