> It can only reduce congestion if multiple passengers on different trips are in the car at the same time.
Not _only_: in the general case, there's nothing stopping taxi services from providing a last-mile (or rather last-n-miles) connection to transit compared to a car trip for the entire time. Depending on the way this works out, congestion can be reduced with private taxi rides. In fact, Beverly Hills city council passed a resolution to investigate driverless shuttles for exactly this purpose and precisely to reduce congestion.
Not _only_: in the general case, there's nothing stopping taxi services from providing a last-mile (or rather last-n-miles) connection to transit compared to a car trip for the entire time. Depending on the way this works out, congestion can be reduced with private taxi rides. In fact, Beverly Hills city council passed a resolution to investigate driverless shuttles for exactly this purpose and precisely to reduce congestion.