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PRT is pretty much an expensive scam. There are no working system, and there's a good reason for that. It requires all the infrastructure expense of rail, for a system with a capacity not much better than cars on roads. And most of these systems run on rubber tires, so they're about as energy-efficient as cars, but without the flexibility to actually go everywhere in the way a car can. So yes, it might be possible to replace New Jersey's bus and road system and cover the whole state with PRT, like in that study. For only a couple trillion dollars. That's $2,000,000,000,000. That's a whole lot of zeros.
Actually the studies by Vectus and ULTra show they get 254 watt-hr per mile. Cars use about 1500 watt - hr per mile. Where did you get the $2T number? I'm using $10-20m per mile.
Potentially inaccurate back of the envelope calculations, but if you want to cover all of New Jersey, then you're going to need a whole lot of miles. Because the premise of PRT is to be both the mainline and last mile transit option, and it take quite a lot of miles to get near enough to everyone. Oh yeah, and there are going to be major capacity issues using this as a mass transit system. It could potentially be useful on a local scale, for example, going around some suburban office parks and linking them to a mainline rail station. But at some point it's just a better idea not to build suburban office parks at all and replace that travel with walking to buildings located much closer to transit.
Oh, and about the energy efficiency numbers: the number for cars is based on real cars running on real roads. The numbers for PRT is based on imaginary cars running in the heads of the designers. But the fact that it's electrically powered does give it a bit of an advantage over cars, at the cost of having to build an absolutely vast amount of infrastructure.
Efficiency is better than cars but the commuters experience is the big seller. Getting people out of cars is a difficult sell and we need to be creative. The engineering issues for PRT are difficult but solvable, I'm not sure you can say the same thing for batteries. Any amount of car pools, van pools and fossil powered hybrids will not meet the IPCC targets. Electric grid powered vehicles are the right direction, we just need to figure how the cheapest way to do it. Heavy and light rail form the backbone and for the rest the options are: 1) buses (or cars) with overhead wires in hilly areas 2) buried cables (induction) or 3) PRT which solves the slow transit time issue.
PRT doesn't solve the last mile problem, the goal is to put a station within 1/2 mile of everyone. If the station servers 2-4000 people than you need a population density of 2,000 per sq. mile. Low density suburbs should be converted back to farms. Everything else should get some kind of rail system. One station every sq mile is quite reasonable and the study has a good map of how counties should be configured.
I just don't see any field of application for PRT. If you want local low-density transit, you use a bus, or a trolleybus if you want to power it off the grid. The density justifies it, if you assume there are no low-density suburbs, and it's a hell of a lot cheaper to build. As an added bonus, the roads it runs on can also be used by cyclists, and generally come with sidewalks that can be used by pedestrians. No expensive elevated structure required. And if you have higher density, you build a streetcar, or light rail, or in extreme cases, a subway.
Oh and about PRT efficiency. If you want "push a button and the car shows up" service, then you're going to need a reserve of PRT cars. Many systems assume that these empty cars will just be circulating throughout the system. That already lowers your efficiency, potentially significantly. Then there's the issue of headway. If you assume a railroad-style safety model with one braking distance between cars, then headway will end up at something like 30 seconds, meaning the line could transport something like 150 people per hour in ideal conditions. If you assume a car safety model, without a safe stopping distance ahead of each car, then you can get the headway down to, say, 5 seconds, and get a slightly more respectable capacity of 800 people per hour.
Now let's consider what happens at the interface between a real transit system and PRT. Suppose a light rail train arrives, and 25 people get off. They'll be getting into 20 PRT cars, because most people will want to ride alone. Suppose it takes about 15 seconds (and that might well be an underestimation) for each to enter their destination into the system and board a car. That's a total of five minutes just to clear the station if you have just one departure track. And if even a fairly minor light rail station requires a 2-track PRT terminal, imagine an urban subway station with 100 people getting off each train every five minutes. Then you'd need a five track terminal, which is getting to be large and intrusive.