Yea they could put down visual markers on the road to make it easier for CV or ML models to be trained against, or maybe even physical tracks to mechanically guide these cars so that minimal software is needed. Multiple cars can be linked together for efficiency.

If you'd build a genuinely smart city completely from scratch, the most elegant way would be to completely remove the need for own cars. But that's obviously not going to happen when its a project designed and financed by an automaker.

A car that can drive itself in a specifically prepared environment would hardly qualify as "fully self driving". You could achieve that with all the AI prowess of a mechanical connection between the steering linkage and some guide rails. And you'd still fail to get even the tiniest development budget for a car that won't sell anywhere else.