That may be stating the obvious, but it represents a major problem that can't be legislated for, although in the case of professionals, limits can and should be put on the amount of time they spend behind the controls over a given period.
A recent episode of 'Mythbusters' found that driving tired can result in even worse impairment than driving tipsy. The power nap principle, i.e. a short sleep of about 20 minutes, has been well established to be beneficial in workplace situations and this South Australian government webpage says that if you rest every two hours for at least 15 minutes driver
fatigue can be avoided and you will have a safer, more enjoyable trip.