Are trolleys more efficient than buses, pound for pound? Especially after you factor in the capital expenditure needed to build out the trolley lines? I find it hard to believe that a niche technology (trolleys) would be more efficient overall (impact * quantity) than buses, which are everywhere.
Buses are probably an 'easier' problem, but it's much easier to pitch selling self-driving cars to individual consumers rather than to government procurement budgets. Also, I suspect the bus problem space introduces additional issues such as <what to do when some asshole is parked in the bus bay>.
You seem to be thinking of trams, while nimos is talking about trolleybuses, which are buses that draw their power from overhead wires [0]. Specifically they're suggesting that a hybrid option with batteries would reduce the need for wires everywhere (just run on battery power), but would still allow the buses to charge while connected to the overhead wire.
Buses are probably an 'easier' problem, but it's much easier to pitch selling self-driving cars to individual consumers rather than to government procurement budgets. Also, I suspect the bus problem space introduces additional issues such as <what to do when some asshole is parked in the bus bay>.