BBC News - Lorry drivers who drink coffee 'cut their crash risk' Yet the medical profession tell us that if you have two caffeinated drinks, you'll have a job getting to sleep. Besides, isn't napping while driving dangerous? Personally, I don't think it's the caffeine that benefits alertness, it's the background activity. You feel your eyelids dropping so you reach for your cup - it's the stimulus of movement that breaks the monotony. You'd get the same effect by smoking a cigarette, sucking sweeties or wolfing down sandwiches. The most effective stimulus provided by the Army that I've experienced was reaching into my haverbag in the wee hours during a night time convoy move to find a hard boiled egg complete with shell. Carefully peeling the shell off in total darkness dispelled any thought of sleep.