Sunday, December 27, 2009

65> The Efficiency of Absence and Angled Wheels

Before everyone’s eyes glaze over from too much shoptalk, I would like to ask for nominations for the best videos to explain PRT to a complete newbie. It is time for me to update my “About This Blog” sidebar, and I want people who stumble on this site to go away believers without me having to waste a lot of space trying to explain it.

Speaking of the sidebar, I see my “Recent Comments” list is still blank - at least on my computer. If anyone is getting the list, or knows how to fix this widget, let me know. It would really help keep threads alive.

As most of you know, I am trying to finalize the design of the most cost effective, versatile PRT track design for suspended systems. Unfortunately, this entails exploring every conceivable use, limitation and bogie design. Higher speed. Tighter turns. Steeper slopes. Industrial. Freight. Heavier loads. Cheaper Stations. Manufacturability. Longer Spans… “Pod” designs may evolve, but the track stays, so we need to get this right. I have taken the approach that the running and guidance surface dimensions are a somewhat separate issue from the structural truss, and that these surfaces can basically be surrounded by a support structure. Inside, for example, most structure is no longer needed, because the running surfaces can be supported (hung) at frequent intervals. Anyway, it mostly comes down to the bogie design.

I have, lately, been working on a problem inherent to rail based PRT designs - the shear number of wheels required per bogie. Here I show an older bogie design with 18 wheels.


True, half of them need to fully disengage to switch tracks, but still 9 per side seems like a lot. In post 54 I show a much simpler configuration, with railroad style flanged wheels and little guide wheels that fit between the two halves, but this design is unworkable for high speeds. Post 56 shows a high speed-bogie, but with no steering wheels, so do not be confused. As you can see from the picture below, PRT’s acrobatic unpowered cousin, the roller coaster, requires many wheels as well, and would require still more if designed to switch tracks via steering guide wheels. 

In railroads, they cut the number of wheels from 16 to eight by adding a flange to each wheel. The problem is that the flange creates friction with the track which would tend to overheat and wear it out at high speeds, smaller wheel diameters, or if it were made of some material other than conductive, strong (but loud) steel. To minimize wear, the designer must keep the wheels perpendicular to the rail surface, hence the 24 wheels per roller coaster car.


Some years ago, while arguing over a design detail of a piece of factory equipment I was designing with a machinist friend, I came up with this axiom. “There is nothing more efficient than absence!” I have returned to that thought many times since. So how can I get some of these darn wheels to be absent? Without flanging the wheels or track?  While steering guide wheels can be disengaged for straight runs, guide wheels for centering the bogie cannot. One thought is to wedge the bogie in the track with angled wheels. Here is what I drew to help me think.




Could this line of thinking mean I need to take my track design completely back to the square one, after all of these months of exploration? The verdict is still out, and I have some more mature designs to share at a later date, which require some fairly lengthy explanation. But it is Sunday, and I’m in the middle of remodeling my bathroom, so I will bid you all a Happy New Year.  




Sunday, December 20, 2009

64> The ULTra Architecture - Continued



In the last post I touched on the idea that vehicles such as ULTra could be driven by “joystick”. This idea of driving by electronic controls (as opposed to the current practice of having actual mechanical connections between the pedals, steering wheel and the engine and brakes,) is not new. The use of electrical motors and regenerative brakes starts us down that road, which leads to the “skateboard concept.” (scroll down to post 50 for a picture)

Let’s take this line of thinking a step further. If the Ultra vehicles are guided by some kind of laser system that centers them on the track (with accuracy of less than a centimeter, I understand) such a system could presumably be fitted on private, steerable cars as well. An example of a steerable car which could presumably be easily modified for the ULTra control system is this Michelin concept car. The idea is that you drive your car to a ramp (or car “elevator”) and driver control is switched off and automatic control is switched on. Voila! You are now in a fully automatic PRT system until you are dropped off.

That Michelin video raises an important point however. People are really in love with their cars. The very best selling point of this electric car seems to be its muscle. Then there is the addition of luxurious creature comforts, such as adjustable seats, high-end music, etc. It seems to me that private vehicles will always become more and more loaded with features and power until something or someone steps in to halt it. Electric vehicles, in themselves, are not without environmental costs. The electricity they use must be generated, and this, itself, generally involves combustion. The prospect of hundreds of millions of Chinese cars being recharged by way of coal (their principle source of energy) power plants is truly frightening. Coal is, of course, 100% carbon, so there is no fuel on earth that is worse for global warming. Anyway, the point is that there would need to be some kind of societal decision as to how much to limit the power and weight (and therefore luxury) of these vehicles. We can’t afford a guideway network for Hummers. Because any vehicle on the system would need to be meticulously maintained, (combined with the necessary luxury limitations noted above) perhaps some type of leasing model would be the way to go.

This scenario does not eliminate “ordinary” PRT operations. Fully automatic “taxis” could still populate the track. PRT vehicles could come down to ground level and use a special lane to get to stops which cannot be served by raised stations. This would, of course, create the same interferences with vehicular and pedestrian traffic that plague other forms of surface transportation.

The main problem with the whole idea is the same problem that plagues all supported PRT systems. All supported systems inherently discourage true point-to-point travel compared to hanging systems. If they come to the ground they interfere with other traffic and pedestrians. Ramps must be fenced off for safety and are ugly. Stations must be positioned so that ramps won’t block driveways. If elevators are used to raise the passengers or lower the vehicle, the station is considerably more expensive. This is a big deal if you consider the economics of the network. I believe that in many cities the ridership figures are such that a great percentage, maybe even most, of the city would go unserved by the PRT network unless simple “bus-stop” type boarding areas are employed. I think this is a point worth repeating. It is a very big problem if the cost of stations precludes their use in large areas of a city. PRT needs the “network effect” to fulfill its promise as a transformational technology. Of course this is just money problem. If the government wanted to switch some road funds into PRT that would be a different matter. From a business perspective though, there will always be a number of riders under which it becomes unprofitable to create local service.
For the time being I remain very wary of any system that can only take the “low hanging fruit” to market.
Merry Christmas!

Sunday, December 13, 2009

63> ULTra – Architecture and Iteration


There has previously been, in my mind at least, some question about whether ULTra is really PRT. After all, the 40 km (25mph) speed is hardly “rapid”. And the distances that passengers will be willing to travel at those speeds are somewhat limited as well, although I suppose they are far enough to be legitimately called “transit”.

I started writing this post with a number of negative suppositions. I have previously criticized the ULTra design for being little more than a golf cart, and wondered aloud what the advantage of automating such a vehicle really was. Actually I was about to call for ATS (The company that makes ULTra) to consider a purchase of company like Taxi 2000, or PRT International, as a way forward out of the constraints of it’s present design limitations. I am forced, however, to reconsider.

I have been selling the ULTra designers short, I now believe, and this is why.  Many of the aspects I don’t like about ULTra are truly intermediary. They will not stop ULTra from becoming much better (and more versatile) in future iterations. It seems that the designers over at ITS have a motto of extreme simplicity and conservatism. Anything else is kept “close to the vest”.   Here is one example. The traditional steering, (as opposed to track constrained steering) at first glance, would seem to have all of the negatives of cars. It would skid on ice, for example. Safety issues would seem to prohibit any kind of speed with an automated guidance system. The idea of a track would seem SO much better than trying to center the vehicle with lasers and sensors. So why didn’t they do it? Well for one thing, tracks are less versatile, because they prohibit the vehicle from being able to move freely on any paved surface. But it is mostly, I believe, because they didn’t need to. Tracks would offer the potential of much higher speed but they don’t need speed. It’s only an airport “people-mover”. But the fact is that a track or guide rail is still perfectly compatible with ULTra. They just chose not to use one, for now. Lasers can be turned off, but you can’t easily pull up the tracks. Therefore lasers win. If and when speed becomes an issue a simple rail that sticks up under the center of the vehicle could be added, with minimal modifications to the vehicle.

