PRT and the Art of Cabinet Making

I want to say a little more about other uses for PRT technology besides moving people. Freight has long been contemplated, and looks attractive as an after-hours revenue generator, but has the same critical mass problem as carrying people, only more so. Only after there is an extensive network is it of much use. In the last post I said that the concept of SMART (Standardized Multi-axis Automated Rail Transport) applied to more than Automated People Movers. Well, it also applies to more than freight. It applies to anything and everything that needs to be picked up at point A and sent non-stop to Point B within a matrix of possible origins and destinations that are most efficiently accessed using 3D routing. A prime example is manufacturing.

 

The images above represent a greatly simplified assembly line. On the left six parts (in red) are added to a product moving along an assembly line (blue) in various stages of completion. The right side shows what happens if the product comes in just three variations. No extra parts, just some hypothetical process variations at the points where the blue lines diverge. Now, when same parts are added, paths must cross. If this is done on an actual work floor, this crossing is quite literal, causing someone to wait, go over or go under. This situation is usually handled by stockpiling supplies, so such crossings are less frequent. But consider how this solution is analogous to city buses. They can move many passengers through an intersection at once, but are big and cumbersome. Of course we know what happens beyond a certain critical mass. At some point, anything other than full-speed, non-stop movement will create a cascading gridlock effect. If the parts are bulky, stockpiling them may be impractical in any case. So with that in mind, consider the illustration again, but this time with dozens of variations, instead of three, and many dozens, or even hundreds of parts, instead of six. This makes routing and staging parts and positioning work areas a real nightmare. It would take me a week just to draw it!

Some years ago, back when CNC was a brand new thing, I was given a tour of a cabinet factory. The main feature that you couldn’t ignore was that the place looked like it was designed by an insane ski-lift maker. There were cabinet pieces floating past all over the place, some hanging on hooks, and some in baskets. These were all going in different directions, all guided by long moving chains hanging at various levels from a superstructure attached to a very high ceiling. It was quite a sight! I think cabinet making is a simple enough process that hopefully it will help me illustrate my point.

The cabinets largely started as 4x8 foot sheets of material. You see, the secret to cabinets is that there are very few changes in saw settings. Be it a 48” or 24” cabinet, the sides, for example, are the same height and depth. And since most dimensions are repeated again and again, it only makes sense to set various saws one time and cut large numbers of pieces. And so it was in this factory. Material came in on forklifts and was rip-cut to various standard widths. Then those pieces were cut to lengths for the various sizes of cabinets. Most of the pre-finished pieces would go directly to an assembly area that was just for one or two specific cabinets. So there were many assembly areas. But cabinets come in various paint or stain finishes. All face-frames and doors and drawer fronts for a specific order, therefore, had to go through a finishing process. So they needed to be collectively detoured to a finishing and drying area and then re-sorted by sizes and sent to their respective assembly areas where they would join the prefinished parts and preassembled drawer boxes, which would be made still elsewhere in the factory. After assembly, the finished cabinets would be push on roller tables to a nearby boxing station, and then grouped with other sizes to make up an order or truckload. Cabinets come in four or more standard sizes, along with corner units, sink bases, and banks of drawers and all sizes have corresponding upper cabinets. And if all of this isn’t enough, let’s not forget the number a door styles that are typically offered!

Now consider all of this this against the illustration, and you will appreciate the problem. There were many dozens of work stations, some organized by component, some by cabinet size, some by finish, and some by purchase order. The only way to move things around efficiently was to have skyhooks that would whisk parts to the proper station, and do so without clogging up the shop floor. Cabinet parts would go around and around until someone took them down.

The same root causes of traffic on streets are the dilemmas that the cabinet factory suffered. These are generic problems that come from conflicting directional movement on a 2D (ground level) surface. As I think I may have mentioned in a previous post, the same problem extends all of the way down to circuit board and even computer chip architecture, and I have been told that there are aspects of graph theory that are used to help solve these difficult issues. Planning a factory, it seems, is a real science. I read somewhere that the Chevy volt assembly line is over twenty miles long. They are probably counting production lines for the sub-assemblies, but still this gives you an idea of the scope and complexity of this issue.

PRT grid would be used to prioritize pick-ups and deliveries around the factory floor. Every stockpile of pieces or sub-assemblies at every workstation would be automatically replenished, and then the resultant parts taken away to the next staging area. PRT traffic management, it turns out, is very close to industrial process management.   

