Here’s a chart courtesy of City Pages showing the bus on-time percentage during the big winter storm a while back. Transit ridership goes up in the wintertime as driving becomes more difficult. It’s good to remember that when contemplating how well to shovel your sidewalk.
Also, one of the big advantages of trains over rail is that they work much better in the ice and snow. I’ve seen lots of buses get stuck in the snow but I’ve never seen a train do so.