The only 'bump & reverse' Dept. 56 ever released under their own name ran on HO track. The trolley itself was sort of between HO and On30 scale. Other 'bump & reverse' trolleys were O27 (1/50) size, made "for use with Dept. 56" and ran on 3-rail Lionel style track. Bachmann also did an On30 trolley for Dept. 56 that operates on HO track and used their electronic reversing unit, rather than 'bump & reverse'.