Saturday, August 15, 2009

46> Many Vehicles, One Track

Here’s something to think about. In this picture, the vertical blue lines represent payload capacity, something like 50 to 75 kg per line. I originally started drawing this picture to explore weight distribution of possible track compliant vehicles, but then I realized that I had better share a bit of thinking first.

The baskets (A) represent something that could be used in manufacturing or for baggage handling. It’s not PRT, but it is a possible avenue to a proving ground and test track. A successful system would be a great confidence builder for the hardware, software, and the company that installed it. Having a demonstration project (that you get paid for) seems like something worth considering. (Currently the “state-of-the-art” technology involves conveyor belts or other floor space intensive systems, with laughable forking and destination sorting technologies.)

Cargo containers (B) can be similarly used, including outdoors or across town, if necessary. Cargo can be loaded and scheduled to depart automatically, so it can travel in the middle of the night, eliminating the cost of drivers working nights or being stuck in traffic in the day and, naturally, saving gas and payroll. Cargo containers could also be programmed to take the “long way” to their destinations to reduce network congestion, (for a reduced rate, of course). These would be great for moving mail between substations, for example.

The small “pods” (C) represent what would be best for 95% of rides taken, being designed for two or less passengers. These small vehicles could be pretty fast, passenger profile permitting, and would therefore be competitive with cars for longer commutes time-wise. Although current models generally assume identical velocity, these models also assume very limited networks. It should be noted that no system will be full of vehicles 24 hours a day, and that in a more comprehensive network, routes can be dedicated to faster or slower traffic dynamically.

The full size “pods” (D) can be used for families, people with bikes, baby carriages, the disabled, people with luggage, etc. These would have the “standard,” more gentle and slower ride, and employ greater headway between vehicles. Because there are societal benefits to traveling with a bike, or traveling in groups, or enabling the disabled, etc., I think that this class of vehicle should be subsidized and be more numerous within the network than ridership statistics alone might dictate.

The last, labeled (E) is a GRT or “Group Rapid Transit” vehicle and is designed for downtown or shuttle environments. It cannot ascend or descend steep slopes, and is designed for more expensive, high capacity stations. It designed to run profitably in simple loop or “back and forth” configurations such as between airport terminals, and, most importantly, could get the first PRT compliant track built. GRT can skip stations without passengers, like a city bus, but it can also have the intelligence to coordinate with other such vehicles to match passengers and destinations. This, and their small size, compared to buses or trains, means that no passengers have to sit through more than a couple of quick stops. After more loops are completed PRT vehicles can be added as needed, and the GRT vehicles retired or converted to night delivery use. (Or perhaps they will be found to have continuing utility within the system. I am not aware of any studies involving GRT and PRT sharing track, and really have no opinion, at this time, one way or the other.)

Most people are linear thinkers. The linear thinkers among us will see all of these vehicles as a hopeless distraction. I, on the other hand, usually look forward and imagine an optimal embodiment and environment, and then backtrack from there. This enables a viewing of possible pathways to a desirable outcome that cannot be had otherwise. It’s like cheating at solving a maze by starting at the end, so if I seem to fluctuate, sometimes, between reality and sci-fi, that is the madness behind the method…I mean, “the method behind the madness.”


cmfseattle said...

maybe we should ask them to build a real PRT system. they could use a slam dunk, what with the 787 headaches of late.

sometimes i wonder if cabintaxi's larger vehicles were a mistake; hamburg ended up just installing streetcars.

Bengt Gustafsson said...

Swdetrack's FlyWay system was designed with a quite large track (inherited from Siemens' H-bahn) and allowed different vehicle sized. A lot of interesting information is still available on

Nominally this company is still in existence, but I don't think it likely that they be revived and start building anything at this point.

Personally I think that all vehicles need to be able of the same movements. Otherwise the entire network will have to be designed for the worst performer (when it comes to grade taking, tight turning, speed, acceleration etc.). This downgrading would make the better specs of other vehicles mostly useless as there will always be some slow vehicle first in the queue...

Also, a mixture of vehicle types will make stations much more complex or require vehicles to "get out of the way" to let the requested vehicle pass. This will lead to additional, unnecessary, guideway load.

Ollie Mikosza said...


I am convinced that having a mixed vehicle fleet is a bad idea. And mixing GRT into it even worse. What for?!

PRT system delivers more capacity than need outside of peak time, and during peaktime we can move 50% of people without wait, with other 50% having to wait 1-2 minutes. So why create GRT problem, which will not deliver more people faster to their destination, as they will have to stop on the way. And the costs will be exponential, because your beam will have to be 2-3 times havier and 10 time more expensive.

And as for mixing container and big/small vehicles it also adds a lot to wait time and fleet complexity.

It is much better to have one type of vehicle with 4-5 seating or 1 wheel chair and 1-2 persons. And the same vehicle can move container with 400 kg payload, since 99% of goods moved within city will fit into it.

