Hybrid Personal Rapid Transit

When I was in high school, I did a project on PRT -- Personal Rapid Transit. It was the "next big thing" in transit and of course, 30 years later it's still not here, in spite of efforts by various companies like Taxi 2000 to bring it about.

With PRT, you have small, lightweight cars that run on a network of tracks or monorail, typically elevated. "Stations" are all spurs off the line, so all trips are non-stop. You go to a station, often right in your building, and a private mini-car is waiting. You give it your destination and it zooms into the computer regulated network to take you there non-stop.

The wins from this are tremendous. Because the cars are small and light, the track is vastly cheaper to build, and can often be placed with just thin poles holding it above the street. It can go through buildings, or of course go underground or at-grade. (In theory it seems to me smart at-grade (ground-level) crossings would be possible though most people don't plan for this at present.)

The other big win is the speed. Almost no waiting for a car except at peak times, and the nonstop trips would be much faster than other transit or private cars on the congested, traffic-signal regulated roads.

Update: I have since concluded that self-driving vehicles are getting closer, and because they require no new track infrastructure and instead use regular roads, they will happen instead of PRT.

Yet there's no serious push for such systems...

Read on. Most PRT designs require special custom cars with the ability to accelerate and brake very quickly, so the station spurs can be short. You can play some tricks by creating gaps in traffic to allow breaking/acceleration on the main line, but only to a limited extent and with safety risk.

One of PRT's flaws is that it's more like a taxi. People like to personalize their cars and keep their stuff in them. And of course if you are not near the station, you still have to get to and from it, in the weather, etc.

I suggest a Hybrid PRT vehicle, which is also a small electric "city car" like the TM Th!nk or the Smart in size and design. (Actually its size and design are more constrained by the parameters of the PRT track.) This car would have batteries only for modest range (say 10km.)

People would buy these cars, and keep them at home or office with a charger. They would have range for local short city errands, and of course to get to the PRT track and a grade-level entry/exit station. There they could drive into the special station and let the PRT system take control of their car. The car might be driven by providing an electrical connection to run the car's electric motors, and there could also be magnetic induction for the quick starts/stops in stations as needed.

Once the system delivered the car to a station, the car could drive out if it had further to go, or more commonly the passenger would just alight at the station. At that point, some owners would elect to rent their car out to the system. Such cars would have two trunks, one always for the owner's permanent gear and one for any user. If enough people did this, the system may not need to own many cars of its own.

If the owner is a commuter with decent plans for when they want the car next, the car would of course be scheduled to be ready at the owner's stop at that time, or nearby and summonable on short notice. If the owner wants it at an unexpected time, options could include providing a free rental replacement, or requiring the current occupants to change cars at the nearest station, and then whisking the car to the owner. It could be arranged that the car never goes more than a few minutes travel from where the owner is. (Those who want longer trips are just never assigned such a car.)

Other owners would elect not to rent out their car. Their cars would be whisked, empty, to a storage yard (parking lot equivalent) not too far away. A cell phone signal just a few minutes in advance would have the car waiting at the station.

Ideally the standard car size would be built on an existing popular chassis for a regular car, to make production cheap. It's also possible to imagine the hybrid having a gasoline engine. If it's electric, the weight of the battery may be a question. One solution is to have a small battery, with range only for short trips.

Another idea is to have a fancy modular battery system, with automatic machine swap-out possible. The car would be moved to the battery swap station where robot arms could quickly remove the battery at the start of a trip (storing and recharging it). They could also attach (on egress, probably) different sizes of batteries, so those needing to travel far from the PRT system could do so. Like the cars, batteries could be rented out to others. You probably don't need to get your exact battery, but since batteries have life-cycles, this would need to be tracked so it all remains fair.