One interesting aspect of ULTra is that it could presumably be driven away by a human operator, using a plug-in video game style controller. This would seem like a natural way for mechanics to move vehicles around a maintenance facility, for example. That raises intriguing questions about dual-mode, doesn’t it?

Don’t be too put off by the weight. They are using the old, heavy, lead-acid batteries. But once again, the only trade-off has been to design-in some extra space. They can upgrade to Lithium-Ion or even third rail at any time. It was explained to me that track electrification was deemed too costly, but I can’t help but wonder about partial electrification, so that the batteries could get some on-route charging. The possibility of easily swappable batteries also comes to mind.

I also hate the track, especially as seen from below. That would seem to be a hard sell for city streets.  This, also, is not really an issue that can’t be much improved. There is nothing that says that the track must be massive concrete, for example, although noise could become an issue of the track was pure steel. There is a gradation between rails and roads. If redundant road area (anything not in line with being directly under the wheels) is removed you are left with a pair of very narrow beams – seems pretty much like a pair of rails to me. ULTra can theoretically drive on such “rails”.

I guess the lesson here is to beware of false choices. This does not just apply to Ultra. I was bemoaning the huge turning radius of the Anderson designs and a similar thought occurred to me. There is nothing inherent in the concept that prohibits tight turns. It I just that it necessitates a more complex bogie than is called for in the current business plan. 

It is easy to look at a system from afar and the hard choices that have been made and to rap them up as defining that system, rather than see them as a collection of business decisions. ULTra is not a clunky, slow, heavy vehicle on an ugly, massive roadway. ULTra, like other systems, is an architecture first, and the rest of it is a means to salable iteration of that vision. This architecture, I am finding, is surprisingly tweekable.

Sunday, December 6, 2009

62 > Mission and Miscellanea



First on the agenda, readers may note that our “Recent Comments” feature has disappeared. It was rather peculiar. I was on the phone with someone asking if it was just my machine, which it was, and then he refreshed his screen and it was gone for him too. It turns out that it’s a third party “widget” and I have left a cry for help on their site. We’ll see what happens.

I have recently included an index under the search box. It is very incomplete at this point. It is actually a link to post number 0, so if you find I have a glaring omission you can say so in the “comments.” I will try to periodically delete these comments as I address the issues to which they refer.

I want to clarify something. I have shown a lot of different designs since this site started and one might be tempted to think I am just throwing them out there, to see what sticks, or that every design cancels the one before it. One might think that I am inventing and improving “my system.” This is not exactly true. Actually what I have been doing is trying to verify a “best” suspended track design and finalize its dimensions. My reasoning is that while a PRT provider could go out of business and vehicles may come and go, wear out or be improved piece-by-piece, the track will stay until someone tears it down. We cannot know what technologies or configurations will be desirable or employable in, say, 30 years. (Or how the city’s transportation needs might change) We can, however, create a design that is as flexible as possible. This flexibility can include the ability to accommodate different neighborhood types, vehicle weight classes, speeds, special purpose vehicles, propulsion types, and station types, turning radii and slopes, while being easy to construct, deconstruct, and connect to.

I do not think it is altogether coincidental that the two active PRT platforms run on a road-like surface, which can be used for other vehicles if the projects or companies fail. It is simply insurance for the buyer.

Therefore one of my aims is to provide a track profile that is not entirely incompatible with the various PRT technologies available. I would like to see a track that could be readily adapted by one or more PRT venders, so that the track expense does not represent a total financial and political risk. In this respect I diverge from most would-be providers, who require absolute faith in both their proprietary products and their companies. (Most of which are not scaled for any actual contract) I hate to say it, but this seems extremely naive. Is it any wonder that their proposals don’t carry much currency with those entrusted with the public’s money? We, in America at least, have seen many of our pillars of industry and finance file for bankruptcy in the last couple of years. Do these “companies” actually think that they can scale up to manufacture vehicles, lay track, and manage an untried network all at once? More importantly, do they think they can sell that scenario? There’s a clock named after this kind of optimism.

My approach, again, (43% of this site’s readers sample as new, so I repeat myself with purpose) is this. Standardize the basics. Document consensus. Establish common ground.

Where do the companies promoting bottom-supported PRT fit in with all of this? It is my intention to eventually examine these systems as well, with an eye toward addressing any major shortfalls constructively. (Readers will note that in Post 48 I suggested a way to double the throughput of a small-footprint elevated station for almost no additional expense, for example).

A common pitfall in design stems from starting with a set of assumptions and continuing from there. The more you invest in those initial design assumptions, the less likely you are to consider that, perhaps, you were wrong in the first place. I have invested a good deal of time exploring suspended systems, and almost none with the supported designs. Perhaps my original objections can be easily addressed. How can one tell without actually going back to square one?

Finally, there are a couple of obvious flaws in the classification system I suggested last week. One is the use of the letter “x” for both spacers and to mean “Does not apply.” A minus sign would be seem to be a good alternative. Also, (as pointed out by an alert reader) the term “articulation” is not self-explanatory. It does indeed refer to tilting the cabin with respect to the track to adjust for slopes and curves. Pitch and Roll are aviation terms. In the system I did not allow space for both Pitch AND Roll articulation. This, as you can see, is a work in progress.

Saturday, November 28, 2009

61> Classification of PRT/PAT





One of the essential steps in any kind of open-source collaboration would be some kind of classification shorthand to enable the parties to better reference their work, and the work of others. For example, if I want, presently, to refer to a system in which the vehicle is perched on a vertical extension of a captive bogey which extends from a slotted track, I have call it an “ITNS” or “Ed Anderson” design and mention Taxi 2000” or “SkyWeb Express”, (or vice versa) to be evenhanded. Making comparisons and design offshoots using those and a few other systems in a single discussion could get pretty confusing. The confusion would extend to procurement, contract awarding, etc. At some distant future point, someone will create some kind of certification process for aspects like track construction. That’s kind of hard when you can only describe the track in terms like, “It’s like the ULTra track but it will have screened middle sections like MegaRail…with a third rail…”

Originally I was going to fold this all under the “SMARTS” umbrella, (Small-scale Modularized Automated Rail Transit System) but realized that some important systems fall outside of that description. (A little note here. I think I like “Standardized Modular Automated Rail Transit” better. It is more descriptive of what I am up to…) Anyway, I believe breaking up the systems by key attributes, rather than vendors and inventors, allows a more substantive dialogue.

There are also obvious disadvantages. First of all, without the above picture as a key, nobody can use the system to classify anything. Secondly, who really knows the exact numbers to put in for the various systems except the designers themselves? I imagine one half-solution would be to simply “x” out the unknown latter details, so that the ULTra would be a “BGBxx” while MISTER would be a TIxx and I have been designing a TELxx, but Anderson likes the BELxx.

All I can say is that just because I don’t have the resources to make something happen, it doesn’t mean it is entirely useless to point the way. After all, classifications are essential for everything else, including roads, bridges and the vehicles on them.