We are in the early stages of the robot revolution, and most are still essentially mechanical arms bolted to a floor. Any work piece has to come to them. Lately, however, some are becoming more mobile. Gaining popularity is what is called a gantry robot, because it can move itself along an overhead beam. But these are still tethered by power and data cables. While these robots are handy for assembly, because they can fetch parts, they can only go so far. The next logical step is the untethered “railbot.” This has not already happened, in part, because the key to maximizing the effectiveness of such a system is to make it route-switchable, electrified rail, but still with full data transfer capabilities. (Gee, now where have we seen that problem?) Make no mistake, this is coming to manufacturing. Non-switching, somewhat limited versions of such overhead “railbots” are already used to lift and tilt cars during assembly, as shown in the picture below.

 Refrigerated warehouses already use similar machines to fetch frozen foods without requiring humans to work in the cold. The PRT maker 2getthere is a subsidiary of company that makes self-navigating forklift type vehicles.  Making a grid over the factory floor and extending track all of the way to remote warehouses promises to make an extremely efficient and versatile manufacturing platform. Remember, the overhead bogies can either carry materials or have their own robot arms or both. As long as the bogie can be made to precisely locate itself and then lock on to the track, it’s suitable as a base for a robot arm. In the case of the cabinet shop, for instance, the assembled cabinet faces would be not just carried into the finishing room, but held for spraying and delivered to the drying area without human intervention. We are talking about an amazingly flexible system here.

The holdups to deployment are very similar to obstacles facing PRT. Like vehicle makers, robot makers do not really want the business of constructing track or controlling traffic, since that would demand a totally different, more locally oriented business structure. And track fabricators certainly don’t want to get into the robot or vehicle business either! Some great ideas just don’t fit with existing business structures.

That brings us to a point about the “S” (for “Standardized”) in SMART. One key is to have a standard track-to-vehicle interface, so these businesses can concentrate on what they do best. Currently, assembly line equipment is generally a huge, one-of-a-kind investment that may well go to the scrap heap when it is no longer needed. Meanwhile, product life cycles are, in case you haven’t noticed, getting increasingly short.  A modular solution can be reused, reconfigured, and even eventually sold off at a reasonable price, like any other equipment. But modular pieces need to fit together, and that means a degree of standardization.

There was a time when getting a computer meant special rooms and teams of engineers to hook everything up. Over time, the system evolved into a something much more modular, and therefore flexible and simple. What geeks call “plug and play” is, no doubt, the destiny of automated manufacturing as well. It just happens that we, in the world of PRT, have long contemplated and largely solved the problems that they, in manufacturing, are just starting to understand that they have. And did I mention warehousing and package sorting?

When I talk about needing non-profit organizations, government grants, academia and corporate partners, it should be kept in mind that there is a lot of benefit to taking part in this transition. Self-navigating, non-stop 3D transportation is the ultimate in efficiency, both in terms of time and energy consumption, and this, in one way or another, will always mean profit. This application, unlike PRT, is for a closed, private sector application where there are a huge number of companies that might benefit. When I talk about an NPO umbrella for all of this, let me just say this: (I would refer the readers to the previous post for background)

The companies who would benefit the most from this technology need some kind organizational framework that enables them to participate and keep abreast of the work that others are doing. The tax exempt part of this really isn’t the point for these players, they can write everything off anyway. But I can see absolutely no reason to make this framework anything but an NPO, especially early on. This is not really anything revolutionary. The world is awash with such consortiums, and it would, in practice, be nearly impossible to equitably divide up any profits anyway. (An example of a for-profit consortium that had profit dividing problems is the original Airbus, and an example of a large NPO type consortium for advancing technical expertise is Sematech). This particular endeavor, I might add, also has a lot of “green” and “public good” aspects to it, and so would be well situated to raise money from individuals, charitable organizations and governments, not to mention possible participation from universities… I mean we ARE talking about saving the planet, after all…

And yes, I realize that this whole thing, at this moment in history, is an audacious pipedream. I also know that every revolution has to start somewhere. For lack of a consortium, I am, at least for now, willing to do its work singled-handedly, at least in respect to exploring the pros and cons of various design choices. A consortium of one!

I guess the bottom line here is that the ability to “airlift” many objects, non-stop, in a coordinated way, is a very big deal in many human endeavors, not just people. Robots are becoming more mobile and modular every day. So remember, you heard it here first:  Railbots are coming to get you! (at your local station, of course!)  

