If it’s cold enough to freeze the ground, I’m not riding my bike. First, having the right tires is one thing, but black ice and surprise potholes will eat your snow tires. Second, it’s going to be too cold to be out in the cold air for the several hours you need to bike to school or work.
Busses require the same amount of roads as cars. So you’re going to need the same amount of salt for busses. You might need less for sidewalks, but that’s only because people cannot walk as far as they can drive.