141> GOT IT!

If you have followed this blog for any length of time, you have witnessed version after version of bogies and track. I started this blog with the naïve hope that I could recruit a bunch of mechanical engineers to create an open source PRT design. Such a consensual design would have had a credibility that was especially lacking back in those dark days before Heathrow and Masdar. Well, lacking the participation I had hoped for, progress has been pretty slow, although, in my own defense, I’ve set the bar pretty high, not just in terms of performance capabilities, but in terms of simplicity, cost and practicality. That’s a bit like trying to mix oil and water.

Anyway, folks, get out the Champaign and the party hats, because I am pretty sure the search is basically over, although I’m still studying tight-quarters switching, and a few other details. Let me reiterate, for new readers, what differentiates these designs. The challenge is to go faster, climb steeper, turn tighter, be less expensive, and therefore be more versatile and practical than other transportation alternatives. I seek a fully 3D solution instead of a system that requires raised stations or long ramps. The pictures here show only the bare essentials. Most structure, including the passenger compartment and the track’s support means have been left out for clarity. 

Here are the highlights of the changes. First, I have replaced the round running guides (A) with square tubing tilted to make a diamond profile. This is almost as easy to bend as round pipe, but offers flat running surfaces that won’t wear grooves into the guide wheels. I have inverted the drive wheel flanges (B) to be convex instead of concave. This results in a single point of angular contact that will be very prone to wear, but for the fact is that these flanges only need to come into contact for specific, short term duties, most of them at very low speeds. For switching they are employed for only a few dozen revolutions. The steering guide wheels (C) and what were called “hold-down” wheels in previous iterations have been combined. Now, when ascending or descending very steep or even vertical runs of track, both of these wheels can be raised to serve the hold-down function. The new geometry makes their previous “anti-rock” function unneeded. The running guide wheels (D) and steering guide wheels (C) must now, though, all move independently, instead of in pairs. Here is how switching would generally work in four pictures.

1. The first of the four is the ordinary running configuration. The drive wheel flanges, although close, do not actually make contact, so all wear is on the larger softer, smoother, and quieter hard rubber wheel surfaces.

2. Several steps have taken place here. First, a steering guide wheel is raised. Next the pairs of diamond guides “taper” into a position where contact can be made. (They start spread out.) Meanwhile, the drive wheel guides make contact with the plastic wheel flanges. This will probably be accomplished by raising the guide wheel slightly on the side that isn’t being lowered. This will pull the bogie out of center, clamping the track between the flange and the guide wheel.  

3. With the prior steps taken, the track sides can begin to diverge. Note that one side of the bogie can now be unsupported. This solves the situation often referred to as the “frog problem.” (The “frog” is the little piece of track that, in suspended designs, has no means of support.)

4. The fourth pic shows the resumption of support under both sides of the bogie. Any “frog” would be cantilevered from this point, as the thin wall separating the two tracks is the only means of its support. At this point, the top guides can be discontinued and the drive wheel flanges can cease contact, to stop wear. From here the tracks can diverge into their respective directions. I have included a couple of additional screenshots, below. As for me, well, you’ll find me throwing out a couple of years’ worth of now obsolete designs. Oh, sweet victory!  

140> Piping Hot Ideas

 

Recently I was reminded by one reader just how many posts I have written, and just how difficult it is to use this site as a resource. Blogs are just like that. The new builds on, but buries, the old. If you come in late, you just don’t know what is going on. Yes, I (ug!) need to update the table of contents and index… Anyway today I am going to go back to the very foundation of the designs found on all of those back pages, the primary design distinction that tends to define and distinguish one PRT system from another… the track.     

The right track is everything. Think of it like a pipe for moving people. After all, our whole way of life is a study in the progress of learning to pipe goods and services with ever greater efficiency. Look at email vs. treemail! Gas pipelines! And, of course, there is the many mile journey of the water coming out of your garden hose and into your flowerbed.  Back in Roman times, huge structures were erected to transport water because it had to be kept flowing gradually downhill. Once pressurized pipes and pumps were introduced, however, water could, for the first time, be efficiently moved anywhere in any direction. Our street system bears some resemblance to those ancient aqueducts, for reasons that contain elements of the same logic. Our vehicles are optimized for relatively level travel, abrupt turns require slow speeds, and of course, gravity is what keeps everything on track. In fact, it is a little appreciated fact that our city streets generally ARE aqueducts, insofar as they are carefully pitched to carry any rainwater away from homes and buildings, without ponding, to the nearest storm sewer. Conversely, highways, being designed expressly for speed, bear more resemblance to pipes or tubes. They are not referred to as traffic “arteries” for nothing! Unfortunately highways have severe limitations that mean that this analogy can only go so far. They are, frankly, huge. They rely on good weather and gravity and use acres of land for a simple turn. Pipes, on the other hand, can go anywhere – up, down, over and under. Their containment means higher speeds are possible and their compact form disguises the surprisingly high volume that a continuous flow can represent over time.  There are places, in some countries, where the water truck still comes down the street so that people can come out and fill their containers. In rural areas, people still rely on fuel trucks stopping by. In the transit analogy this is like buses or light rail letting off passengers. It’s a cumbersome, stop and go world. Piping is so much better.