Imagine

There is a problem with the PRT business model. It is not scalable enough to really make an impact, because it is inherently a multifaceted local endeavor. For the foreseeable future, each new project will tend to dominate the PRT provider’s attention, at least until it is up and running. That is just how construction and development based projects are. This is not to say that a PRT provider cannot grow big enough to handle multiple projects at once, but rather to say that such growth cannot be rushed.

There are models that offer at least partial remedies. For example franchising might have potential, and partnerships offer another avenue for more rapid growth. The normal way rapid, revolutionary change usually occurs, however, is from the bottom up, where many self-serving actors can chip away at a problem independently. So how can this be done in the PRT world? 

Well, for one thing, whatever oversight is required must be kept to an absolute minimum. McDonalds didn’t get so big by trying to manage the day-to-day affairs of individual restaurants from the central office! So what would this minimum be? Let’s start with a process of elimination.

First, the track - which certainly would involve a lot of local collaboration in any case. It is my belief that track can be installed for under 2.5 million USD per mile, and that the lifespan is such that only a small fraction of the fares would be required to pay down these costs. So can this constitute a viable, stand-alone business? Let’s run some numbers. Imagine we are counting passing vehicles on a one mile stretch of track and on average, during a sixteen hour day, there is just 1 passing vehicle every ten seconds. If the track provider gets paid just 12 cents each, that is $691 daily, or over $252,000.00 annually. That is enough to pay the track off in about ten years. The track should have a life span of many decades, so after it has been paid off, it represents a pretty nice little cash flow! So far, so good.

Let’s turn to stations, and let’s assume that private land is involved. If landowners can make a small piece of the fare, say 20 cents per passenger, and station construction is a turn-key proposition, (probably by being an add-on contract for the track guys) then perhaps this too can be a standalone business model. Let’s assume a low volume, bus stop style station that can be built, including some feeder track, for $150,000. It has an average usage of only one passenger per two minutes with the station getting 20 cents of the each fare. That’s over $35,000 annually, so the station could be paid off in under 5 years. (To make this still more lucrative, local property tax inducements could be offered as well, something that most cities could pull off without a lot of opposition. Also, let us not forget the value of the increased pedestrian traffic to the landowner.

The vehicles are probably best made by a consortium of really big companies that want to gain good will and free advertising while making a buck in the meantime. Once again, a piece of the fare would go to this effort. I say consortium because, at least as I envision it, the part of the vehicle that is not the passenger compartment is essentially a mobile robot, and might fall better into the expertise of the people that build the automobile assembly line equipment than the vehicle maker per se. Readers of this blog will appreciate that my vehicles seem quite ambitious; however even a few cents per mile buys a lot of vehicle over years of daily service. For example, at 11¢ per mile (100 daily miles) and $0.45 per passenger, (say 50) a vehicle would generate $33.50 daily, which comes to $12,227 per year. At, say, $60,000 each, that is still only a five year payoff cycle, and these vehicles ought to have much, much longer lifespans than that.

So what are we up to? $0.65 to board and $0.23 per mile?  I guess we better add 13 cents a mile and a nickel for station maneuvers to pay for electricity. OK. Now we’re up to $1.06, and we haven’t included maintenance or monitoring, or even finance costs, but this is not supposed to be anything like a real feasibility study, and I want to get on to the next part, so bear with me.. (I’m not sure that some of that can’t be passed off to the local transit authority anyway, but let’s not deal with that now…)

As I said in the beginning, the way to make a system rapidly expandable is to allow bottom-up, decentralized growth, by minimizing or even eliminating the responsibilities at the top. Obviously there is a lot of coordination involved in PRT deployment, and this area alone could be the subject of many, many posts. Let me just say, though, that I envision the top of this totem pole to be a non-profit  organization. (NPO) Such an organization would develop the standards necessary to allow compatibility between the disparate corporate players and work to improve the system over time. The organization would also work with local transit authorities, provide training, etc. I would note here, for those not familiar with NPOs, that they can behave very much like for-profit companies, except they do not pay taxes. They have salaried management and staff, can award contracts, etc. It is my assumption that there is some way to levy a fee from PRT fares to help support such an entity, either directly or indirectly. Any lawyers out there? The NPO would play a key role in developing the system by soliciting help from academia and industry, as well as fund raising and promotion.

