[jyl]

A good book on tape/CD is the most effective keep-awake for me. Loud music, open windows, coffee are less effective.

Usually when I'm struggling to stay awake on the road, I'm not actually exhausted. It's just that my mind reacts to boredom by falling asleep.
And I have a really low threshold of boredom. One hour behind the wheel can have me yawning and sleepy.

I guess some of us live in a near constant low level of sleep deprivation too, what with work hours.

When I was younger, I used to drive between LA and SF often, like monthly. It was an 8 hour drive in my old VW. I didn't have much trouble with sleepiness, maybe because of youthful energy or chemical enhancements. But I'd often slip into autopilot mode and then "come to" with no memory of the past hour.

You want a good read along these lines, I recommend The Spirit of St Louis, Lindbergh's classic tale of his solo NY-Paris flight. He took off after having been awake for some 20 hours, and fought against sleep for much of his flight, as he skimmed 50 feet above the North Atlantic wavetops. He said that the Spirit was a twitchy plane which helped him stay awake.