However, due to the delays involved and the extra logistics, it would ne nice to get the system going without the battery swap, then add it for efficiency and flexibility. If the battery remains in the car on the network, ideally it would be recharged while moving. This does mean a somewhat dangerous high-voltage power system, but modern electronics can make that safe. Also, if cars have batteries, temporary safety interruptions of the power are not a problem. (Totally in-system cars would need a small battery able to get them past power gaps.)

The result would be a transit system people would actually use. Fast, no-driving, non-stop transport (so you can read or work on the trip) with no stops would beat out cars every time for a radius of several km from the track system. The track itself cheaper and smaller than roads or rails. The cars paid for mostly by the public.

There are a few things it can't do, such as readily emptying a stadium. To do this, people may need to walk a bit to get to multiple stations, or traditional multi-passenger busses could take people 60 at a time to a network of stations which can distribute the load. Special stations designed for bulk departure and arrival could also be built.

Rush hour is a problem for all transportation systems of course. PRT might be cheap enough that the system could be built closer to being able to handle the peak load. Instead, at rush hour, people might arrange PRT "appointments" where the track-segments needed for their trip are reserved. If the system is overloaded, they can at least relax and work before going to the station at their appointed time.

It's also worth considering that PRT has a long history of failure, and there are some good arguments about why it's one of those things where theory and practice differ a great deal. On the positive side, technology is rapidly improving (especially computers, and some materials) and we often forget just how much of our land we devote to the real alternative, the automobile. When you consider the true cost of the car, even way over budget PRT (and LRT) sound pretty good.


What is "at-grade"?

There is a bogus link to "solve this".

I'd be concerned about tragedy of the commons aspects. I call for a transport (or get mine back after renting it out), open the door, and realize it's been littered/vandalized/thrown up or urinated in.

One of course being don't rent yours out. Obviously there would be insurance included in rental fees to cover the costs of that. While I would be opposed to mandatory ID for rental (you don't need ID to take a Taxi after all) one could still have non-linked rental cards (filled with cash) which have a reputation, and you could agree to rent only to people of a certain reputation. People would no reputation would be limited to renting "system" cars with higher insurance rates.

The wealthy would probably not rent out their cars at all, or perhaps rent them only to 'clubs' of trusted people. But that's still a lot better than today, when our cars sit in garages almost all the time, doing nothing and using garage space. Others, who could never afford to buy a car for themselves, could do so by being willing to rent, and take the risk.

Sounds like a solution for people who like the idea of socialised transport but fear contact with others. Then there's the huge cost of a duplicated road network to carry them. Why not just add bike lanes and use real PT like buses and rail?

But public transit averages about 12 mph because it stops all the time, and switching lines on a PT system can often take a lot of time, worse if the schedules are unreliable. Surface transit of course also hits traffic like cars.

The PRT idea was conceived long ago. Today there is some argument that self-driving, crash-avoiding cars may realize this vision on ordinary roads.

But the big plusses over both transit and taxis are the fact it doesn't stop, you rarely wait for it to arrive, changing lines is like changing highways, and it has private right-of-way to avoid traffic. Compared to the car it also does not have to be driven, so you can work.

The proponents also say it's considerably more energy efficient than transit, primarily because it doesn't have to start and stop all the time, and while there is waste sending empty cars around to new stations, you don't spend most of the day with large underutilized train cars and busses like transit does.

That's the theory, anyway.

But because transit gets such a low net speed (measured in average trip time, including waiting and stops) for short-haul in particular, the PRT doesn't have to be very fast to beat it handily. A 20 mph PRT would typically beat street cars and busses as well as ordinary cars in anything but light traffic, and even private right of way trains if there's wait times or line changes.

Compared to 12mph for trains, private motor vehicles are often slower than 10mph and even slower if you count door to door times rather than only "time on road".

In my experience (Sydney, Australia mostly) once you include waiting time the trains don't even get to 12mph over short distances. But for non-trivial distances (anything over 30 minutes) the average speed here jumps dramatically thanks to express and station-skipping trains (we have >4 tracks on much of the network). For longer journeys trains make a lot of sense, especially since I can take my PRT on them.