Futurists have been playing around with the people-pipe idea forever. Anyone out there old enough to remember the Jetsons? The facts on the ground are, however, that physical pipe for humans isn’t really the most practical way to go. It’s too large, and a main point of piping is to economically extend the reach of a resource into all required areas. So the challenge is, then, to devise a system that can move people as though they are being piped, yet be small and flexible enough to be easily extendable into a large network, the way other ”piped” resources are.

Before going any farther, one interesting point about moving people. Oddly, we have little knowledge of how fast this can actually be done. Those familiar with the designs in these pages know that the PRT vehicles herein are specifically designed to eliminate sideways and front-to-back G-forces. For example, a passenger’s beverage, set down, will not spill, much like a bucket of water tied to a rope can be swung in circles, even up-side-down, without spilling a drop. This is contrary to (and better than) our finest, most advanced vehicles, be they luxury cars or fighter jets. There are, however, unavoidable variations in ordinary, vertically oriented gravity and these can cause discomfort. I recall that when I was a child, elevators would give me that weird feeling in the gut. I’m not sure, but I suspect that, over time, the acceleration/deceleration control in elevators has been greatly improved - carefully calibrated to make the effect almost unnoticeable while getting you to your floor just as fast or faster. In any case, doing this in 3D is a brand new field. Nobody has actually tried moving people from here to there as fast as possible, without making them feel yanked around. I predict that the combination of simulated free-hanging and precisely calibrated acceleration and deceleration will prove to be surprisingly effective in “piping people” comfortably. PRT has historically been assumed to have vehicles all moving at the same speed. It was a matter of control. These days, and even more so in the future, PRT vehicles may be programmed to act more autonomously - to be opportunistic - to go as fast as passenger comfort will allow. After all, that is what would happen in fluid dynamics. The Bernoulli principle applied to transit!

There is a lot more to say on this subject, such as the possible dizzying effect of looking out the windows, but that is for a different post. Let’s get back to designing the “pipe”.    

  

So what is the most minimalistic form factor that can hold a vehicle the way pipe walls hold in liquid? In theory, a simple pair of rails is all that it takes. Anyone who has seen a rollercoaster in action can attest to the fact that two rails can rapidly direct and redirect people through 3D space. (Remember, rollercoasters are purposely designed to throw you around, so I sort of hate to use them as an example) Anyway, though, it shows that two rails will work.

The notion of only two rails is a bit deceptive, however. The fact is that holding those two rails in proper orientation requires the lion’s share of the structure. So in actuality, it really doesn’t matter. Two, three, five rails or more…what matters is the overall weight vs. the span vs. factors like ease of construction and material cost. The big question for track designers becomes the tradeoff between many closely spaced supports vs. fewer, but with more massive and costly beams or trusses instead.

This brings up the question of what people will accept visually. Many current systems create a profound canopy effect, particularly where the track splits off to enter a station. If the system is to be two-way the problem is greater still. This effect weighs against the four-wheels-on-the-bottom paradigm seen on most vehicles. That said, the preferred profile for beams or trusses for making long horizontal spans is tall and narrow, not short and wide.  

But there is one other factor. There is the tradeoff between more vibration and noise but long wheel life, on one hand, and a quieter, smoother ride with less wheel life on the other. An obvious example is wheels made of steel or hard plastic vs. rubber tires. This conflict arises from, and is proportional to, speed. At high enough speeds hard wheels are very loud and soft wheels wear out very quickly, as racing fans well know.  The best remedy is to have larger wheels, which, of course, have more surface area. So this, too, gets weighed into the debate about PRT track profile for any fast, wheeled system.