If all of this seems complicated, compared to just forming a PRT company, let me point out that an NPO has a definite advantage when it comes to raising funds and issues of trust. Person(s) seeking to create a for-profit PRT company can still do so while being affiliated and perhaps even drawing a salary from the NPO, although conflicts of interest must obviously be carefully avoided. Right now PRT companies are starved for R&D money. That is because they want to have all of the profit for themselves, and the result is products that look like they were… er… starved for R&D money. I would suggest getting a smaller part of a much bigger pie, divesting one’s self of the parts of the PRT effort one doesn’t want in the first place. A great deal of this stuff is, after all, clearly in the public interest. But government and private grants have a real problem going into PRT development projects since there is no entity to receive them, except for-profit corporations whose fiduciary responsibility is the enrichment of their shareholders.

Standardized Multi-axis Automated Rail Transport - (SMART) - That is my take on what is worthy of public research and development funds. The concept is simple. We need an all- weather way to move objects longer distances in full 3D rapidly and efficiently. 3D because our surface world is too crowded to permit non-stop movement, and getting to and from ground level needs to be as easy and straight forward as possible. This is not just about moving people, but rather the transit solutions are a sub-set of SMART development. Other areas of development could include warehousing and freight delivery, for example. The common denominator between all such subsets is the multifold increase in energy and time efficiency, something all responsible citizens and their respective institutions should want to support. 

Movement of people and freight is at the very foundation of society itself and the efficiency of our means of transportation are paramount to the prosperity of every one of us, not to mention the sustainability of our, and every other, species on this planet. I can see no other effort so worthy of philanthropic,  government, and corporate support. Now I know the numbers I throw out above are hardly worth the paper they aren’t written on, but the ridership numbers are, you will agree, very modest, and I was, after all, just trying to get readers thinking. To make this work, the independent business models have be so lucrative that they are like taking candy from a baby. Independent businessmen need to have enough to gain that they will relentlessly pursue each available lucrative route. The object is to iron out every legal, fiscal and technical challenge and lay the opportunity at the feet of free enterprise. I know this is a huge challenge, but what other scenario is out there that would enable hundreds of cities, worldwide, to start building PRT infrastructure at once?

Imagine that. 

Playing Monopoly

PRT is a confusing soup of construction, computing, vehicle manufacture, public works, system maintenance, and a bunch of other stuff. It is a complicated business model and it is difficult to estimate costs. What is worse, there is a tendency for would-be providers to estimate costs on a per mile/kilometer basis, which further confuses things. After all, vehicles, track, stations and control each have their own costs, lifecycles, and logic. Building vehicles, for example, has very little in common with building track or stations. The “per/mile” estimate is especially problematic in view of the landscape we face in the US. Here, our cities have grown into a suburban sprawl that has little consistency in terms of the placement of destination-rich areas.

To help the reader understand how this came to be, let me recount what was told to me, back in the seventies, about a little “up-and-coming” real estate developer, Trammel Crow. His formula for success, I was told, was really quite simple. First, find a growing city. Take the main road out of town until the land is sold by the acre, instead of by lot, and by some frontage. Build a tilt-slab office/warehouse on it, put it up for rent, and wait. It reminds me of playing Monopoly. Instead of using all of your money to buy Boardwalk, you can buy the cheaper Baltic Avenue, and “develop” it with houses instead.  In either case, though, you buy and hold, while investing as much as you can afford to make it into an income producer in the meantime. This is instructive in understanding how cities develop such dysfunctional layouts. Land developers are, underneath it all, land holders, and often simply have something minimal on that land to pay the taxes and generate a little income while they wait for it to appreciate. This also helps to explain the vast parking lots that take up so much of our cities. Only at Christmas are they anywhere near filled. The land owners simply don’t have the money to build and maintain anything more ambitious. Even if they have the cash they are more likely to buy additional land and do the same thing elsewhere with those funds instead.  Anyway, this has helped contribute to retail outlets that are big and far from the road, and getting from one such store to another is often not a walkable distance. This effect is also coupled with the effect of freeways, since freeway frontage offers an ideal place to exercise that Trammel Crow model, except the lease is to “big box” retailers, who have discovered that economies of scale are more easily exercised away from the expensive downtown areas.

When it comes to walkable, integrated urban/suburban environments, it is usually the old parts of town that shine. Little towns that get absorbed by cities usually retain their main streets and hopefully a bit of their charm. But these, too, are “destination islands” in a sea of sprawl.

