Ya, the new first hill trolley is sort of like that already.
Seattle used to have a lot of dual electric diesel buses that would be diesel outside of the downtown bus tunnel and then catch onto overhead lines before entering the tunnel. However, this didn’t really work out very well (hooking up to overhead wires was error prone). They just use NG buses these days
Seattle used to have a lot of dual electric diesel buses that would be diesel outside of the downtown bus tunnel and then catch onto overhead lines before entering the tunnel. However, this didn’t really work out very well (hooking up to overhead wires was error prone). They just use NG buses these days