swordshapedleaves asked:

What's the difference between light rail and heavy rail for metro commuter trains? Obviously the weight of the rails but what are the different pros and cons of each?

My city has been expanding a network of light rail lines the last ten years and it's been a big improvement over no rail, but I just saw you mention heavy rail metro in another post so now I'm curious.

Light rail is a very vague term, it basically is a cheaper slower kind of rail that often runs at grade on streets, while heavy rail is faster, grade separated and has higher capacity. But these rules are not a garenteed way to tell which is which. Seattle and Minneapolis is Light rail, NYC and Chicago are Heavy.