For a PRT system to be a viable way to get around, it has to go to these important destinations. If they are in clusters separated by substantial distances then this strongly suggests a PRT design that allows more than a single speed. It suggests a design that is similar to how freeways work, where there is a slower feeder that runs parallel to the faster main highway. This is because the deceleration and turning are disruptive to the faster, distance-oriented thru-traffic. In the case of PRT serving disparate, clustered destinations, it is possible that the best design might be for the local, feeder system to be quite slow. This would allow an absolute minimum of the double track required for off-line stations and allow for extremely tight turns. Faster track would connect these destination clusters.

This ties in with the discussion of land development and PRT cost estimation in the following way: First, it is important to get some kind of handle on the costs of running track alone. The downtown PRT models tend to assume blanket coverage for a pedestrian rich area. In the case of destination-rich freeway frontage, the proportion of stations and vehicles per track distance would seem similar, being based on walkable distances, although it would be linear, rather than based on loops covering city blocks. The “old town” destinations, referenced above, are classic downtown loops, just scaled back to one or two. But connecting all of these (and the actual central business district) is fast track. So when figures like ten to twenty million dollars per mile get tossed around, it is highly misleading. I would guess this stationless track, on public easements, would be more like 2-3 million per mile. This fast track could easily pay for itself, it would seem, by virtue of the fact that it would cut through so much traffic.

Those “big-box” destinations tend to have that extra parking lot space, and this would seem to be a great place to put PRT stations. But the land is rarely owned by the retailer, and therefore it makes little difference if that retailer wants to provide PRT access or not. The land owner has his own agenda, and understanding his wants and needs is what counts.

The first thing to consider is that he won’t want to give up sovereignty over a single square inch. That means anything permanent is problematic. At present, the advantage of hosting a PRT station is only theoretical and it cannot be expected that this is all a landholder would want at this time. This is especially true if there are excessive requirements for utilities, permits, digging and the like. On the other hand, the land in question is often of very little immediate value to the landowner, since building anything large on it would block their main tenants’ visibility from the street. So it comes down to that ultimate grease to getting things done – profit. How can the land owner directly make money by having a station? It is pretty obvious that in an ideal world, the pedestrian traffic generated by the station would be coveted by the tenants to the point that they would pay greater amounts to lease their stores. The landowner would therefore willingly give up the rights to enough space for a station. Let’s keep our optimism in check, at least for now, and say we have to sweeten the deal.

In theory he could get a small piece of every transaction, and there is also the potential for parking revenue. The amount charged couldn’t be much, because otherwise people would park for free in the guise of being store customers, a potential problem with almost any good transit system that is close to retail outlets. But if the parking is right next to the station, and the station is easily removable, and there is nothing for the landowner to do but collect money, I think there is potential. Electronic payment means can integrate parking fees and PRT fares into a single transaction.

What is good, though, is that this helps solve a major problem of transitioning from a car-based to a pedestrian based cityscape. Absent a real “last mile solution,” PRT could still make a huge contribution to traffic reduction. If the system doesn’t get to your door, it should at least get to your grocery store.

This all begs a bunch of questions that need to be addressed in a future post. Specifically, we need to examine further the issue of decoupling the stations from the track, from the vehicles, from the control. Each has its own rate initial costs, rates of depreciation, etc. Varying the ratios between them greatly influence the profitability of any venture. Can a bunch small stations be used in place of a bigger one? If we are going to bridge a bunch of destination clusters, how far apart is too far? Can the business models for each be separated and therefore simplified to be made more attractive to investors? We’ll get back to this. Stay tuned!

Hot Rod

My Pappi said, "Son, you're gonna drive me to drinkin if ya don't stop driving that HOT ROD LINCOLN!"

As long as people build and ride vehicles, there will be those of us that want to soup them up - to push the limits of acceleration, climbing power, or, more often, just plain speed. Personally, I am a student of structural geometry. From crystal lattices to geodesic domes, I have always been intrigued by the myriad ways shapes can placed and connected to swivel, slide, rotate, hold, reinforce, depress, hinge, stretch, bend….you get the idea. I just can’t look at a mechanism without dissecting every component piece to understand exactly why each surface and dimension is as it is. So when confronted with PRT, I really just can’t help myself – especially when that geometry limits practical functionality – even to the point that the whole concept struggles to find acceptance.

