She doesn’t need an alarm clock, Carolyn Cherry says. Her brain is programmed, by years of routine, to sound an internal alarm just before 3 a.m.

One hour after rising, she leaves her house in Hemet and drives in darkness to the South Perris Metrolink station, the first leg of her daily journey to work. The drive takes 22 or 23 minutes, a bit longer if she picks up a friend or stops to get a cup of tea for the long train ride ahead. The parking lot is all hers when Cherry arrives, and she pulls into the same spot every time.