Finally, I would like to thank alert reader “afransen” for pointing out that I can feature recently posted comments on the main page. (On right, scroll way down) This may help stop threads from going dead so quickly. Unfortunately it doesn’t show which post the comment refers to. Perhaps very alert readers will learn to preface their comments with a post number when they are commenting on older threads, which I will do myself. We’ll see how it goes. I’d love to see the threads get more content rich over time.

This feature is one of what Google calls “Gadgets” and it turns out that there are a whole lot of them, including the our new search feature. Believe it or not, I have been spending time every day this week creating an index. If I had known about the search “gadget” I would not have bothered. Now that it’s half done, I will probably finish it. If anyone cares, it is post zero. (oldest of the old posts) It links to posts by subject matter. When it is more complete I will show it as a link under the search bar.

Friday, November 20, 2009

60> Prestressed Concrete Track for PRT and Other Automated Transit



One concept worth considering is making track from prestressed concrete. I’m not sure how it would work for the inner city or spans with a lot of curves or branches, but it might be a good candidate for freeway medians.



The groove on top and the corresponding hole in the support structure is for electrical or communication cables, and is meant to be covered by a metal cap. One might be tempted to question whether it is really feasible to cast such a shape. Actually it is really excellent, because by piping steam through a collapsible inner form, the concrete can be caused to set much more quickly. Beams can, in this manner, be removable within hours, allowing multiple castings per day.



The picture above shows the various rubber-mounted running surfaces associated with the previously shown designs. In a situation such as a high-speed longer distance application, not only would the rubber be unneeded, (concrete absorbs sound which, in freeway median applications, wouldn’t be and issue anyway) but most of the steel itself could be dispensed with, as well.
In applications with lots of stations and curves and branches it is easy to imagine a track in terms of a profile that serves all of those needs. For the duration of long, straight runs, however, the metal “fins” used in switching need not be present. Furthermore, larger wheels are probably in order for higher speeds, as suggested in post 56. Therefore the running surfaces normally used for the smaller low speed guide wheels should be removed or recessed, so that the small guide wheels don’t spin. In fact, I’m not sure that any of the steel shown is needed.
Without any buried utilities to prevent more closely spaced support posts, this might be a very cost effective way to handle the commuter market and reduce freeway traffic.

By the way, it occurs to me that most readers, even those with some engineering instincts, would be intimidated by the thought of trying to learn a new program, especially a 3D modeling program. Well the folks at Google are no fools, and they wouldn’t get into the 3D software business if they didn’t have something pretty special.

Here is a chair that I drew in under 3 minutes, following this YouTube tutorial. Try it. It’s fun!






Saturday, November 14, 2009

59> A Milestone and a Call to Arms

Many of you who have followed this site, which is now nearly eighteen months old, may be wondering about this “Open-Source” thing. Obviously just showing my own design ideas isn’t really open-source. At the same time, I started at a readership of zero. I had to achieve some visibility. There has always been a compromise between what would grow the site and what would populate it with engineers. Anyway I have decided that it is time to take this project to the next level.

For several months now, this site has had the capability of enabling not just the sharing of my designs and ideas but of yours as well. Unfortunately, I’ve had a lot of problems figuring out what I was doing so I could clearly explain it to you, the readers and potential users. The problem was compounded because it really takes more than one computer and IP address to experiment with a system like this. Luckily I have recently found the time to at least partially figure it out, so, without further delay…HERE IT IS! (Corks pop and the sounds of noisemakers ensue)

First, if you want to not just look at my designs but play with them like you had drawn them yourself, I have posted the address of a download site to the right. (You will currently need Google’s free 3D modeling program “SketchUp”, although later the site may be populated with many other file types.)

Furthermore, they may be improved and resubmitted, or you can share your own projects. PRT control software would be nice!

It works like this. Google holds the files. We each have folders, which, when updated from the Google site, will have identical contents. Each of us can then open any project file in the folder and work on it. When we want to quit, we simply close the file in the usual way. It can then be either submitted to be shared, or reverted. If it is submitted, a text box will open where you will hopefully describe your work, so the rest of us do not get confused. You can also share your own project files by putting them in the folder and submitting them. Another option is to branch a project by changing a file and submitting it under a new name.

This is all done by a magic little helper program. (SVN) I am using one called Tortoise.
It runs in the background and you access it by right-clicking the file or folder to get at its menus. It places little badges on the file icons in your folder – blue for one you just added, red for one you just modified, and green for the shared version that Google is holding. (A note on SVN jargon - Submitting a file is called “committing”. Your folder is called a “local repository”.)
So anyway, by right clicking, you can ADD, REVERT, COMMIT, (individual files) or UPDATE. (The folder)

To get started, just go to the OpenPRT site, and go to “downloads” to get a MS Word doc with step-by-step instructions. By the way, those files under “Downloads” are already old. It’s best to go to “Source” > browse> svn>trunk to get the whole up-to-date library. Right now all I have is mostly the models that I used for illustrations for this blog. At some point we will need to start designing in earnest, from scratch. Note that there is even a wiki. This might just become the most important part of the site because wikis are great at linking related subjects. The design of any part of a PRT system inherently relates to many other parts, as well as to statements of design requirements, such as safety, cost, modularity, replacement/repair cycles, etc. With a wiki, every part can have it’s own page, and everyone can contribute and edit. This part-by-part discussion can then be put into 3D and worked on via the SVN. At the present the wiki is like a big unopened box. I invite you to create the first page.

It has become clear to me over the past months that I will need a lot of help with all of this. I think it is worth starting discussions about how to incorporate volunteers and create some kind of formal administrative structure. Wikis, SVN, managing open source projects…. None of this is really up my alley. I really hope we can get some good discussions going in the comment section this time. I really could use some guidance as to how to make this thing unfold.

Saturday, November 7, 2009

58 > Defining The Problem

One of the hallmarks of PRT/PAT travel is that the vehicle takes you from your origin directly to your destination with minimal waiting time. There are no transfers, no stops for other passengers, etc. The track, being for small vehicles, can be so light and inexpensive that it can be built into very extensive networks very cheaply.

In practice, however, the initial track layout will be extremely limited and it will take many years to spread citywide. Therefore it probably won’t take you from origin to destination. Furthermore to really make an impact, PRT should address the commuter, not just travel around the central business district. What is the point of PRT if you need to drive 10 miles and pay for parking to get to it? Do the models that various PRT venders are promoting address the crowded freeways? Is any PRT model that addresses the freeways even close to the model that addresses the central business district? What about the suburbs?

If the need were only in the Central Business District (CBD), I think I would give the edge to the general design parameters envisioned by ITNS/Skyway Express models. This will surprise many, as I have a record of advocating a hanging system. The difference is, in the CBD, the main emphasis is footprint. Speed, and cost of track and stations are secondary. Having elevators in every station is actually a pretty good way to economize sidewalk space, and it takes less energy to lift a passenger than a whole vehicle. In an environment of all multi-story buildings, second floor stations can be accomplished with little more than a balcony.

The situation changes markedly as the system expands outward from downtown, however. Here, the expense of the track and stations becomes critical as individual station ridership begins to drop. In these areas, bus rides to town are short and convenient. Putting up elevator-equipped stations on every block is far less attractive than it was downtown. Now the advantage, in my opinion, shifts to hanging systems, because they are generally more versatile in terms of slopes and curves and multiple speeds, and can accommodate open-air stations that may double as bus stops. Because of population density, stations should still be within walking distance of each other, but many passengers will just be passing through.

