It's foolproof.

Here is the proper formula for being able to sleep on the bus:

1. Eat a deliciously enormous English dinner (roast beef, veg, yorkshire pud, trifle...the works) at 3 pm.
2. Go for a really really long walk (at least an hour and a half)
3. Take a Gravol.
4. Read a book while waiting for the bus to come. Preferably something not too hard to read -- a favourite children's novel works well.
5. Board the bus and listen to soothing music while the sun slowly sets.

Just remember to position yourself so that you don't drool on anyone.

Sweet dreams!