Saturday, September 12, 2009

50> Dualmode and Modular Design

I must say, as measured by email, there is a lot of interest in dual-mode. For those readers not already totally familiar with PRT and it’s many branches and schools of thought, dual-mode is the idea of being able to take a PRT vehicle off of the track and take it other places that the track doesn’t go. Like home or city destinations not served by the system.

I have two problems with this approach. The first is, it seems to me, that a PRT vehicle would make a lousy car, and that a good car would make a lousy PRT vehicle. The second is, that as a business model, dual-mode makes a very difficult transition that much worse. Who wants to buy a vehicle that has no track to run on, and who wants to build track for vehicles that no one owns?

The bad news for dual-mode advocates is that I will not be releasing designs for them anytime soon. The good news is that I will not stand in the way of the future, and, I have to say, I think dual mode will probably happen, once there is sufficient track installed to make it attractive. What I can do for dual mode is to not stand in the way, and to support PRT designs that are dual-mode ready. This happens to be extremely easy to do, because I believe that a modular approach to PRT design would be better anyway.

The above pictures are of a “skateboard” concept chassis from GM, called “AUTOnomy.” Although it is a full 6” (152mm) thick, it is also designed for considerable range and performance. The basic concept is that this platform can be totally driven by joystick. (The pedals and steering wheel would only simulate actual mechanical connections.) Various body styles can be attached as needed.

From the point of view of an open-source PRT standard, the thing to do would be to establish some reserved attachment zones on the bottom of the cab, and have the top “hanger” hardware detachable as well. Ironically, this approach pretty much kills the bottom or top track debate, since the cab would now be capable of attaching to either. This idea is very reminiscent of the MAIT System.

Another thing that came to me while considering modular design was that some of my pet design features are application specific. For example, I have included the ability to travel vertically. The fact is that I seriously doubt that vertical travel would be of much use for PRT, but for industrial and parcel delivery applications this feature might be invaluable. The ability to self-bank around corners would relatively useless for well-packed freight. Clearly the hanger portion therefore should be modular. This is especially true because any suspension would be in this section, and, if ordinary autos are any indication, the perfect ride could take years to perfect, even with smooth track.

Pictured below are some SketchUp drawings of a swing-arm that is removable via sliding dovetail joints. I have not gotten around to the weatherproof power and data connections yet. Actually the pictures are comprised of practice art, as I am just learning SketchUp, (free from Google) so things are not really to scale, or completely thought through.


qt said...

I see dualmode as part of a separate argument. PRT seems to be primarily a thing for built-up areas, whereas dualmode is more for the spaces between. Intercity, for example.

One could possibly see two separate systems in action--something like your PRT system connecting my home with a parking deck/rail line terminal at the edge of town. Call up two podcars (one for the family, one for the luggage), ride out to the station, load up the dualmode van, and go see Grandma and Grandpa out on the farm (or commune or whatever).

Like taking the elevator down to the parking garage to get your car. Except if the PRT system were pervasive enough, I might just rent the car, only when I need it.

So although keeping your PRT system EXTREMELY modular is a good thing, I'm not sure dualmode is really a big part of the argument, anymore than jets are part of the fight over what replaces cars.

cmfseattle said...

when you build on undeveloped property, the first step is to bring in a bulldozer and a dumptruck full of gravel, because that's how emergency vehicles gain access.

dual mode ain't transit.

i suppose that, if you make the transition quick enough (like Jerry Roane's TriTrack), you could simply substitute guideways for highways.

seems like being able to stay in the cabin and leave the skateboard at the park-n-ride would have appeal. one thing i really like about the skateboard approach is that cabin size isn't married to worst-case needs; just rent a larger cabin.

all they need now is a trailerboard version. elvis needs boats

jerry said...

It's hard to know what you're thinking about when using the dualmode term since there are so many different concepts that are being worked on. For example, PugetPullway is a dualmode concept that could use an existing freeway lane in some situations with today's autos and the construction of some overhead mechanical devices. Those who want to review the various concepts should visit and the Dualmode debate page at: dualdbte.htm at the same url. A carefully thought out dualmode concept is the Danish RUF system and it's guideway is relatively simple and it has devised an approach to the "chicken/egg" problem that appears to be pretty feasible. The Bubbles and Beams video from Sweden does a nice job at a cartoon level of explaining what a dualmode system might be like. It's available on YouTube. said...