Next comes the suburban sprawl. This mixed-use area goes on for miles and is punctuated by mini urban centers, residential neighborhoods and distribution parks. There is enough housing and employment that many of the residents never go downtown. Here distance, and therefore speed, starts to become a real issue. The potential riders currently utilize a variety of road types to get around. Often there is a freeway nearby. The challenge for the PRT planner is to provide a system that can match speed and convenience with the combinations of freeway and back street shortcuts that are utilized by the drivers living and working here.


Because of the sheer size of the suburban sprawl, it is unlikely that any form of PRT will blanket such an area for quite some time. This suggests a “low hanging fruit” strategy, where major “hub” areas are accessible but many low volume routes are not incorporated at first. City buses (horrendously inefficient for long trips because of the many stops) could, none-the-less, be a reasonable option for going a few blocks to get on the PRT grid. Here it would seem to make sense to have some kind of PRT express lanes that go quite fast to connect community hubs. This is an entirely different model than the CBD, both in terms of preferred track and stations and preferred vehicle. Speed, versatility and track cost would seem to be the main design factors.

Finally there are the outlying suburbs and satellite communities. Commuters typically travel at posted speeds until they get close to town and then traffic backs up. These people generally have large engine vehicles because aggressive driving, for them, is somewhat of a survival skill. Keeping these cars out of city limits would do a city a lot of good. Here 30 mph PRT would be useless. It must be much faster to compete with the freeway. People in outlying communities cannot expect to have PRT vehicles come by their homes. Dual mode vehicles would be a poor substitute for the pick-up trucks and SUVs that get them around now. To be perfectly honest, I have serious doubts about whether PRT is the right tool for this job. It certainly calls for fast vehicles on a fast track, but why individualized vehicles? A park-and-ride GRT (Group Rapid Transit) station on the out-of-town side and an ad hoc drop off scheme might be a more efficient. Here is some thinking on this.

The main drawbacks with group travel are waiting and having the station locations that are catered to the average passenger but are not anyone’s exact origin or destination. I believe, however, that with automation and an intelligent system these problems can be largely solved. For example, the problem of fixed scheduling and associated waiting is largely a communication problem, as is inconvenient transfer locations. (Passengers and transit have had to meet at a prearranged time and place, because it is presumed that they can’t talk to each other.) If the “system” knows the complete itinerary of every passenger, the right size vehicle can be sent at just the right time for the group. Is transferring a really the problem if the time waiting for the transfer vehicle is eliminated? After all, PRT vehicles can swarm incoming GRT vehicles moments before arrival, and the “system” can decide where this meeting would take place. GRT requires heavier track, but the other choice may be requiring all PRT vehicles to be more costly and robustly configured than would otherwise be the case. Building super fast PRTs to go slow is a waste. Building high-speed high-capacity track might be a better investment. After all, this might find dual use for freight. There is also the matter of spreading the weight. Perhaps a “fast lane” with greater headways between vehicles and greater spacing between bogies would not need to be that much more expensive.

The track profile I have been working on is specifically designed to be adaptable for multiple weights and speeds. This brings up the question of track “permissions.” Obviously a heavy vehicle must not use light track, but light vehicles could use heavy track. Clearly slow vehicles should not hold up fast ones, but fast ones might want to use a slow track, on occasion. These questions are for a different day, but, to rap it up, I suspect automated transit is not a “one-size-fits-all” technology, and different parts of a city have differing transit needs, and therefore different optimal designs. I also wonder… What starting configuration gives the most bang for the buck?

Next week: The long awaited grand opening of the design collaboration site.



Sunday, November 1, 2009

57> Roads, Roads and more Roads

A note about this post… One of the problems with a blog format is that the passage of time buries old posts more and more deeply, and with them, ideas that were considered foundational. After 57 posts, how do new readers even know what I’m talking about? I am caught between trying to build on previously explored concepts and not becoming so obscure as to turn new readers away. What follows is not exactly new to some of you, but will be to many. I think it is important to try to get everyone on the same page.

PRT has been aptly described as “The Physical Internet.” (Bill James, JPods) But what really fits the bill is the present road system. They don’t call the Internet the “information super highway” for nothing. Our road system has become an amazingly pervasive network, and, coupled with cheap fossil fuel and advances in cars and highways alike, has created the most mobile population that the world has ever known. The system works so well that very few people ever consider the negative implications of continuing its expansion. Also invisible, to most of us, is its costs. In fact, the only thing that wakes us up at all is when the system breaks down.

Roads have been built on tradition, more than real analysis of transportation design requirements. Paths became trails, carts needed flatter wider trails, faster wagons needed smoother roads, then there were cars, then trucks. Now our little paths need to support 80,000 lb. vehicles and can be hundreds of feet across.

It’s not that roads are cheap. They are not cheap to plan, to fix, to clean, to patrol, to connect to, drain around, to elevate, to bank, to clear from accidents, grade for, purchase land for, license drivers for… I could go on… But the costs are so buried in established practices that we don’t even see them anymore. We can’t even imagine a world without that money leaving our collective wallets. We not only lose millions of hours each day in traffic, we perversely pay more for roads when we are stuck in gridlock, through taxes levied on the gas we are wasting. (A little footnote here: As cars become more fuel efficient, these funds for road improvements decrease. Eventually the cost savings from owning a more efficient car will need to be offset by higher taxes.)

We can’t do without a sophisticated transportation network. That Genie cannot be put back in the bottle. But the developing world (and the world at large) cannot afford to see this concrete network model unfold to its logical conclusion.

Suppose we could start all over again, but with modern technology and environmental awareness. Knowing what we know now, were we dropped onto a primeval planet, and had to build a new network from scratch, would we begin by terraforming the habitat with bulldozers and dynamite so that foot thick ribbons of concrete could connect parking lots with each other, as the preferred way to connect structures, goods and people? Wouldn’t it be cheaper both in the short term and long term to plant some pylons in the ground to support pre-fabbed sections of guideway or track? (Don’t forget the environmental impact of changing drainage patterns and the habitat segmentation that roads create.)

I acknowledge importance of truck access. It’s pretty hard to build a house without it, much less a building. Yet truck access also shapes need and development. First comes truck access, then comes deforestation. Soon to follow are deliveries of heavy, bulky materials that can only be delivered by, of course, truck. The economics of suburban sprawl are directly tied to the economics of our “physical internet”. I do not pretend that this hypothetical alternative transportation network would be equal or advantageous in all respects. We have become used to having virtually all addresses accessible by very heavy equipment, even hundreds of miles from city centers. Would the pioneer inhabitants of our brave new world choose to abandon the road paradigm altogether? I doubt it, but I can’t imagine that they would want to revisit all of the cost and effort and environmental damage that went into the present system either, were a viable alternative available. I think they would look at the road for what it is, a great way to deliver truly heavy freight beyond shipyards and train yards, but not such a great medium for a one-and-only, all pervasive “physical internet”.

So what would make a great “physical internet” in this brave new world? Four things.
1. Very cheap. (in materials, construction costs, and upkeep)
2. Very versatile (as many applications as possible within the constrains of it’s form)
3. Elevated, both to unlock the value of the land below. (economic, aesthetic, environmental) and to minimize the amount construction that needs to be done on-site.
4. Very, very efficient, meaning fast, low energy, high though-put.

