Self-driving cars will likely kill PRT ambitions by being a better band-aid for long enough to not have to think about the problem for a while, like how successive attempts at solar power were buried for more than 100 years by more efficient coal extraction, then oil, then nuclear, then oil, again.
Self-driving cars aren't a band-aid. In the long term, where every vehicle on the road is self-driving, then they're the best solution possible (for any travel distance that doesn't warrant something like Hyperloop / planes / trains). I say this because self-driving cars can go everywhere (that cars can go). Pods have a fixed track, they can only go where there's track to go. The only way for Pods to be better than self-driving cars is if we rip up all the roads and replace the entire road network with a pod track network, but that obviously will never happen (and even then it's not necessarily better, because a pod track network could only be used for pods, but roads can be used by a lot more than just cars).
Self-driving cars would still be less workable than rail when there's a certain level of density. I can't see New Yorkers all loading up in self driving cars; they just don't scale as well as trains do. Even assuming quadruple capacity from the roads, you would still need a large number of fairly beefy bridges and tunnels to get everyone coming from outside of Manhattan into Manhattan.
Oh sure, there's still a need for high-capacity mass transit options. But mass transit cannot go everywhere (or even most places). My argument here is strictly about personal transport (which is what Pods are).
In what way do they not scale as well as trains do? I think self driving cars will probably introduce a huge pile of problems, but that particular claim seems odd to me.
It comes down to space. Cars occupy way more space per passenger than trains do. A fully loaded subway train can easily carry almost thousand people. The 7000 series in the DC Metro carries ~175 people per car maximum, and the trains are 8 cars long, for 1400 people per train. Normally, 26 trains per hour are scheduled during rush hour, allowing up to 36,000 people per hour if all trains were 8 cars long (they currently aren't due to power constraints). Other systems that have longer trains, better headways, and better seat configurations have way higher capacities. New York for instance could achieve much greater capacity given its longer trains and a modern signalling system.
By contrast, a road lane (which uses the same space) currently typically carries around 1000-2000 cars per hour. In ideal circumstances it can be almost 5000 cars per hour. Even assuming quadruple capacity from self driving cars (not realistic), 20,000 cars per hour in ideal circumstances would compete with trains at a far higher environmental cost.
But in more realistic scenarios with quadruple capacity, 4000-8000 cars per hour would fall way short of a train. Given that we have to account for pedestrians, cyclists, etc., I can easily see traffic lights continuing to exist, making self driving cars not achieve the miracles people expect.
This certainly would not solve traffic congestion issues. Other modes of traffic address traffic much better than more cars/same number of cars does. If a car can't make it across town in an hour at rush time, then "everywhere cars an go" isn't that much of a selling point since cars can't really go that far then in a good amount of time.
Once everything is self-driving, they can coordinate much better than humans and fill roads to their capacity (as well as routing intelligently since we'll be able to have completely accurate traffic predictions, although that demands a level of widespread coordination that won't necessarily come at the same time as 100% self-driving vehicles). You can also throw vans/busses into the mix if the roads still can't keep up, or automated carpooling services.
100% self-driving vehicles will be able to fill roads to capacity for 2 reasons:
1. It's all automated, so most of the common causes for traffic jams simply won't happen (most traffic jams happen spontaneously once the road reaches a high percentage of capacity, rather than for any concrete reason that demands a jam, and self-driving cars will be able to avoid the turbulence that causes the jams).
2. Because it's automated, cars can also drive faster while remaining safe, and drive closer together as well. By the time we're at 100% self-driving cars the driving software will be pretty well-tested, so the only significant risk* will be a mechanical failure in the car, and even if that happens, because everything's automated the surrounding cars will be able to adapt much better.
*I'm talking here about accidental risk. Any kind of intentional issues (hacking the car, throwing heavy stuff at the car from another vehicle, etc) are not particularly relevant here.
I guess you (and danmaz74) have a point here. In both my supposition and yours, we are assuming computers are smart enough to coordinate the vehicles well, only for cars, the infrastructure already exists. I guess my only reply here is that, yes, there is the cost of the infrastructure itself; however, let's say that this PRT thing takes off, the fact that their infrastructure is physically separate from the road, it would initially alleviate traffic issues much more than self-driving cars would. Having to deal with irrational, nondeterministic human drivers would probably make traffic alleviation not as apparent at first compared to a completely parallel infrastructure.
Still, this does ignore adoption rates. In a more real world, I think you'd argue that adoption of self-driving cars would be quicker and easier than adoption of PRT, that might hamper my model. So, perhaps the conclusion of the article is right after all.
What is the capacity of a road with 100% self-driving cars, and how does that compare to the capacity we are utilizing today? And how could traffic jams not happen? What happens when you exceed the capacity of a road? If you just wait in your autocar to get on the road, that seems similar to a traffic jam.
Traffic jams spontaneously occur before roads reach theoretical capacity. You should look up information yourself on that if you're curious (because offhand I'm not sure what to search for).
Right, so 40 years later we have 100% autonomous cars and use the entire road capacity of 20% more than we currently use. Also more people are driving so we are back where we started with traffic jams or waiting in line to get on the road.
Why are more people driving? Unless you just mean because of population growth, but we've always needed to build new infrastructure to handle that, and the next 40 years won't be any different.
If anything, self-driving cars will reduce the (relative) number of cars on the road. Several reasons:
1. Since they will probably finish their journey faster than a human driver, they won't be on the road for as long.
2. Once we hit critical mass of self-driving cars, we can get rid of taxis (and Uber and all that), in favor of calling a self-driving car to come pick you up. These cars won't need to be out on the road trolling for passengers.
3. By the time we have 100% self-driving cars I guarantee you there will be multiple companies that are in the business of automatically arranging carpooling, which will mean more people per car (and therefore fewer cars).
4. We'll still have the option to use busses, or mass transit, like we do today. Self-driving cars might even make those options more appealing; take mass transit to the nearest stop, have a self-driving car take you the rest of the way (as opposed to driving the whole distance yourself).
Also, once we reach critical mass of self-driving cars, we can start exploring other infrastructure options for moving self-driving vehicles around besides surface roads. Remember crazy-looking highways for self-driving cars in I, Robot? I don't think we'll end up with something that looks like that, but that's the general idea.
In the long (very long) run it could solve this problem too - if all cars were fully automated and very safe, they could travel much faster even inside cities, thus augmenting the bandwidth of roads.
I'd argue that they can't go too much faster in cities. For starters, people live in cities and tend to walk or bike places. On a city street with no people walking around, sure, cars could go faster and be safe.
But in a city with people, cars will need to go slower and stop for people (or some combination). Even with instantaneous reaction, a car can only stop so fast.
Of course self-driving cars are the necessary future, but it will drastically increase ridership as it becomes so much more convenient than the alternatives (including being sober/awake enough to drive). Over time I suspect that even the most efficient car system will result in traffic sucking just as much today, except with the option to watch tv instead of the road.