But then my personal transport weighs in at about 100kg all up. I have 5 bicycles, you see and I already have personal rapid transit. When I can't ride my bike I often get quite impatient as I'm not used to waiting and going slowly for no readily apparent reason, since bicycles are fast, door to door and if you're in a hurry it's legal to go as fast as you're physically capable of (for the most part). The cost also doesn't bear thinking about, especially if you're a motorist. I trust you're familiar with Ivan Illich's ideas?

There are a lot of ways to measure trip times, and thus average speed, and they vary a lot depending on the trip. There will always be debate over what is fair. For example, a car leaves when you want it to, a train may only leave every 30 minutes. Should we add an average 15 minutes of wait time, or figure that people just alter when they will leave based on this. (Once transit gets to about a 5 minute interval, people start to ignore schedules and just leave when they want.)

For those who aim for a specfic train, we must add time for when it is late. Any time you have a transfer, you must factor in not only the typical wait time but the occasional risk of a missed connection.

This (like traffic jams for cars) also affects the other thing people care about -- standard deviation. For example, if the train usually takes 30 minutes, but one time in 5 it takes 45 minutes, then if you have a hard deadline to hit you typically must plan for it to take the 45 minutes (and accept the consequences of lateness if it takes 50.)

This is a killer when trying to hit really hard deadlines like plane flights or infrequent long-haul trains. Unreliable transport to the airport forces you to allocate a huge time for a trip that might actually have a short average time.

Of course, dedicated right of way is great for making the time reliable, as well as improving the average time. I suspect the reliabilty of dedicated ROW is more important than the speed gain. This is one of the things that attracts people to PRT over cheaper and better established at-grade light rail, or even dedicated ROW light rail that still has to deal with traffic lights.

It's possible that the real solution will be the arrival of crash-avoiding, self-driving cars as PRT, using existing roads with some special privileges (such as private lanes.). But until those arrive, people will focus on other systems.

Learn more about the PRT scam at the PRT is a Joke web site.

Dump Representative Mark Olson (16b)

Is even more rabid and hype-overloaded than what you accuse the PRT-backers of being. You would do well to rewrite it.

There obviously are problems in front of PRT. I don't think it's entirely crackpot, because take a look at the alternative and how crazy it sounds:

  • Almost everybody will buy and maintain a huge complex machine weighing 2,000 to 6,000 pounds and costing several tens of thousands of dollars
  • In addition, almost every dwelling will, at large expense build a room to house this machine, usually with automatic door and a paved path from the road for it.
  • Every office and shop will have a giant lot or structure for these machines. In addition, in most places, 10 feet on the side of each street will be allocated to storing the machines.
  • All told, between 35% to 60% of our land area will be devoted to streets and parking for these machines!
  • A major component of our air pollution comes from these machines, up to 90% of CO, 20% of CO2. People die daily from the particulates. Wars are fought over the fuel.
  • Each machine is used briefly for a few trips, then stored for the rest of the day.
  • Each machine requires an individual human to handle the rote tasks in controlling it while it is in use, time that could be spent working or reading
  • Some shared machines (Taxis) exist but still require a human to operate them.
  • The machines kill 42,000 in the USA every year, far more than wars, terrorism, guns, falls, poison or in fact any other non-disease reason.

You have to admit, a system like that sounds insane, far more insane than PRT for the problem of inner-city personal transport.

Mass transit sounds better but in fact because it involves long waits, long transfer times and big giant vehicles running mostly empty outside of rush hour, it sometimes isn't much more efficent in cost per passenger mile and people pick the car over it in almost all wealthy cities.

Really. it is a total time-waster.