There are many iterations of PRT/PAT, but the two projects currently under construction, (ATS’ Heathrow Airport and 2getthere’s Masdar City ) projects are based on the familiar concept of the road, although it is usually described as a “guideway”. I hope these companies have a firm grasp on just how poorly their "guideways" stack up, on the basis of the above-mentioned criteria, compared to other designs that have been put forth. With any luck they already have “second generation” plans in the works. At the moment one is forced to compare their systems’ performances to that of user-driven electric vehicles on a similar guideway. I acknowledge that “going electric” and reducing lane widths is a major improvement. But why not just widen bicycle paths or paint off sections of road for small electric vehicles, private and/or rented? What is the point of having vehicles do something automatically that people can do as well or better? The value of automation comes when machines can vastly out-perform their human counterparts. It would seem that weather, or pedestrians, for example, would tend to keep automated roadway based transport forever slow for safety reasons.

Every journey begins with a single step, and the people who control the money are rightly conservative, and roads are familiar and proven, so I heartily endorse these projects, and congratulate the companies for landing the contracts. The driverless automation part, though less than essential on roads, is an absolute requirement for raised thin-guideway or rail systems that need sophisticated traffic management. All PRT efforts help develop that key element, so these companies are providing a needed boost. But let’s also keep our eyes on a bigger prize – a next-generation “physical internet” that is vastly better than what we have now. Only a system that demonstrates overwhelming superiority (by the previously mentioned criteria) will have the ability, in a free market world, to significantly impact our longstanding transportation traditions within our lifetimes, and so deliver the benefits that such a system could bring to all of humanity.

Sunday, October 25, 2009

56> HIGH SPEED

This week I’m going to switch from low speed industrial and delivery to high-speed intercity travel. After all, once you modularize a PRT/PAT system, it opens up a lot of possibilities.



Here we have a high-speed tractor bogie, meant to act as an “engine” in the “railroad” sense of the word. By hooking one of these to a PRT bogie, (all done inside the shelter of the track) the PRT vehicle gets a big infusion of horsepower. This is directly analogous to adding engines to train cars, except in PRT the “cars” only need the engine for very high speeds. The cone part is an electromagnetic coupler with a data port in it. It uses the self-aligning qualities of a Morse taper, with magnetism and a limited travel universal joint to allow coupling and uncoupling via magnetic pole reversal. The pairs of enlarged guide wheels pivot to create a self-centering mechanism for the bogie. They are enlarged to retard the wear on both tire surface and wheel bearings that would come from high speeds and long distance travel. There are no provisions for steering shown, although they probably need them, to travel independently when needed. I would think that all small guide and steering wheels should be disengaged for high-speed travel though, because it would just wear them out for nothing. This idea would support the concept of removable, rubber mounted, guide-wheel running surfaces inside of the (municipal) track. (There are a number of other benefits to this idea) For high-speed sections these would just not be installed, leaving the smaller wheels with nothing to keep them spinning. Provisions would be required to get them up to speed before full reengagement, however.



The picture above shows how such “engines” could be used for high-speed intercity travel. Whereas the first pictures only showed the part that resides inside of the track, this picture shows an aerodynamic drag reducing “shell” that hangs down. (in blue and gray). As vehicles reach the end of the municipal track, “engines” fall in behind each of them until the system decides on a logical end point to the train. This “ad-hoc” monorail train can now travel at speeds that would be impossible for the PRT vehicles alone. Upon reaching the destination city, the train breaks apart, the PRT vehicles continue to their respective destinations, and the engines make a big U-turn and line up for a return trip. Such a scheme could (and, eventually, probably should) employ Meglev, (once public funds are as available for track as they are for roads) and I would shy away from any design commitments that unnecessarily preclude this eventuality.

Lastly, note that I have numbered my posts. Eventually I will include an index, since the vast majority of readers have found this site relatively recently.

Saturday, October 17, 2009

55> Chasing Trucks


I found myself following a beer delivery truck the other day, and when they pulled into a parking lot, my reporter’s instincts kicked in. My suspicions proved well founded. First I asked the driver (who had a helper) about the usual route. It turns out they had been on the road for 8 hours, since 6 AM. It was 2 PM, and they weren’t done yet. They told me that they intended to deliver for another couple of hours, and worked partially on commission. I asked them where they were working from and they indicated that they were about 20 miles from their home base. This was their section of the city. When I told them I was a blogger, writing about efficiency of delivery, the driver informed me that “Burp Brewing Co.” also had smaller trucks, which they used for lesser customers, like small restaurants, especially those with limited parking or maneuvering space for big trucks. (The truck he was driving, he informed me, could hold a thousand cases, somewhat more than he would deliver that day, and had been loaded in about 20 minutes.)

So there you have it. It can be said that his remaining cases had been on the road for at least eight hours to be moved 20 miles. (32km) That’s 2.5 mph. (average delivery speed = 4 mph, or 6.4km/h) Meanwhile two people are driving around in a huge, mostly empty, gas sucking truck. They will finish their day by driving the empty truck back 20 miles, a complete waste of time and machinery, where the truck just takes up space for other 14 hrs. before returning to duty. I would be surprised if the cost of the truck, insurance, space for storage, fuel, men, etc. is under $75 per hour, or $750.00 per day. If one assumes 10 hrs. for 1000 cases, that’s 75 cents on each and every case. “Burp Brewing Company” sells tens of thousands of cases a day.

This strikes me as directly analogous to problems with various forms of mass transit. The vehicles, buses for instance, must travel a large percentage of their routes nearly empty, and the many stops along the way create maddeningly slow commute times. Unfortunately, decision-makers tend to drive cars, so these inefficiencies are easy to overlook. The mother of non-invention is non-need. (Wouldn’t you love to make transit authority people commute everyday on the systems they manage?) Anyway this is not the case with commercial deliveries. Here decision-makers can make huge bonuses from incremental profit increases. A supermarket, for example, with a track running right into the back of the store could enjoy a substantial competitive advantage over stores that were not so connected.

When the Internet was first created, it was a limited network of limited importance. As businesses of all sorts started leveraging the technology, it became increasingly essential to be connected, just to remain competitive. Soon there were new business models that no one had previously imagined. I believe that the marriage of cheap computers, smart motors, and network communications is setting the stage for a transportation revolution that is far bigger than many, including many PRT advocates, presently (buuurrrp…) comprehend.

Sunday, October 11, 2009

54> SMARTS prt. 2

In the last post I introduced a catchy little acronym, SMARTS. (Small-scale Modularized Automated Rail Transport System) I’m not sure I like it, but it represents what I think is a good idea, the adoption of some open standards that others can build upon.

As I see it, the principle barrier that all PRT companies face is skepticism. Who can blame city planners and transit officials? The would-be companies come to the table with claims that they can build vehicles profitably, can build city infrastructure, including bridge-like track segments, can coordinate street traffic while utilities are being re-routed, negotiate the acquisition of right-of-way where needed, create a control system for these vehicles that is safe, build stations, maintain the fleet, collect tolls, etc.
“Gee that sounds like really fascinating technology,” Transit officials say, “Let me run it up the flagpole, and I’ll get back to you…”

One way to gain the confidence of customers is to have established standards and an independent standards body. After all, you need a license to practice medicine or even do plumbing. Anyone, however, can call himself a PRT provider. Standards creation is made difficult, however, by the fact that there are so many versions of what PRT should look like. I would hope that many of these providers would reconsider the highly proprietary nature their designs. Apple computer may have survived having it’s own standard, but that is certainly the exception rather than the rule.