Anyway, this is what MISTER will do. But good luck with your strategy :)


Dan said...

Dan the Blogger responds-
Hi cmfseattle,
I did not know that Boeing did the Morgantown PRT. I do not know much about the Cabintaxi or Morgantown systems. If they both carry groups, do they actually change routing substantially, taking shortcuts, or do they just operate like a horizontal elevator, or driverless bus?
I haven't checked out the videos yet, but I've got my son coming in from out of town, and will be pretty busy for a while.

Hi Bengt, Hi Ollie,
I would address your comments individually, except that your points are very similar, and I might make my next post about this anyway. One quick point. As I mentioned, my conceptual explorations are not in an ideal world or timeline. I do not pretend that all of these vehicles should part of a business plan.

A “worst performer” should never hold anyone up. I think we all agree on that. The standard speed should be as fast as a disabled compliant vehicle can go without making the passengers feel uncomfortable. (motion sick) I do not, however, see any reason why passengers who are traveling alone in the night and never get motion sick shouldn’t be allowed to go faster. This is purely theoretical, of course. In practice, no companies are going to want to add complexity to their systems without a very good reason. I would point out, though, that just before rush hour, drivers tend to go substantially faster, and this is a good thing, as it clears them from the “system” before it bogs down. I would imagine, many years down the road, someone will contemplate a similar strategy for PRT.

As far as the GRT, it weighs no more than the pair of standard vehicles (D) shown to its left, and requires no special track. Obviously it isn’t compliant with your station design, Ollie, but that is another subject. The real reason I included a GRT was to provoke thought. Specifically, how many stations does it take to make PRT worthwhile? Cities don’t want to test a new transit concept with 50 kilometers of track and a hundred stations. They want to start small. But with a simpler the track layout and fewer stations, the advantages of PRT become less clear. For example, with only 3 stations arranged in a triangle, it would seem to me that GRT would be a better choice. When, exactly, does the case for PRT become compelling? 4 stations? 6 stations? Or is it more about the track layout? Anyway, when I get some time, I’m going research the matter further.

cmfseattle said...

I think it's the number of diverging paths (rather than the number of stations) that makes PRT worthwhile. I haven't visited Morgantown, but I've heard that you sometimes have to wait around for an empty car's doors to open.

basically, each junction would need to also be a transfer station.

I think if I were designing a GRT system, I'd spec Flyda's hubs-and-spokes (scroll down about halfway), but using Urbanaut components.

Mina said...

The problem with larger cars is that they demand that all riders are going to the same place – that's why Morgantown isn't a good example: in Morgontown everyone is going to the same place because the system isn't big enough to allow much selection.
One of the benefits of larger cars is that sometimes you're traveling with a group – for example when you have kids, or you're taking a client out to a business lunch, or you need a car big enough to fit your bike into. How about if we keep all these sizes and have a class rating that defines parts of the track that each type of car is allowed to travel on. That way we can have the best of both worlds, track that can be small enough to go through tight spaces (even through buildings) and cars big enough to accommodate what ever people want to use them for; all we need is a control system that recognizes the dimensions of both car and track and enforces reasonable rules.
Rather than a standard carriage, we need a standard connector that allows different manufacturers to add cars to the system. That's what makes an open standard powerful – getting competing companies to work together on one even playing field.
I think the key to this whole thing is to define a standard attachment method that allows various manufacturers to create any old carriage they want.

Mina said...

Defining a standard, interoperable connector for attaching the carriage to the boughie also helps address the issue of controlling the pitch and yaw of the carriage; basically it puts the issue in the hands of the carriage maker to address any way they see fit. If the manufacture is making a carriage designed for cargo, they can skip worrying about passenger comfort entirely. If some other manufacturer wants to build a carriage designed for opulent comfort, they can develop some fancy patented doodad to predict which side of the car has the fat person and what to do if they reach for a cookie.

Banked curves are designed with both weight and direction of movement in mind, but our assumption is that these two things will vary significantly with each trip. I say “don't bank the track – make the carriage do the work”.

We should inform the control system of the weight and dimensions of each car traveling along a length of track and then let it determine the maximum speed for the car based on the curves in the route the system choses. If the car is too big for some sections, the control system should be able to keep it off those sections of track.

I'd like the track to have sensor check points that allow it to verify the weight and size of a vehicle, but I don't think it's really needed. I'd like the system to be able to charge riders based on weight added to the car etc..

I assume that once the concept is proven, this system will take off like the internet, and then we're going to suddenly see that some users have a vary voracious appetite, so a need for user controls will arise.

Dan said...

Dan the Blogger Responds-

Cmf – that Flyda system is compelling. There is a similarity to the Mister design in switching, which I like very much, maybe better than my own approach. (I’m going to have to post on the pros and cons at some point.) I never found the reference about hub-and-spoke, though. I like the Urbanaut rotary switch, which would work on my captive bogey track, but not the other. I have to prefer “in vehicle” switching, for the most part. The crossings allowed by the rotary switch would be very good for indoor warehouse and factory or airport use. I’m not sure about people.
As for the Morgantown thing, well, it’s pretty old. Boeing should make it sing for the good will.. Do you know about the Denver Airport fiasco?