PRT will happen - when it becomes fiscally viable for people and companies to invest their private dollars into the entire ifrastructure of such a system - from producing the actual vehicles, to the rails, stations, hardware and software to make it work - so long as there is a profit. Large corporations can pool resources and capital to build the actual system, with the expectation of a use based fee as their payment for the amount you use it. These same companies and others can mass produce (for low cost to the consumer) or even custom make the vehicles, again for a profit. Owners of the vehicles could at their discretion rent out the vehicles when they themselves are not using them - either for a profit (e.g.: people with large sums of money to invest - say a highly paid doctor or engineer or real estate investor, or a blue collar guy who can make the numbers work and get a loan - can buy small or large fleets of vehicles to be out for rent as a business) or the average user can simply allow theirs to be rented to help defray the costs or ownership. The vandalism issue could be minimized by charging enough to cover insurance, graduating rental fees based on some type of preferred status, renting only to known persons or "clubs", and heavily protected cameras that record users as a deterrent and for prosecution after the fact(my cars would require renters to accept surveillance - perhaps others would not reguire it, but they could of course charge more for the privacy; free enterprise would regulate such a system).
In the end, once the technology becomes cheap enough for a return on investment, this kind of a system will be born.

The anonymous person who posted the link to the anti-PRT site ("PRT is a Joke") is Ken Avidor, who is a rabid anti-PRT extremist. He spends all of his free time hunting down any discussion of PRT and injecting his anti-PRT propaganda. Most of what he presents as "evidence" is nothing of the sort - just various political rants and conspiracy theories.

Take everything this guys says with a grain of salt.

For a more balanced discussion of PRT, see the PRT Wikipedia article.

..people like this guy.

Here's the transportation of the future, PRT--Personal Rabbit Transit.!!!

Since Avidor brings it up, check out the Wikipedia PRT Talk Page, where Avidor tried his best to fill the PRT article with his anti-PRT propaganda message.

It got pretty heated on those pages, as we defended the facts in the article from Avidor's vandalism. But, in the end, the article survived almost completely unscathed - because the facts about PRT are indisputable.

In fact, I think it's a much more solid article now that it has survived an attack from PRT's biggest critic. I like to think of it as "battle hardened".

By the way, the Wikipedia article also touches on "dual-mode" PRT, which seems similar to Brad's "hybrid" ideas.

I think there are valid points on both sides. Overhead lines in dense city streets are ugly be they monorail, PRT, or elevated rail. Capacity (at rush hour, at train stations and stadiums) is an issue. It is yet to be proven. But those who say something is impossible because it hasn't been done yet are too extreme the other way.

The dual mode concept (which is indeed similar to the concept I outline, though it predates the idea of electric cars and the ability to charge and control them on the line) has a number of advantages in terms of adoption. In particular getting the people to pay for the cars, and having the system only build the infrastructure is less of a leap from today's system.

Classic PRT would have no problem getting adopted in a city where most people are used to not driving (taxi/transit) but may not fit as well for environments where people insist on driving.

Though I generally think, based on the speed at which transit systems develop new ideas, that it's more likely we'll see crash-avoiding self-driving cars on the regular roads, because we already have the regular roads and they aren't going away any time soon.

We could actually have self-driving vehicles on specially prepared roads (guide wires and signals etc.) but we can't deal with what happens if a pedestrian or ordinary car gets in the way.

I was trying to imagine what you could do with one-way guideway down the center of existing roads with a concrete barrier around it (costing a lane, which is recovered from street parking spots no longer needed.) But you can't have barrier in the intersections. To make this work you would need long red lights for the cars -- and deliberate long gaps in the PRT slots for when the cars get green lights. For "stations" passengers would have to take the controls of the vehicle in special exits from the track and manually take it to the station (small parking area), and then manually bring it to a track entry point.

But the cars could still hit a pedestrian or other car in intersections, and it would mean nobody could left-turn out of driveways along the streets.

The problem I have with dual mode is, it doesn't solve the parking problem. One of the benefits of PRT is that the vehicles are reused, but if you have privately owned vehicles on the guideway, you still have to have places to park those vehicles.