I cannot champion all designs at once, and so I will concentrate on my own favorite, hanging designs, and more specifically the track, which is the part that needs standardizing most. This is because PRT companies might come and go, and vehicles will wear out, but the track is a very long-term investment. Even removal would be expensive. Cities need a “plan B”. Making a standardized, non-proprietary track that is cheap, simple and as versatile as possible seems like a worthy goal.


Here you see in the foreground the basic track shape I have shown previously. Just scroll down to my June 26th and July 16th posts for reference. I had mentioned in my last post that there could be various types of specialized track, such as low profile or industrial configurations that could extend the usefulness of PRT track. As long as there is some standardization, especially the slot width, there are many potentially useful configurations.


First, note that the track here is simple angle steel. It is shown as discontinuous so that it may be demonstrated that travel can be accomplished on a single side. The light brown hangers are produced from simple steel plate by a CNC flame-cutting machine. In other words, anyone can produce such track for little more than the weight cost of steel. For anyone who wondered, now you can see why my PRT track design has those hollow running surfaces. It is for flexibility in the support and steel thickness choices.


The picture above shows how simple a slower, more limited-range bogie may be. There are two aspects in particular which are not very practical in a PRT bogie that may be used here. One is the rims on the drive wheels (green), which hold the bogie in the track like a traditional railroad car. With high speeds, continuous use and quiet rubber wheels, these flanges would wear out. An alternative, shown here in violet, is guide wheels that are small enough to fit in the slot. In PRT, such wheels would spin over 5000 rpm, and would be too prone to heating and wear. Here I have redundantly included both of these slow speed options in a single bogie, for illustration purposes. Either would be OK for the occasional cross-town trip at reasonable speeds. Also note that there are no upper guide wheels, either for steering (blue) or centering. (violet) This is because this bogie is not designed to withstand the twisting torque of low-slung heavy loads on high-speed turns.

It can be seen that for companies to move goods around a factory, sky-hook style, is quite easy and cheap. It is not necessary to build full PRT track around the warehouse. Such a system could replace forklifts and conveyor systems, adding floor space. Goods could be moved between warehouses or to stores, increasing the usefulness of PRT track, especially at night. What is lacking, of course, is the software, which would be essentially the same as for PRT.

When we ask for taxpayer or investor money to build a network, that network should be very, very useful. Having certain key dimensions and construction details standardized just makes sense for everyone. An easy-to-remember acronym like SMARTS can’t hurt either.

Monday, October 5, 2009

53> SMARTS

I have been witness to the worst foliage season in recent New England history. It has rained almost every single day I have been here, and just been dark and cloudy the rest of the time. This has led to lots of time in the cabin, and I have had plenty of time to think, especially about the things the cabin lacks, like unending water and electricity and gas. It occurred to me that once upon a time, all water and fuel had to be delivered in person. This, in turn, got me to think about PRT as a pipeline, much like a utility. Actually I was mostly thinking about freight. Has anyone really analyzed what automated delivery would do for the world?

I personally believe that the big story here might not be, so much, PRT per se, but rather the automatic aggregation, transportation and distribution of physical objects, much like a the utilities I am presently lacking. Consider electricity from a variety of sources; wind, coal, hydroelectric, etc. It is mixed in the wires and sent out only where needed, where it is measured out into exactly what the end users require, where and when they need it. The utility can just read the meters and send out the bills. Isn’t PRT really the evolution of transportation into a similar model, except with people?

I have been hard at work trying to imagine a system that would work for people, mail, cases of cola, etc., and I’ve come to the conclusion that “one size” does not “fit all.” at least not with vehicles or their bogies. That is not exactly true with the track, however. I believe that a track design standard could be established that could accommodate various bogie styles and functions. In this approach the system would be highly modularized. Bogies would reside inside the track and various carriage styles for numerous functions would “snap” on. We could call it something like Small-scale Modularized Automated Rail Transport System. (That’s right. I invented SMARTS.)

I see something like four flavors of track, where for example, a PRT “pod” would be precluded from track that was primarily industrial, (it might allow extreme maneuverability, using super tight radii and cog technology for vertical travel) but the industrial bogie might use a public guideway. (Perhaps late at night) There could be a low speed, low profile, indoor (shroudless) track that would be for bogies that don’t require upper guide wheels, (too slow) but can be hug between the floors of buildings. There could be a very high-speed long distance variety, although I do not see it as being much different than ordinary PRT track, although the bogies would obviously be built for speed. (unless it’s fitted with Inductrack or something)

I will be posting more on this in the future, but for now, I am still out of town, and my laptop is ailing. (It crashed four times writing this, and won’t even recognize a thumb drive anymore) I will therefore get this posted, while this little library is open and this darn thing still works. That’s all from rainy NH.

Monday, September 28, 2009

52> 3D, 2D and Sky Hooks


I have been more and more confused as of late. It seems like there are so many competing visions of PRT, it’s almost impossible to define. A quick look at Wikipedia gives this seven point list compiled by ATRA in 1988.

1. Fully automated vehicles capable of operation without human drivers.
2. Vehicles captive to a reserved guideway.
3. Small vehicles available for exclusive use by an individual or a small group, typically 1 to 6 passengers, traveling together by choice and available 24 hours a day.
4. Small guideways that can be located aboveground, at groundlevel or underground.
5. Vehicles able to use all guideways and stations on a fully coupled PRT network.
6. Direct origin to destination service, without a necessity to transfer or stop at intervening stations.
7. Service available on demand rather than on fixed schedules.

There can be little argument about point one. Point 2, however, seems a bit restrictive. What if you want to detach the vehicle (cab) from the drive unit or bogey? “Why do that?” you ask. Perhaps the payload is cargo, not people, and you want the whole container. Another possibility is that of dual-mode, where the vehicle can drive away. An argument against dual-mode has been that if the vehicle was not well maintained, it could break down and clog up the system. If the drive unit, however, stayed in the track, a vehicle could be carried just like any other piece of cargo. Number 3 is, of course, subject to the previous argument. Cargo can help pay the bills especially in the middle of the night.
As per number 4. How small is small? To me the ULTra track seems like a full fledged road. I think the main thing is a commitment to 3D. (more on that later) Number 5 seems a bit arbitrary to me. My question is why? What is wrong with the possibility of private “spurs” that run into private property? It also seems possible that the track might come in various classes, such as a lighter, tighter turning version for industrial use. The passenger vehicles can obviously be “smart” enough to avoid going on such track. Number 6 and 7 seem fine, although again, one person’s attribute is another’s restriction.

I think it pays to consider that we humans have been largely earth-bound since the dawn of time, so that sometimes we don’t really recognize the nature of the problems it causes. Roads and cars are a 2D solution. Sure, we can build a bridge, or even a cloverleaf, but it’s still basically ground flattened to roll stuff on. Many of the definitions above are basically attempts at overcoming the shortcomings of being stuck on the ground. Isn’t PRT necessary primarily because there isn’t any more ground between point A and Point B? This seems especially true now that battery technology is enabling true electric vehicles. Why not just add six foot “electric only” lanes? Oh, yeah. No room.

