Comment Humans are diurnal (Score 4, Insightful) 545
Humans are diurnal (dI-UR-nal).
It means we sleep when it's dark and wake when it's light. (compare nocturnal)
The primary purpose of DST is to keep our scheduled wake time (as determined by school, work, etc) close to sunrise.
Everything else (energy savings! more shopping hours!) is just confusion and wishful thinking.
The controlling factor isn't east-west, it's north-south.
The further north you go, the more sunrise time varies with the seasons, and the more an adjustment like DST helps.
Stuffing the whole country into two time zones is a non-fix for a non-problem.
See also
How congress broke Daylight Savings Time
http://world.std.com/~swmcd/steven/letters/dst.html