First, it's unlikely, as most trips happen in small windows of time, and in the same general directions in a city, leading to very little chance to reuse: Peak cars on the road at 8 am on a Tuesday is not really going to drop, and then very few trips will be happening at 2am. It's the same thing that happens in many US cities for commuter trains: A large fleet spends the night on depots far from the center, and then makes a single trip downtown, where they stay put all day, just to make a lone trip out later in the day: The demand is just too low in the other direction to not have most trains idle most of the day.
But let's ignore that fact, and instead look at a different definition of number of cars on the road: Instead of how many cars actually exist, count how many cars are on the road at any given time. It's not just that there might be more cars in the end, but even with fewer cars, each car will be doing more miles, because you don't need a driver. Children visiting each other while being less of a nuisance for parents mean more trips. Old people that are uncomfortable driving. People going further away in geneeral, because being driven would be less stressful when the technology is doing well. More visits to the bar, now that you don't have to call an uber, or risk a DUI on the way. And let's not forget letting the car go back home to park, instead of paying for expensive downtown parking: Same number of miles with a passenger, but bonus congestion for everyone else.
When driving is cheaper, the number of miles driven goes up, and therefore the number of cars that you actually find on the road goes up, even with fewer cars.
But let's ignore that fact, and instead look at a different definition of number of cars on the road: Instead of how many cars actually exist, count how many cars are on the road at any given time. It's not just that there might be more cars in the end, but even with fewer cars, each car will be doing more miles, because you don't need a driver. Children visiting each other while being less of a nuisance for parents mean more trips. Old people that are uncomfortable driving. People going further away in geneeral, because being driven would be less stressful when the technology is doing well. More visits to the bar, now that you don't have to call an uber, or risk a DUI on the way. And let's not forget letting the car go back home to park, instead of paying for expensive downtown parking: Same number of miles with a passenger, but bonus congestion for everyone else.
When driving is cheaper, the number of miles driven goes up, and therefore the number of cars that you actually find on the road goes up, even with fewer cars.
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