I don't think it is so simple. Eg: people now taking extra trips because it is easy and cheap to do so. Eg: "I'll just Uber the 6 blocks to my next shopping spot" instead of walking. This happens in my friend group all the time. Plus people traveling to the city at all BECAUSE Uber makes intracity travel easy. Eg: I live in the East Bay and hate driving within the city, but am happy to be escorted around it on a whim but would have otherwise stayed more local.
Funny you say that because most of my Uber/Lyfts consist of me going to and from public transit for my intended destination.
Although it is more complicated than that, as I often take a shared ride home because Bart shuts down too early on weekends to be useful on the way back.
Additionally the math gets complicated when I have multiple people with me, as often times it's cheaper to uber/lyft somewhere to our destination than it is for all of us to individually pay for a Bart ticket.
This is called multimodal transport. I'm unsure how big the effect is for Uber/Lyft where booking the ride would seem slightly more involved than, say, using a bike. But it's an area of great interest especially for public transit planners.
I'm only comparing what happens in the world we have, where Uber & Lyft exist, vs. what would happen if they didn't, or would've happened back when they didn't. Obviously some of this is guesswork kind of like "Gee what would've happened if I'd married my high school crush" or whatnot. But in general if you would've walked or biked to transit before, and now you take Uber & Lyft, that makes congestion worse. If you would have driven to transit, using Uber/Lyft has no effect. If you would have driven the whole way, it's a partial improvement (by riding transit for that one segment).
Actually, you take that number, PLUS the number of empty Uber cars, PLUS the number of empty taxis that would not have been empty if there wasn't Uber...
That just isn't true. They often do drive around and look for fares or go back to a place where they can collect a fare from where one did not exist. Example you pick up Passenger A in dense urban center drop them off in suburb no fares exist there. You need to drive back to the urban center to pick up another Passenger. You have worsened traffic and created extra carbon pollution.
So, we consider people being able to do something in a way they would much rather do it as a negative? If you have the choice between walking and an Uber, and you really want to walk, then just walk. If you have the choice between walking and walking, but you really don't want to walk, then you're worse off.
Clearly a trip that is taken has utility to the person taking the trip, so the "not at all" outcome is a bad one.
People will use the best option they have out of the ones available to them. Transit is usually faster than Uber for trips to downtown or the Mission, but try getting to Miraloma with it.
Every trip has a cost. It's a transaction. If it costs me $1,000,000 to get to the park (and it's fairly likely I won't make $1M at said park), I will maximize utility by not taking the trip.
In addition, every trip by you, has various costs to everyone else, namely the traffic congestion we're talking about here, plus many other things we're not talking about like pollution, publicly-subsidized police/EMT/fire for cleaning up your car wrecks, etc. Transport modes that allow you to take up less space on the roads per person, or that use separate parallel networks, or that don't pollute or involve wrecks, cost everyone less on these particular axes.
And, following this, these different effects probably have different values for society, i. e.:
- Replacing public transit = unmitigated bad
- Replacing walking, bike = even worse, bikes are unbeatable for health, space efficiency, energy use, noise, and really any other category
- Replacing using own car = close to neutral, maybe slightly positive, especially when it allows people on the margin forgo car ownership entirely
- Non-consumption = likely positive, taking a trip you otherwise wouldn't take is a sign of increased freedom/participation in society and would tend to outweigh environmental concerns in my subjective judgement
There's also a larger impact for cars that block traffic by stopping in the lane in front of a pickup or drop address where there isn't room to pull over.
And there's an impact from out-of-town weekend drivers that don't know where they're going and take a dumb route because of that unfamiliarity.