Public transport advertising

Following my decision as to what I want to do for this brief I have been looking at different ways of advertising on public transport.

I was thinking of advertising in tube stations in London and actually on to the trains themselves as, when people are sitting about waiting, they generally look at what is around them, even if sometimes it is subconsciously, it goes in. I remember a certain advert from years ago just from it being repeated constantly throughout the underground system.
Advertising on buses is a tricky print procedure, but it is effective, take these two successful campaigns, simple but genius. These would definitely stick in people's minds, effective.