Here in the Great Grey Northwest, light rail transit is also more reliable in snow & ice than a bus. Seattle's Metro Transit uses mostly an articulated bus design, with the diesel engine BEHIND the articulation joint. This design, while quieter for most of the passengers, will usually shove the bus into a jack - knife in icy or snowy conditions. The passenger car - style cable chains Metro uses on drive tires usually come off within a mile or two of the bus barn; or they break at highway speeds. I recall last winter driving a slalom course around spun - out Metro busses on Hwy. 518, going up the hill from I - 405 to SeaTac Airport, and watching a Link Light Rail train grinding up the grade next to the highway that the busses couldn't climb.
Electric trolley busses, used in the hilly areas of Seattle's Capital & First Hills, cannot go around stalled traffic or use other less - icy streets due to the wire issue Matt mentioned. Much of the electric bus fleet is articulated as well, leading to the same issues I've pointed out above.