Mina, Thanks for weighing in… I completely agree with you, to a point. The idea of breaking down a big project, system, chain of command, whatever, is just good business sense. I also agree that a mechanical division at a point above the suspension is a good choice, for the reasons you site. Bengt, (from Beamways) also has put time into the idea of a standardized connection for this area, though more for the reason of reconciling conflicting track standards, as I understand it. Of course the current problem is the business model, and anything that clouds clear outcomes is, in my opinion, to be held at arms length for study. Anyway, I basically agree, at least in the long term.

Charles S Guy said...

I'm sorry but I have to disagree about the feasibility of GRT or group rapid transit.

The point of PRT is small, light vehicles so the track does not have to be made of kryptonite. That stuff's EXPENSIVE!

I like the idea of having multiple uses for the system: passengers, freight, mail, deliveries. This would bring the profit breakeven point down as well. But all these things could be done using the same light, small pods and autonomous delivery drones.

Dan said...

Hi Charles,
Thanks for your comment. I want you to know I would never suggest adding a single gram of kryptonite to a PRT track. Moreover, I would never be in favor of adding any kind of added structure for making PRT track stronger to support heavy GRTs. Earlier in the history of this blog, however, it was pointed out to me that the size of vehicles have less to do with the structural requirements than you might think. This is because the structure must strong enough to support vehicles crowded bumper-to-bumper on the track. As I mentioned in the first sentence of the post, I had originally started the drawing to explore weight distribution, not explore vehicle types. The vertical blue lines represent segments of track capable of each bearing a certain amount of weight. That amount of weight would be the weight of fully loaded, ADA compliant “pods”, bumper-to-bumper. The track, for liability and legal reasons, must be that strong. The GRT pictured would be designed to distribute its load so that it is no heavier on the span than two smaller vehicles. Notice the distribution of the wheels (and their load) is exactly the same as the two vehicles “D”. When I suggest GRT, it would be with that weight limitation in mind. It, would, therefore, be a fairly small for a GRT vehicle, maybe 8-10 people.

I only mention this possibility at all because of concerns I have for the relatively slow boarding of PRT systems being marketed for dense downtown populations. I do so with the recognition that there won’t be a lot of stations in the very beginning of any implementation. If there are only three or four places to go, “door-to-door” isn’t the name of the game. It’s volume. If PRT providers need 25 stations to have a viable density of paying passengers on the track, they’ll be waiting for quite a while, because no city will start with such an ambitious implementation.

cmfseattle said...


either harvard or MIT did a summary of DIA automated baggage and now i can't find it on the web. basically, they were trying to jam the system into tight spaces and bit off way more than they could chew on a tight schedule.

the Flyda hubs-and-spokes: "For example a N bound train can split into a NW train and a NE train and thereafter stations can be half the size and
cost. Further out the trains can split again, until finally the last stations can be little more than bus stops at grade.

public acceptance of cantilevered vehicles would surprise me, although i like the idea of having an evacuation walkway in the center of the guideway.

some engineers involved with the proposed new seattle monorail dissed the system21 outrigger design. i wonder if sensors and ballscrew jacks couldn't be used for active tilting in turns.

cmfseattle said...

according to the ARTA 1989 PRT report, cabintaxi's 12-psgr vehicles were hamburg's idea. they were on the verge of letting contracts when their budget fell apart.

i would think there's a max number of vehicles coupled, which would work with 3-second headways, that would yield a low-cost starter system. in other words, i think it's possible to make a trip GRT or PRT, at-the-station.

suggestion: maybe a BBS format (e.g., vbulletin) would work better, since topics with recent comments would get bumped to the top. i think you can merge redundant threads, too.

Miko said...

To decide what is the correct size or type for a pod misses an important point: we don't have enough data. It will probably work out that different sizes are right for different situations. For example, if a PRT system replaced or augmented the Washington DC Metro, then during rush hour you could probably easily fill a fifteen person car from, say, the Vienna station to Metro Center, and do so in a few minutes. Those larger cars could be put into a depot until they are needed again.

I think allowing different types of vehicles is crucial to the success of PRT. Bengt quite correctly points out that most of the time a system will have excess capacity. Designing the system to accommodate many different needs better utilizes that capacity. For example freight (which I call "the hidden gem of PRT") could be sent though the system at a discount during non-peak hours.

Concerning how to deal with different types of vehicles and how they get into stations, the solution isn't very complex. Any given type of vehicle isn't allowed on the system until it has stations designed to accommodate it. Vehicles for transporting small groups (2-6) would probably be the first step. Then you can have vehicles that accommodate larger groups if the math suggests that would be worthwhile. Freight stations and hospital stations, etc, could be added, often by private funds.