Clearly many people will rent out their vehicles if they have a station near their home or work. For a large chunk of the population, it would mean the difference between owning your own vehicle at a price you can easily afford, and always renting.

However, for those that don't, you need parking, but you don't need it really close to the station. (Though the closer it is the more quickly you can summon it on short notice.) You can park somewhere that the parking is cheap, and you can park the vehicles very densly compared to cars, with a slight extra delay. Probably 3-4 times the density of cars if they are smaller and can also be stacked vertically in spots 6' high, and like valet parking.

For the commuter who knows they need their car around 5pm, the system can prep the car in advance and have it waiting at the station. However, for the typical office worker, you would issue a computer/cell command when preparing to leave, and in the typical 5 or more minutes getting in the elevator and walking a short distance to the station, the car should be very close to being there, if not there already.

Office buildings might also build large "parking stations" in their buildings, using some of the space that was allocated to cars. As noted, I expect at least a 3x density improvement, and this gives a station in-building with instant access to your vehicle.

There's also another kind of "rent" possible with vehicles, namely within the family. Car takes parent #1 to work, returns to home station (though not to home garage quite yet) for use of parent #2 or kids or whatever. And kids of course can mean even young children if they don't leave the automatic track area. Those kids can probably bike to the station, for example.

Denver Airport Luggage system. A "PRT" for luggage this MASSIVE FAILURE is well documented by many scholars as a famous engineering cock-up, like replacing the air traffic control system, and the FBI computer systems.

United Airlines dumped 186 million US dollars in debt on the public by
declaring bankruptcy and threatening to dump Denver as a hub unless the
public was to eat the debt on the luggage "PRT" system after they shut it
down as a drain on resources. It cost a million a month for the luggage
eater to run and also cost United its baggage handling reputation.

It has all the earmarks of a PRT project. guideways, autonomous pods,
on demand service, scams, techno-hubris and, of course, not working.

Proponents always say the same thing of PRT failures: "that's not REAL PRT."

Invariably, once Avidor starts posting his propaganda campaign, he won't stop until he spews his entire spiel.

This latest rant falls under the category: "PRT projects failed in the past, therefore PRT can never succeed in the future". Avidor has recently latched onto the Denver baggage system because it failed so spectacularly, even though the Denver baggage system has nothing to do with any PRT design I've ever seen. But Avidor doesn't care if it's relevant -- as long as he can use it to scare people off PRT.

Even if the Denver baggage system is considered PRT (it's not), it's still a ridiculous argument! If every technology was killed after the first few failures, we'd still be riding horses!

PRT has nothing to hide. Past failures are well documented at the Wikipedia PRT page. The reasons for the failures run the gamut: poor design, poor engineering, economics, politics - all things that can be fixed.

Go ahead and decide for yourself.

I am not Avidor. I am an opponent of "faith based transit" quackery and scams such as PRT. Face it, pal, PRT is a discredited technology. Only hucksters and suckers are left in the PRT biz. Denver Airport baggage handling has you beat. And you know it.

Mr. Anonymous: You are quoting almost verbatim from the Avidor creed, right down to his buzzwords like "faith based transit". So you are either Avidor himself or one of his apostles.

But, anyway, who says it is irrelevant -- the point is, this is the same tired old message that Avidor has been pushing for years now. These points have been discredited countless times on dozens of forums, but he remains obsessive about continuing to spread them, like gospel.

If you want these types to go away, just challenge them to a debate on a technical topic, like PRT safe headway. They'll spout some ridiculous talking point and then disappear with an excuse ("I don't have time to debate this crap"). I've seen it so many times I can almost recite it by heart.

Anyway, if you don't believe me and want a neutral assessment on PRT, once again I suggest you take a look at the Wikipedia article. There is a very nice technical summary there, along with many links to the history of PRT development.

I came up with "faith based transit" and many people liked the phrase, apparently Mr. Avidor likes it too. That is OK, it fits PRT and is now a PRT synonym. Mr. Avidor does not come up with all
the great sound bytes. He is more a visual artist.

