I'm not sure that's a fair comparison. The most expensive part of self driving cars is building the roads and highways. Would make more sense to compare Waymo to the operating expenses of PT, hiring the drivers and maintaining the trains.
You are suggesting that we should attribute a fraction of the costs of our road building and/or maintenance under autonomous vehicle development? If so, what fraction are you proposing?
Building roads for buses are _few orders of magnitude more_ expensive than roads for cars only.
Unfortunately we still have trucking, but it's starting to feel we should build separate roads for them and for special cases only allow multi-axle delivery trucks on normal roads.