The "chicken and egg arguement" is way overblown for dual mode. There are several you suggest...of simply having an attachment device on the roof of modified automobiles. The other is to have auto manufacturers produce cars that would be capable of accepting the roof unit once the track is built.
Regular PRT is good for many applications but it can never replace the automobile, because the cost of building the track to every destination is prohibitive. Dual mode on the other hand can reach every destination with reasonable cost. Dual mode has the potential to replace the automobile with something that is cheaper, faster, and more convenient.
Dual mode is a huge hitting a grand slam homer...regular PRT is just a triple.

cmfseattle said...

best post ever

i think detachable dual mode makes things needlessly complex. i'd suggest a design similar to ULTra but which allows privately-owned, compliant vehicles. off-guideway, they'd be NEVs limited to ~30mph. because you don't have taller vehicles like trucks or buses to deal with, a pair of shrouded trolley wires overhead could yield longer range and/or higher speeds.

cmfseattle said...

transportation is broken

Dan said...

Dan the Blogger Makes Comments to the Group-

Sorry for the lack of individual responses, guys. I’m too long winded, have too many emails and am having a hard time keeping this site in it’s allotted time-frame. I wish I could do it full time, but I gotta eat.

Insofar as you are addressing each other and the readers, I really don’t have much to add. I think it is valuable to have these discussions and I encourage everyone to contribute. Insofar as these comments are addressed to me, I would remind all readers to view my posts with the following perspective:

I want to create an open source set of specifications for PRT. Such specifications will, by their nature, fully or partially preclude some existing systems or designs. I am therefore obligated to examine many systems for ideas with merit, and to see if there isn’t some way I can proceed without unnecessarily excluding those designs. I really don’t have a favorite dualmode system, but it seems easy enough to give a cabin both top and bottom-mounting capabilities. This is especially attractive since most existing PRT designs mount from the bottom, and I think compatibility is in everyone’s best interest. If, in the future, someone wants to integrate a detachable cab that can drive away as is, so be it. Everything will be in place. Also, if someone wants to use all or part of the cabin design or components, that is good as well. A lot of this goes back to the track, which must remain as useful as possible, even as first generation vehicles are retired, and as additional capabilities or enhancements to the system are contemplated. (I am still leaning toward a hanging system.) One of those enhancements (and compatibility) issues might be high-speed, for trans-city travel, although I tend to think the sweet spot in the current market is for commuter traffic solutions, since that is where billions are currently being dumped so ineffectively.

Cmfseattle, you seem to be a big fan of ULTra, but not so much Skyweb Express. That is a bit of a head scratcher for me. I personally think ULTra’s big track precludes it from most congested areas. Raytheon’s big track solution was rejected partially on aesthetic grounds, and Vectus hasn’t found a home either. People hate raised highways in the city, (except for the homeless) and fight tooth and nail against them. I can see it for some situations, (Sun City, Campuses, Airports, Zero-emission cities) but for the life of me cannot imagine it solving the traffic problems in Houston, Boston, L.A, Atlanta, etc.
Also “Best post ever?” how so?

cmfseattle said...

Anonymous said...

It's me - the **real** anonymous, with a simple observation.

This dual-mode (tri-mode?) idea is somewhat reminiscent of Cabin-taxi - which could also be used with track above or below - with the added twist of being drivable by the passenger.

I can imagine though that the structure required for the top mount adds complexity & weight to the design. Complexity + weight = expense & increases the number of failure modes, so I would tend to be opposed to such a design.

cmfseattle said...

I think we need to clarify what we're trying to accomplish. What is "congestion"? Really, it's a symptom. It can tell you where a network (roads and highways are a network, too) is being utilized to capacity. In the NY subways, the vehicles themselves are the bottleneck. That kind of transportation isn't for everyone, and you can't paint houses (at least, not very competitively) by subway.

My next questions are, Can PRT guideways be built using PRT vehicles? Can we build neighborhoods using PRT vehicles on PRT guideways? At what point does PRT begin to affect land use patterns? When you go shopping for a big-screen, would the store lend you a freight PRT vehicle, so you could dispatch it to your garage on your restricted-access PRT siding?

So Dan, to answer your question, I'll say that I currently favor ULTra. The concept needs operational experience. At this point, we need something that looks enough like a car/dualmode/PRT to gain momentum.