The Denver Airport Luggage Handling Fiasco (PRT for suitcases)
is the engineering lesson that civil engineers and city-county-state officials will recognize and pay attention to, a public investment of hundreds of millions for many years that was a complete failure that cost the public huge losses.

No civil authority will put reputation, public safety and
financial ruin on the line for this Jetson cartoon fantasy after looking at the history of the Denver Airport PRT luggage handler.

PRT is a dead technology.

There is a fundamental point you seem to be missing: the failure of one engineered system does not invalidate the underlying technology. The Denver baggage handler was a dismal failure of design and engineering -- it does not mean that all automated systems will suffer the same fate.

Here's a classic example of spectacularly bad engineering, with a truly catastrophic result. Does this incredible failure invalidate all bridge designs? Of course not! In fact, after the collapse, they redesigned that bridge and it's stood for over 50 years.

Your argument is inherently technophobic, and it has no relevance. I'll say it again: the Denver failure was a failure in design and engineering, and has no relevance to the underlying technology.

And, by the way, if you want proof that automated, PRT-like systems can work, look at Morgantown: automated operation for over 30 years. And even though Morgantown is not true PRT, it's closer to PRT than Denver's baggage system.

See Wikipedia for links to the Morgantown system -- again, not true PRT, but neither is Denver's baggage system.

I think it's fair to say that failures at certain tasks suggest those tasks are harder than people imagine. They are certainly a reason to be wary and to look harder, and to learn the lessons from a failure. But they don't prove something impossible.

On the other hand, it can also be foolish to assume that the reason everybody before you failed at something was because they were all stupider than you. Sometimes that's true but not always. The baggage system was not a PRT, but it contained some technologies people want to use in PRT. Certainly a working PRT system could be easily reworked to deliver bags to destinations as readily as it delivers people. Probably too expensive a way to do it, though. Deliverying people should be much more expensive than bags in almost every way, and cheaper only because people enter and leave the cars under their own power.

"On the other hand, it can also be foolish to assume that the reason everybody before you failed at something was because they were all stupider than you."

There's no assumption here. When systems fail, engineers analyze the reasons why, and fix them in their future systems.

I've done some reading on the Denver system. The issues were primarily poor engineering. For example, the bags had to be loaded onto carts a certain way, or they would fall off on the curves. This was poor design: either the carts needed to be better engineered, or the curves should have been less severe.

In some ways, I think the fact that it was baggage, not people, actually hindered the design. If they were designing for humans, they wouldn't have designed a system so fragile.

I've read a lot on PRT, and I've seen nothing about it that is technologically infeasible. There are certainly engineering challenges, but many of them have already been solved. All that remains is some field testing and a commitment to build.

In other words, the main issue that PRT must now overcome is public acceptance, and that's turning out to be the biggest hurdle, by far.

At the dawn of the motor age, many municipalities steadfastly refused to accept the new vehicles on their roadways - passing laws against them for all manner of reasons: the unproven technology, the noise scaring horses, the excessive speed, the smoke, whatever they could come up with out of unreasoned thinking. Same goes for heavier-than-air aircraft; many thought the technology would never reliably work and carry people safely and efficiently. Heck, the use of a radio in a vehicle was once illegal in many states when they began to be incorporated into production. Not to mention that at that same time, 25 miles an hour was considered a hell of a speed. Can you imagine going back in time and telling people that cars in the future will easily attain speeds in excess of 100 MPH, and that we would be regularly driving as fast as 60 MPH with other vehicles traveling in the same and opposite direction at similar speeds without any barrier between - down to sometimes as little as one foot apart. If you were to share this with people from the past, you would surely be rebuked and ridiculed and run out on a rail, same as rabid anti-PRTer's do today.

