In my state, the minimum yellow light length is 4 seconds, but it's obviously not uniformly applied. You can get a device to time the yellow lights from the state if you get a ticket, and then use that info to dispute it. Not much help if there is an accident.

It's a big enough problem that there's a group trying to do something about it.

http://shortyellowlights.com/standards/

EDIT: according to the link, the yellow light for a 55 mph road should last 6 seconds.