It is a fact that whatever form a new technology first takes becomes the de facto standard. Currently that PRT standard is the robocar model, and so cities considering PRT are looking at those requirements and limitations and making decisions accordingly. Road racing pushes the limits of automotive design and the military pushes the limits of aviation. If I don’t push the limits of PRT design, who will? And how will anyone ever know what PRT could really do for society without someone figuring out what the technology is really capable of?

In my quest to push back PRT’s limitations, I have made the following observation. PRT has been generally designed with the assumption that the track or guideway is continuous and equal throughout, except where it forks. 

It is easiest to conceive these systems from a head-on view of the track’s running surfaces and corresponding wheels, as shown in this patent illustration. (Anderson 1985)  The parts get arranged to enable the greatest capability possible. Job done. But wait! Those capabilities can be exceeded, and this is how.

The track’s running surfaces can have variations of all sorts for different purposes. Furthermore, the vehicle or bogie need not use the same wheels or guides for every purpose either. When you combine those two concepts, a lot of limitations fall away and new possibilities arise. You can turn that stuffy old PRT design into a real hot rod!

 

Let’s start with some main drive wheels and some guide wheels to keep them on track. This bogie is for a suspended system, so it is upside down from the bottom supporting design shown in the Anderson patent. This triangular geometry is designed allow for a  minimum number of the larger, longer wearing wheels that are much preferable for high speeds. (The guide wheels in the Anderson design are limited in size to one half of the track width.) There is an unfortunate side effect however. Those angled guide wheel running surfaces are cumbersome to work with in curves, especially the serpentine routing that would enable system designers maximum flexibility in tight spaces. This is where it pays to remember that the track can transition. Here is a simple transition from double angle iron to pipe. There are many other ways to accomplish the same thing.  

 

If the whole system used pipe, like on roller coasters, the wheels would wear in the center first, and more quickly need to be readjusted or replaced. By using the first configuration for straight runs and only using the pipe for curves, the wheel life can be maximized. After all, we hot rod guys know a thing or two about going through tires! I know that some of you are thinking that some miracle plastics out there can last a very long time anyway, and so this is all a wasteful complication. The problem is that noise and vibration are (roughly) inversely proportional to wheel hardness. Softer, quieter materials will always wear more and rob a bit of mechanical efficiency but that’s just a compromise that we have to live with. I suggest making the architecture capable of whisper-quiet operation first and then going with the hardest wheels that we can get away with.  

Below is the concept adapted to ride on half of the track, which avoids the notorious “frog problem.” (unsupportable track area that results from “Y” interchanges) The additional bottom wheels (shown simply floating in space) in this position must be smaller and so would be the first to wear out but for the fact that they are not needed continuously. Then there are the upper wheels, which are designed for continuous contact, but are under minimal load, and so can be relatively skinny in profile. There is a pair of retractable upper guide wheels that, like the middle bottom ones, are only used for switching. A couple of notes: The top section shows a bogie that is not in an interchange. The bottom two show the running surfaces having split further apart, as would happen in a “Y.”  The sprockets shown are for climbing, cog railroad style, not for driving the wheels, which drive themselves. The wheels are all independent, including the middle flanged wheels. As always, click image to enlarge.   

 

The point to all of this is that there is a much higher inherent speed limit to such a design. Using wheel/hub motors there is room for over 300 hp worth of pure hot rod power, and these direct drive axial flux motors are what is used to win those solar car races, being over 97% efficient. Not only that, but since electric motors only draw as much power as their task requires, there is no compelling reason to keep them small and underpowered like their gasoline driven counterparts. 

This picture shows an entirely different problem. Here the bogie is making a very tight turn, far too tight to take with ordinary rigid bogie designs. Here the turn is being accomplished “skid steer” style with the middle guide wheel keeping everything centered. This is would be extremely wearing, but for the slow velocity involved. 

This picture illustrates the problems with tight radius vertical turns. The height of the bogie, relative to the internal structure of the track, changes completely, being too loose in one case and too tight in the other.  Luckily this is not quite as difficult to work with as one might think. During assembly, a collapsible fixture is dimensioned to match the desired internal spacing. The precut and bent steel is clamped to this for welding. Oddly shaped and unwieldy pieces are routinely clamped for welding anyway. Like I said, there’s no reason why the track has to be uniformly dimensioned.

