If the goal is prepping the layout for autonomous vehicles, designing for buses forces you into some compromises you wouldn't ordinarily make. Your roads have to be wider, for example. Your overhead clearance is higher. And you have to select routes that maximize foot traffic. Vanpool? You could build for that now and assume it's future-proof. After all, any AV fleet isn't going to seat four passengers. It's going to seat ten. There are lanes in Vancouver BC that are limited to 8 passengers or more. I would say expand the bus network such that the definition of "bus" includes lower-capacity vehicles but doesn't include carpool. It'd be an easy pilot project to roll out.
You mention width, which makes me realize something: there's no reason for a bus-lane AV service to stop everywhere. This means that cars should be able to pass at stops, which is possible when the road is as wide as bus lanes are. Bus lanes here are around 6.5-7.5m, and car lanes can be as slim as 2.2m, so bidirectional bus lanes now could be three-lane AV lanes in the future. Overhead clearance is a good point, although I think clearances are pretty well-standardized at 4m.