Hi Isomers007,
The mood of the first picture striked me immediately. The second one is good too!
For a while I wanted to take a series of pictures of billboards through the windows with passengers in front of them. Which kinds of necessitates sitting at the "better seats". Sometimes I miss certain shots, and to go back and try to recapture the shot means a certain amount of spontaneous excitement discvoering and capturing the shot is gone.
On privacy: Theoretically I think MRT trains are enclosed spaces, and semi-public/private. If you are brave forget the above hogwash and just shoot the pictures. The more you do it the more confident you get.
There was a MRT juxtaposition shot that won a local competition before

A boy with cheeky face peering into the lens from billboard with bored passengers sitting around. (and ok, in black and white ;p )