Why Pennsylvania police stop tractor trailers during some winter storms

(WHTM) -- While abc27 News' live crews were out during this weekend's storm, they saw dozens of snowplows, stuck vehicles and Pennsylvania State Police pulling over tractor trailers. Crews didn't confirm exactly why troopers stopped the vehicles, but Fritzi Schreffler, a PennDOT spokesperson, stressed commercial vehicles are not allowed on interstates when a Tier 4 [...]