Art on the Metro! London, Stockholm... any where else?

Question

I'm going to write an essay the types of art commissioned for LU's Art on the Underground, comparing it to the works exhibited in other European metro systems. Can anyone tell me some other places, other than Stockholm, which have major art exhibitions on their underground/public transport networks?

Answer 1

The website below is a guide to all of the art on the NYC subway.  The second website is the "official" guide.  The third is a rating system of the art in the subways around the world.

There is also major art in Naples, Brussels and Montreal's subways.