Imagine a world with skyhooks, and you’ve imagined a world where all transit is point-to-point, on-demand, etc. The infinite PRT network. I like to think of the problem in terms of XYZ coordinates. Mary Poppins can apparently go anywhere within the atmosphere, but we must be content with the network of track and the capabilities of the vehicles they carry. Never-the-less, the ultimate objective of PRT, as I see it, is to enable a person or thing to be plucked from one place and dropped in another. Everything else is just a means to that end. Looked at in this light, it is clearly imperative that the track be as light and adaptable as possible, for this will ultimately determine how many XYZ coordinates the network serves and, therefore, its ultimate usefulness. In a world of so many competing PRT visions, let’s remember this metric for measuring their worth. We can call it the Mary Poppins test.

Tuesday, September 22, 2009

51> A New Kind of Motor

I want to say a bit more about motors. It has been my contention that linear motors are no longer the way to go for PRT, or at least won’t be for long. In a nutshell, when PRT was first developed, computing and networking were at their infancy and there was no choice but to control all vehicles from a single “mainframe” computer. Linear motors were ideal for that, since they were able to take commands from the track itself, and eliminated all of the moving parts but the wheels, and made vehicles immune to traction problems, even on ice. A “no-brainer”. The tradeoff was efficiency, both in use of energy and materials. (in the old days of motors driving chains, gears or belts there actually wasn’t any tradeoff at all) These http://www.blogger.com/img/blank.gifdays, however, enormous computing power can be cheaply employed on every vehicle, and increasingly, those energy wasting belts, chains and transmissions are being replaced by motors catering to the specific torque and speed needs of the machine. In other words, direct-drive alternatives are the coming thing. In PRT, direct drive means that the only moving parts are the wheels and this doesn’t change. These days there are low RPM, high-torque motors that are essentially like a linear motor but in a lighter, more compact, more energy efficient package. Like a linear motor, a direct drive motor can have regenerative magnetic braking. The one trade-off is that such a vehicle relies on traction being maintained between the wheels and the track. In this aspect linear motors are still superior. Therefore the following solution is only for reasonably clean and dry environments. (Shrouded track) Emergency stops, (i.e. There is skidding) can, if need be, be accomplished by clamping the track.

So that is the background, and to regular followers of this blog, that is all old news, as is my love affair with wheel motors. (motors wherein the axle stays stationary and the motor itself revolves) So here is how all that background ties in.

I got to thinking about what specifically was so good about wheel motors and realized a couple of things. First and foremost is that it is a direct drive solution. Secondly, it is the form. Wheel motors get hi-torque and high positional resolution from having large diameters, with many magnetic poles. Generic motors generally get more torque from being made longer, a shape which is not well suited to PRT. I therefore (with the discontinuation of a number of wheel motors from PML) started looking into alternatives with search words like “flat motors,” “pancake motors” “high-torque” etc., and found a kind of motor which was new to me, the “frameless torque motor,” Illustrated below. Although it’s inner ring (rotor) turns instead of the outer, like a wheel motor, it can be housed in such a way that it will still provide true direct drive. One advantage to this motor is that the PRT designer can use readily available, standardized, replaceable automotive bearings.



I am a bit disappointed by the upper speed of the air-cooled models, however, as I was with PML’s wheel motors. A quick look at my drive unit of July 16th shows relatively large drive wheels, which, quite frankly, crowd the track, which is already taller than I would have preferred. (I would like the track and vehicle to be able fit in a building between typical floors, if possible, and, in my wildest dreams, two high under a highway overpass) Slow rotation necessitates large wheels to get speed. For example, to achieve a speed of 60 mph, (96k/h) a 14” (356mm) wheel must turn at 1440 rpm. This has been sort of a sweet spot for me, design wise, because I doubt that it would be beneficial to make the drive wheels much bigger or smaller, and I doubt any initial PRT iterations would go any faster.

The wheel diameter and motor speed information, together with presumed assumptions of adequate acceleration, form a sort of triad, which can be adjusted to size the motor and track. (In the June 16th post I showed how the track size could be decoupled from the truss size; The track itself need not be self-supporting over long spans) The track is, of course, the big kahuna of PRT design. Little pods may come and go, but the utility of the track design will be debated for generations if that track design becomes the de facto standard. It can be said, therefore, that it would be silly to base track dimensions on some arbitrary motor specifications. After all, motors can be custom wound. But, hey, wouldn’t it be nice to base track specifications on readily available parts?

To the minority of readers who are even remotely interested in form factors, torque or speed ratings of motors, I would refer you to http://www.etel.ch/torque_motors

Finely a bit of personal news. As of tomorrow morning at 4:30 AM, I will be on route to New Hampshire, (USA) to close up my cabin for the winter, and take in the magnificent fall foliage. There is no internet, or even electricity to speak of, since I am a half mile from the nearest telephone pole. I can plug in at the town library, though, and hope to post at least once in the next few weeks. So “bear” with me, if I am slow to comment or return Emails. I’ll try and post a picture
- Dan The Blogger

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.

Saturday, September 5, 2009

49> In Search of Gridlock and Opportunity

I have, for the last couple of posts, been trying to figure out how various PRT designs would fare with limited track and stations. My quest deals with the recognition of the fact that no investors in their right minds would sponsor a full network as a trial. (I am not abandoning the possibility of private money just yet) Like it or not, we have to look for the most cash flow from the least network. This exploration has led me to recognize the fact that a few dispersed low capacity stations may not introduce passengers to the system fast enough. Paying passengers must come from somewhere. If they do not come from dozens of smaller stations, then they must come from a few larger ones.

I understand how PRT is supposed to work. It is not a hub-and-spoke, mega-station type of technology. Nobody has described PRT vehicle storage because it is not supposed to be required. But if there is any way some track can be put down, and some vehicles deployed, expansion could start from there. The “foot in the door” it seems, would need to be some situation where people are so inconvenienced that they would be happy to pay a premium to take a short ride.

So here is a building block. This is a bare-bones seven-berth station that can have a 60 second turnaround time. (In one minute all berths have been loaded and moved out, and a fresh set of vehicles has taken their place.)

This illustration shows a high-capacity station comprised of six of the seven-berth stations arranged in parallel, with three boarding scenarios. The arrows indicate foot traffic. The first (A) shows how the station could be adapted to accept a majority of passengers who are boarding. Green lights or programmable signs would direct passengers to berths. Red lights would indicate that people are disembarking from that area. The middle figure, (B) shows a balanced load between incoming an outgoing vehicles. The last figure (C) shows the station accepting large numbers of incoming passengers with few heading out. Green lights mark the three berths accepting passengers. Such a station could, with the 60-second turnaround time, process 42 cars per minute or 2,520 cars per hour. (Note; This uses the gondola design: bottom track designs would require a means to get passengers to the boarding areas without crossing tracks.)

The illustration above shows a “hub and spoke” system with the main station connected to six satellite stations. In this scenario, the time required to completely empty the main station is one minute, the same as the satellite stations. For the sake of simplicity, let us assume that the satellite stations are a half-mile from the main station and that the travel speed is 30 mph. (I originally designed this to take people from a stadium to satellite parking, so that’s why the distances are so close) The number of stored vehicles is 42, so that with the 42 in berths and the other 42 from the satellite stations, the stations would never run out of vehicles. (126 cars total)

These examples point out a few key concepts. First, it is a closed system. PRT advocates tend to see PRT as an open-ended network, with an endless supply of vehicles, which will always self-balance. (i.e. a BIG network) In this example, all stations would run out of cars in 60 seconds, were it not for the stored ones. It is only the close proximity of the satellite stations that allows replacements to get there in time. For every additional half-mile, another 42 cars are needed.