This little design exercise is obviously about more than speed. It is about having mobility capabilities that are closer to a personal helicopter than anything else. It is my belief that such capabilities are not that complicated or expensive. I also believe that integrating PRT infrastructure into an existing (mainly privately owned) cityscape is enough of a challenge to warrant exploring these solutions sooner, rather than later. So, if anyone calls, tell them I’m in the garage – workin’ on the hot rod!

In Search of a Parking Space

The project in Amritsar has underlined some issues about PRT station design that would seem to merit a second look. The system under construction will have seven stations, and 200 vehicles. That comes to 28.6 vehicles per station.  The question, then, is, “Where do the vehicles go when not in use?” The illustration above should give pause. The structure and land use is huge, as are the number of bays, and even this is not enough to house a seventh of the vehicles. Note that there is no parking shown. How do the people get here? More importantly, where do cities get that kind of real estate and how much does it bump up system cost? Here are a few observations:

One of the classic features of PRT design is the off-line station, where empty vehicles wait to take passengers on their way. In the straight-line model favored by Dr. Edward Anderson (now embodied by ITNS, Skyweb Express, Skytran and others) the vehicles wait single-file, similar to a line of taxis. There is none of the inefficiency of backing up, but this advantage must be weighed against the fact that all departing vehicles must wait for the leading vehicle. The greater problem with this serial approach is that it is ill-suited for vehicle storage, as Amritsar exemplifies. For example, if a final occupied vehicle comes into a station that already has 28 empty vehicles in a line, the station would have to be 29 vehicles long to receive it. In the illustration below it can be seen that the tailing vehicle’s passengers cannot get out if there are no outbound passengers.

 

Two solutions come to mind for such systems. One is to simply have a storage facility. As usage declines vehicles would simply take themselves out of the system. The other is to separate the stations into two halves. There would be arriving and departing sections, separated by enough track to store the vehicles. Then, in the case of the last illustration, this could be the loading station only, with all waiting/stored vehicles already emptied. These are both simple enough solutions, but they involve significant system changes.

The saw-tooth parking approach embraced by ULTra, Mister and others, where the vehicles back out, can, in theory, be quite compact, at least in terms of fitting in normal rectangular building lots. Vehicles that are designed to be front loading can be arranged in a typical perpendicular parking configuration and spaced so close together as to be almost touching. This density would be limited only by turning radius and the dynamics of pedestrian movement in the boarding area.

The preferred embodiment may depend on what shape of space is available. For example, the very long, narrow space required for “straight-line” stations might frequently be readily available within existing easements. If it is not, however, and land needs to be procured, the straight line design might prove highly impractical. To further complicate matters there is the matter of visual impact. It might be that the stations or stored vehicles would be considered obtrusive.  

A couple of additional observations: Maintenance and/or recharging might be a factor to consider, as these activities might take vehicles out of service anyway, so some percentage of the fleet would have this additional place to be at night. Also, one interesting idea would be to simply lease office space and store vehicles in a office building or retail space. The space could even double as a private station for tenants. (They probably wouldn’t welcome the extra pedestrians of a public station) Another thought involves open automobile parking. Two of Amritsar’s stations are parking areas, and this may well prove typical. Could automobile parking and “pod” parking be the same? After all, it is after the auto traffic thins out that the PRT vehicles would be most needing spots. In the morning, when the cars roll in, the pods would be there waiting. Alternatively, PRT storage/station could be on the roof over covered parking, something the ULTra illustration would have probably included but for the promotional nature of the rendition.

My own view is that it is important to be as flexible as possible. That means, from a vehicle/track design standpoint, very tight turning radii both vertically and horizontally and very steep slope capability. This enables many configurations for both boarding and storage which are impossible otherwise, such as tightly packed three-dimensional storage arrays. A pod’s door placement is also an extremely important detail that I am still wrestling with. (In post 116 I designed several variations of the in-line type stations which utilize parallel, double-sided boarding, and require left and right side doors, although I have also played with front boarding designs)  

My suspicion is that, upon reviewing actual potential routes and station locations, city planners will generally conclude that these are the challenges that are the hardest and most expensive to conquer.  It does no good to have a system which, by the mile, sounds cheap, but then requires unexpected purchases of real estate, or requires track layouts that prove unacceptable to the communities involved. These are not details but rather the main challenges - The solutions that get weighed against (and can win against) other transit alternatives. The challenge is to have a practical answer for every case, rather than to force a city to search for alternative routes.  If a system won’t work in essentially every instance, it has little chance of ever becoming a pervasive network, and we all know that is where PRT will really shine…if it ever gets that chance.