If a car that would otherwise be parked for 8 hours in the city can instead drive 30 minutes back to the suburbs, park for 7 hours, then drive back in, we can trade 1 car-hour of freeway and 7 car-hours of suburban parking to regain 8 car-hours of city parking. And maybe we think that suburban parking is 'free' because it would have otherwise been sitting empty.

Obviously within the constraints of that model it's still debatable whether that's a good deal, between the emissions and the doubling of near-rush-hour freeway traffic.

And beyond that simple model, how cars performing pick-ups will impact congestion and whether people are willing to summon their cars 30 minutes in advance is also debatable.