Freeway volume on PRT

John Greenwood said...

The public acceptability of PRT is a thorny issue. I have tried make a comparison of the different types of guideway.

My conclusions are that the best configuration is neither suspended nor supported but one where the guideway strangth members are either side of the vehicle.

Overhead systems are going to be intrusive and the differences in visual intrusivness are marginal.

What about putting the track underground in the most sensitve ares? We need a guideway design that is elegant both overhead and underground and is both elegant and much cheaper at grade.

I also suggest that in the longer term stations at grade will be essential and this will require verticle movements from from both underground and overhead guideways.

Dan, I am enjoying this blog but I wonder if your ingenuity and that of your readers would be better directed towards these unexplored territories?

Stuart H. said...

This post is regarding dualmode top-supported vs bottom-supported. I am interested to hear a good argument for top-supported dualmode, because I just can’t see it. Also, I assume dualmode because I do not see non-dualmode PRT ever getting off the ground. However, I isolate the support style topic here because there are so many aspects to consider in general that there needs to be focus.

My argument for bottom-support:
I don’t like the “hangers” on the top-supported systems.
Hangers can be part of the vehicle or part of the guideway. As part of the vehicle, the hanger either increases the height of the vehicle if it is fixed, or adds unnecessary weight and complexity if it is retractable. As part of the guideway, the hanger takes up physical guideway space and continues to be a burden on the traffic-processor computers even when it is unoccupied. If the hanger stays on the guideway now has moving parts which adds a cost and maintenance burden to the entire system. Hangers, in general, also present other problems. There is the problem of adapting to the vehicle height at the entry/exit stations. Also there is no way to drive the hanger off of a guideway that has lost power without adding an extra drive unit to the hanger itself.

A bottom-supported system does away with hangers and their problems. The pallet portion of the vehicle always leaves the guideway with the vehicle, thus relieving guideway congestion and processor burden. (I consider stand-alone pallets for pre-dualmode vehicles as vehicles themselves.) Because of this, a bottom-support style guideway would have no moving parts. The entry/exit stations would not care about the vehicle height of bottom-supported vehicles. They would all attach the same. A bottom-support vehicle could also conceivably "drive" off of a guideway with the wheels it already has in the event of guideway power loss without need of additional equipment.

In fairness, the guideway of a top-support system would probably be less prone to weather obstructions and might be less costly per mile. It is more futuristic looking too. But for overall practicality, I remain behind the bottom-supported style.


Andrew F said...

Stuart, it is interesting that you think dual mode is the only viable form of PRT, given that all the commercially deployed PRT systems are pure PRT. ULTra is being rolled out fairly aggressively with two likely concessions being granted in India.

Dan said...

Dan the Blogger Responds… (I’m coming back to civilization soon, I promise!) Hi Stuart, thanks for your comment. I second Andrew’s observation. Stand-alone PRT is a business model that presumably will pay for itself with fares or undercut the costs of free shuttles. It’s moving forward on that basis, while dual mode’s business model is far more murky.

It seems to me that you are looking at the problem from a vehicle-centric standpoint. The problem is more with 2D transportation and lack of space for it. There is little point in making a PRT system for your family car. That is essentially just making more roads. The money could be better spent on conventional street improvements, and then there’s the whole “chicken-and-the-egg” problem if the vehicles are modified. Which comes first? The modified vehicle or the track? The computer-in-the-sky traffic management, the self-navigating, even self-driving technologies are already here. So just skip the PRT part. Or on the other hand, if you want to move tons of people around a city really efficiently, make an infrastructure that is scaled specifically for transporting human-sized payloads in full 3D. And make it a system that won’t have ramps and ground level tracks and all of the other things that home owners and business people along a proposed route would object to. Have you ever seen how fast people mobilize to stop a road widening or light rail project in their front yards? Suspended PRT is admittedly not optimized to move personal vehicles around. (I assume that’s what you mean by dual mode because you remark about hangers not being adaptable to different size vehicles) So if that is your object, I agree with you. From that perspective, bottom supported is better. But as I have stated many times, PRT and automobiles don’t really mix. The things that make a great car (good suspension, tires and steering for example) just add weight that is multiplied all along the track making the whole system bigger, uglier, and more expensive. BTW, one advantage to PRT is the ability to use electric power from the grid. With an overhead track, the electric lines are kept safely out of the way.