There are two questions that may have different answers:
1. Will it mean fewer total cars? Probably. If I have to drive to work and then back home, and you do to, and we each own cars to do it, that's at least two cars. If I can take a Waymo to work, and then it can take you to work, that's only one car.
2. Will it mean fewer cars on the road? (Or, perhaps, let's say fewer car-miles driven.) Plausibly not. If I drive from home (A) to work (B), and you drive from home (C) to work (D), then if we own cars, we drive A-B and C-D. If we use Waymo, it may drive A-B-C-D, which is longer by the B-C leg. That takes up space on the road.
So we may have fewer total cars, but more car-miles driven, and therefore more traffic and congestion.
1. Will it mean fewer total cars? Probably. If I have to drive to work and then back home, and you do to, and we each own cars to do it, that's at least two cars. If I can take a Waymo to work, and then it can take you to work, that's only one car.
2. Will it mean fewer cars on the road? (Or, perhaps, let's say fewer car-miles driven.) Plausibly not. If I drive from home (A) to work (B), and you drive from home (C) to work (D), then if we own cars, we drive A-B and C-D. If we use Waymo, it may drive A-B-C-D, which is longer by the B-C leg. That takes up space on the road.
So we may have fewer total cars, but more car-miles driven, and therefore more traffic and congestion.