While I think battery technology has progressed a lot in recent years, for long-haul trucking and even long-distance bus transportation, I think trackless trolleys along interstates and major highways. I know a lot of people discount the possibility — after all it is expensive to run thousands of miles of electrified wires along with all the substations required to supply the wires, but it could provide a an economical source of power on go, beyond what even a large battery bank could provide.