I suspect the animosity results from a fear that PRT would become yet another government enterprise like regular public transportation: incapable of becoming self sufficient without continous taxpayer subsidy. On this I would agree - I also don't want socialized, subsidized transportation. However, today's road and highway system surely isn't self supporting either, being funded in large measure by tax revenues which are not based in any form by actual road usage (true, gas taxes are use-based, but the larger remainder come from income and property taxes). I'll state it again: when private enterprise can support the construction and maintenance of such a system (you and I as individuals are a part of private enterprise) without taxpayer funding, this kind of concept will flourish - just as it has for the automobile industry in years past.

Technology that works usually gets started right away, planes for instance, 20 years after the Wright brothers they were all over the place. Radio, computers, telephone, trains, this is an example
repeated over and over. See the pattern?

PRT and blimps on the other hand are a bit limited in acceptance and
availability. Shriveled tendrils on the branch of tranport evolution.
DEAD TECH. No hoping for the next "breakthrough" is going to make
PRT work after 40+ years. WVU Morgantown is the goodyear blimp
of PRT. Kind of works, but cost a mint, and does not really work, with limited service and a captive audience.

40+ years is a long time for a tech to "almost" work.

They cannot argue on technical merits, so they argue that "it hasn't worked for 40 years, so it never will". It's pure propaganda.

Judge PRT for yourself, here

Anonymous stated:
"Technology that works usually gets started right away, planes for instance, 20 years after the Wright brothers they were all over the place."

Yes; 20 years after the Wright's, planes were everywhere. But your observation misses the preceding 400 years at minimum of mans' attempt to get heavier-than-air vehicles to work. I can start with the drawings of at least da Vinci; perhaps there were even older plans for flying craft. Yet persistence over all this time, coupled with incrementaly advanced technology over succeeding centuries, and despite MANY tremendous failures (and self-rightous naysayers by the dozen), have given us the ability to cross the world's oceans in mere hours. Clearly, the technology did not work nor get started right away, and yet here we are using it to great advantage nonetheless. Pick any advancement technologically, and I'll bet the same can be said about it.

About 6 years ago, I had a private musical instructor who was highly doubtful of the power of the internet to do anything worthwhile. Yet here we sit discussing the finer points of the persistence of man to overcome obstacles to create the world in his vision, using the internet. And I'll bet Jeff Bezos would disagree with my former instuctor, not to mention the untold number of people making use of Ebay.

Furthermore, I will also mention that anyone of great success will tell you that failure is the path to success. Edison, Trump, Kiyosaki, Tesla - you name it. Today's failure is a kernal of truth, a moment for reflection - "why did this fail today, and what can I do to fix it the next time?" Edison tried over ONE THOUSAND different ways to make the concept of a lightbulb a reality. He did not stop at iteration 2, or 10, or 138. He continued refining his materials, technique, and technology until he made it work! Continuing in this vein, I would also like to point out our (U.S.; western) concept of government as envisioned by the Founders. A limited constitutional republic, which has been the bright light for the world for over 200 years. It can be argued that governance is a form of technology, and yet after all of these 200+ years, there are many nations out there that haven't accepted this form organization, despite what most of us would agree (yeah, it currently has some ugly bugs, but still...) is the best damn state of the art for freedom, prosperity, and individuality there is. Your line of reasoning, in essence, would therefore consider our freedom a "failure" since it hasn't become as widespread or as "free of flaws" as you would like to see.

You're kidding, right? The history of inquiry into manned HTA flight goes back at least a millenium. The 19th century is riddled with manned flight failures, and Lord Kelvin even went as far as to assert that heavier-than-air flight was impossible, and that we should just focus our efforts on lighter-than-air flight, which had been successful for millenia. Much like some would have us focus on centuries old ground transportation technology rather than investigate a new one. Lord Kelvin, of course, was proven wrong.

It took a century or more (depending how you count--much longer if you count da Vinci and the like) to achieve manned HTA flight. We're only 40 years into this PRT thing, and we're likely to see a successful albeit small-scale system at the end of '09. According to the above critic's timetable, that gives us until 2029 to have the technology fully developed and deployed on a large scale. I have a feeling we can manage that.