More can be learned from the example. With only 3 miles of track, it is extremely limited, yet it would still probably cost over 30 million dollars. Could it pay for itself? One thing worth considering is that the full capacity would only be utilized for, perhaps, 3 hours per day, 5 days a week. If the cost of money were, say, 10%, the daily interest alone would be $8,219. What price point and usage pattern could bring in, perhaps, $13,000. to put the project solidly into the black?

Again, I designed this for a stadium, where the time to just get the whole family into and out of the parking lot would justify some very high fares. (not to mention that 90% of the track would be on private land) After checking the schedule of a local stadium, however, I realized that these big events are so infrequent that the system would never be viable, even though it could generate upwards of $40,000. per event. I now put it forth as something to ponder only. If the main station was broken into two or three, and the system stretched a bit, it might cut driving time by 10 minutes each way for some particularly congested downtown areas. My logic was to think up a scenario where passengers would gladly pour into a super cheap station to hardly go anywhere for top dollar. Investors, after all, are not known for altruism. We can all imagine a fully-grown, distributed PRT network. Can we come up with a viable PRT seed? For, say, 30 million?

Thursday, August 27, 2009

48> PRT Stations...Continued

Almost immediately after posting last week I realized that loading cars one at a time was probably not what the designers of “taxi stand” (serial) stations had in mind for crowded situations. By loading a group of PRT vehicles at once, they may depart as quickly as the leading vehicle is ready, a fact that was quickly pointed out in the comments.

In particular, alert reader Akauppi added a link to a fairly comprehensive study of the subject by Peter Muller of PRT Consulting, who pointed out that numbers of simultaneously loaded vehicles could depart in “platoons”. The study concentrated mostly, however, on what he termed “open guideway systems” such as Ultra, because of the many ways they may be maneuvered. (These systems are essentially automatic cars, and may be parked and boarded in any way a car can.) In a statement reminiscent of criticisms that I have also made, Muller states, “Captive bogey PRT systems, such as those being developed by Vectus and Skyweb Express, show little variation in station design. The stations are always off-line, and the bays are always arranged in line with each other. This lack of variation probably results from the intended relative high capacity of these systems and their inability to accommodate tight radii.”

The obvious countervailing argument is that those “open guideway systems” fail to address one of the obvious benefits of most PRT systems, that being reduction of roads. We are rapidly coming to a time when we will have electric cars. Does separating precious real estate for less nimble automated ones really solve anything? Isn’t a separate road less efficient than just widening the one that’s already there? Well that’s a different subject, so I will return to what he terms a “captive bogey” system. (Pod on top of a rail.)

I did have one idea on this subject, which I have not seen, and that is this. The necessarily elevated stations, such as is required by the PRT International and Skyweb Express systems, must include an elevator (for the disabled) a feature I have criticized in the past as not being repeatable throughout the suburbs, for cost reasons. I think it noteworthy, however, that such a system, in the inner city, may have a very small footprint at sidewalk elevation. The sheltered area below the station might actually be an asset, as it could house news or food stands, or other sidewalk vending, at a natural spot for pedestrians to congregate. (No, that’s not the idea.) The idea is this. The “offline track” can be further split in two with the elevator in the middle, its structure supporting both tracks and a common boarding area, which needn’t cross any track. It would look something like this.

In this picture the large E is the elevator, which has two doors, ED1 (elevator door 1) and ED2. This is how it would work. The elevator, at street level, would open ED2 and passengers would be lifted to the boarding area, and ED2 would reopen, letting them board. ED2 would close and ED1 would open to let arriving passengers into the elevator, which would descend to street level and open (ED1) to let arriving passengers leave. ED1 would then close and ED2 would open, starting the process anew. Back on the boarding level, green and red lights, or even gates would be indicating the available vehicles, starting at the front of the line. The vehicles could move out as a platoon or the front vehicle could start out when ready. Once passengers have disembarked the vehicles on one of the tracks, the now empty vehicles in the arrival area would move up (to the boarding area) as a group.

In a hanging (gondola) system, a similar design can be used at street level, without the elevator. Very highly trafficked areas could have an elevated level as well, so that the station would, by the berth count illustrated, be capable of 12 simultaneous loadings and 16 unloadings.

Finally, here is a depiction of dual docking track described above, but with the “saw tooth” boarding scheme favored by Mister and Ultra. (fig. 1) Note that passengers may either board or disembark from any berth. The saw tooth design, being inherently parallel, gains less from splitting the track into two than does a straight line (serial) arrangement.

Actually the long, narrow footprint of a single row of berths probably fits better into the available space of most sidewalk environments. (fig. 2) Each vehicle may leave immediately after boarding, but both departing and docking vehicles may have to wait for each other because this system requires backing up into potential traffic to leave the station. A good way to control traffic would be alternate between groups of vehicles entering the station and groups leaving, (like the previous example) rather than a pure “first come, first serve” basis. In Muller’s study, he suggests that all vehicles can pull out together, ignoring the issue of vehicles not being ready at the same time. I would suggest perhaps three at a time. (In fairness, he showed a three-berth station) I should also note that with a gondola design, with no slots in the floor to step into, open-air stations could be extremely cheap, and therefore positioned with much more frequency than other station designs I have considered, and therefore could be made with fewer berths. (I am a big fan of cheap stations) Going back to the original, hypothetical three-station loop, however, it would seem that “platooning” is increasingly advantageous as traffic increases, but is a drawback if the traffic is minimal in “saw tooth” stations. Note that in this system, the berths are not exactly equal. Vehicles in the front berth, for example, would have little problem leaving but when empty the front berths could have slower vehicle replacement times. The opposite would be true for berths in back. Optimal traffic management for very busy stations would seem to be relatively complex. It is not immediately apparent to me if the saw tooth design would have better throughput than the dual track strategy outlined above, but I think it would out-perform the single line “serial” designs (PRT International, Vectus) with ease. I would also point to the variation of the saw tooth design I pictured in the last post, would not require platooning but requires rapid elevation changes in the track to avoid pedestrian/vehicle interference. It would seem to call for a comparatively large station, if the number of berths was, say, less than eight, but would be a very compact and efficient way to arrange a dozen or more berths.

In conclusion, I would reiterate the observation of the last post, that in order for PRT to be a valuable transportation alternative in initial limited and trial situations, high capacity stations are a must. In these posts I have explored the ideas of boarding and departing in groups and splitting the offline track as a means of increasing station throughput. I have not exhaustively studied every possible way to achieve simultaneous parallel “processing” of passengers, but it seems that PRT can have passenger turnover rates approaching group transit alternatives.

I also believe that a mix of both high capacity and very inexpensive suburban stations or stops is required to have a system capable of reducing commuter traffic, and that most current PRT designs do not meet this test. I hope that consideration of these station alternatives will prompt a reexamination of PRT vehicle design, especially with regard to both vertical and horizontal turning radii.

Alert read cmfseattle sent us this link to an article written by Bill James, (Jpods) a fellow who has come up with some designs (track and bogey), which are so much like mine it’s spooky. (And he seems to have done it first, but who is counting?) What is very cool is his trademarked term for PRT, the “Physical Internet.” Very descriptive, don’t you think? Let’s agree on something just that versatile and unstoppable.