Whenever I'm short on sleep hours, I try to sneak in some sleep time during my travel to and from work. It doesn't always work for me since the vehicle ride isn't exactly comfortable, but when you're really sleep, you won't be able to help falling asleep despite your not conducive for sleeping surroundings.
Of course, whenever you sleep during traveling in a public vehicle, it's important to make sure that your belongings are well accounted for. Always put them in front of you, where you'll be sure to wake up if ever someone tries to take it. Remember, it's important to get enough sleep, but taking care of your valuables is important too!