This is the first time I've seen a site like this. I've been pondering a system like this for years during long commutes but didn't realize it had a name or following.
The question I have is how do you prevent these vehicles from blocking main lines when you have 50 to 100 (or more) people requesting their individule cars at one time/station? I presume that you would load people on a side spur then wisk them away to the main track(s) but when many people want to leave from the same terminal at the same time (such as with current mass transit) it seems to me that there would be a stack up on any given spur and then a major bottle neck to the whole system since this same scenerio would be occuring up and down the line. (I've enjoyed this discussion and would encourage nay-sayers to put their energy to solving problems rather than tearing down other's ideas!)

This is called, I believe, the "pulse" problem, where you get an extreme surge of demand. In general, there are two scenarios to consider:

(1) The typical rush hour rush, where people don't all leave work at the exact same time, but there is a general rush between the hours of 4-6PM, peaking on the hours. For line haul systems, people from a relatively large area aggregate and wait in the station; they don't all arrive at the station simultaneously, but they depart simultaneously because during the wait for a train, the station fills up. So the pulse in this case is not as severe as it would seem: the "pulse" in the station is actually due more to aggregation of people waiting for a train. In the case of PRT, there are two significant differences: (a) people arrive and immediately leave, so there is little aggregating. Some may have to wait in a short line during the heavier times, but with good design this is generally shorter (in the average case) than waiting for the next train to arrive. (b) PRT designs generally have more closely spaced stations, so the load is more spread out. Instead of, say, 1000 people arriving at one station in 15 minutes, you have 250 people arriving at 4 different stations.

(2) True "pulses", i.e. after a sporting event. When you have thousands of people exiting simulataneously from a sporting event, this is an extreme pulse that would place demands on any system (light rail, buses, cars). That's why there are traffic jams after sporting events, because the road system can't handle the pulse. PRT designs I've seen would handle this by building several larger stations at the statium itself to handle the anticipated loads. In other words, a stadium is where you'd expect to handle large crowds, and you'd also assume that a stadium would have the space to allow for several larger PRT stations. So there are ways of alleviating it, but there will still be delays after a sporting event, just like any other mode.

This is considered one of the difficult PRT challenges. A baseball game is even worse than a train station. You could have a very long spur at a high capacity station, or even a spur with its own spurs where cars can presumably move in and back out. You would also have to have fancy algorithms to create gaps in traffic going past the big station to accept all the traffic. Ideally it would leave in bunches, sort of like trains but uncoupled.

Or you would of course, have to have long waits at such stations from time to time. Which is what we have now with shared transit, after all.

PRT people say dozens of vehicles can go around dozens of rails under computer control. If this is the case, why aren't there been many, many cases of single vehicle, single rail projects are being computer controlled? After all, computer controlling a train going back and forth on a single track should be EASY. That would save money, right?

Not even this is being done, but somehow the PRT True Believers tell us the much more complicated case is the next step. Shouldn't they be able to point to successful computer controlled trains all over the place if they are that great?

A freeway lane can be converted to a PRT or GRT lane at minimal cost--just the cost of track and some barriers to separate it from auto traffic. Freeways provide already-existing grade-separated rights-of-way, which is most of what makes PRT cost so much.

The issue there is whether the pubic would tolerate giving over freeway lanes, which they view as precious, until the new system has reduced the need for the lanes -- which it can't do until it's been running. In fact, it may have a harder time then that, as it's been shown many times that freeway traffic tends to expand to fill capacity fairly quickly. As a counter, it also reduces in response to reduced capacity. But try convincing voters of that.

I suspect it's more likely to see highways used as easy ROW for adding elevated traffic, or possibly highway medians, especially if they are wide enough. Of course in this case you must have elevated or underground track for entry and exit.

Add new comment