A few decades ago, PRT pioneer Dr. J. Edward Anderson concluded that the best compromise for his single level, but raised, system was a truss about  waist high and about two thirds of that wide. He would use the structure to enclose and support the rails. I have drawn the same conclusion, as far as general dimensions go. This really is sort of a “Goldilocks” compromise. It gives enough interior space for the larger wheels that high speeds with semisoft wheels require and it encloses any noise anyway. (Not to mention weather-proofing the running surfaces!) It allows spanning lengths sufficient to cross at least six lanes of traffic, (Two lanes, each way, plus a turning lane is a very common city intersection size.) It has close to the ideal proportions of width to height.

I have physically placed similarly sized objects, such as large trash cans at a distance to simulate how big the track would look from the ground, and I am satisfied that these dimensions will be found acceptable almost universally, especially if they can contain otherwise unsightly utility wires and improve street lighting in the process. Also, with a fully 3D system the track can be set as high as need be.

So that, for all you new or occasional readers out there, is a brief explanation of the thinking behind the track that you will see on these pages. What I propose is essentially a bogie within a slotted tube that pulls along a vehicle in such a way as to whisk people from anywhere to anywhere faster but more comfortably than any of us have so far experienced. In full 3D. It would, of course, have all of the system traffic management normally associated with PRT and enjoy the benefits of in-vehicle, rather than track-based switching. The bogies use wheels that turn themselves without any additional moving parts and so are exceedingly efficient, especially since they use track-supplied electricity. Oh, and one other thing… It’s fast. It’ll take you from here to there in no time…without snapping your head around!  

139> 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!)  

138> 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. 

137> 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!

136> 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!

135> 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.

134> Good Tidings!

Well, as 2011 draws to a close, we PRT believers have been given a Christmas present!  Finally, for the first time in history, a large city with a real traffic problem is actually going to install a meaningful PRT system.  ULTra, having proved its technology in its Heathrow Airport system, has partnered with an Indian company to build a 200 vehicle, 100k passenger per day system in Amritsar, India.

I know.  I’ve been critical of ULTra in past posts.  I have questioned if the system really can be called PRT at all – if coordinated robocars really fit the definition, especially since they do not enjoy the weatherproof speed and efficiency advantages of running on steel rails.  I have worried aloud if the inherent performance shortcomings of steerable soft rubber tires on “pavement” would give PRT a bad name.  But I have to say, all in all, that I’m pretty damned pleased, and I’ll tell you why.

There is one basic concept, best taught through demonstration that can promote PRT globally.  It is the fact that, in an urban setting, ONLY multi-level transportation can be non-stop, and only non-stop travel makes sense in an increasingly resource-strapped world.  Since multi-level roadways are too expensive and massive to deploy en masse, the most straight-forward approach is to create a new, lighter infrastructure that can be more affordably elevated above interfering traffic.  This lighter infrastructure requires lighter vehicles and payloads as well.  The logical way to speed throughput on this smaller infrastructure is intelligent automation - the combination we call Personal Rapid Transit.  I had previously worried that a system like ULTra would end up, for cost reasons, having a great deal of track on the ground, which essentially misses the point.  It appears that this is not the case.

It also appears that this venture is designed to make a profit for shareholders, with affordable fares, no less.  This is obviously a huge deal, especially since every other option ends up being supported with tax dollars.  I wish I knew more of the financing details…It sounds almost too good to be true.

We humans are far better at perfecting things than inventing them from scratch, so even if the world comes to believe that the ULTra design is the very definition of PRT, it won’t be long before more capable versions begin to appear.  Undoubtedly such work is being done by ULTra itself.

What we will see in Amritsar is not at all what the early PRT pioneers had in mind.  There are no grids of one-way track with small, evenly spaced stations.  There is no attempt at blanket coverage.  There are no loops; these guideways will be bi-directional.  The route appears to have a combination of straight runs and a few fairly sharp turns, a combination that will slow fixed speed systems to the speed of the sharpest turn.  Unlike the utopian notion of a car free city, many passengers will park their cars and take the system from there.  There were the predictable protests over the track, although given the climate; I would wager that those shopkeepers will learn to appreciate every bit of shade afforded by the canopy.

The plan calls for connecting seven destinations:  The bus station, the train station, two parking lots, a school (chosen because it was non-private land next to a large commercial complex?) a Bazaar, and a major tourist attraction, the “Golden Temple.”  These people need more roads where there is no space for roads, more parking where there is no space for that either.  There was little choice as to the routing.  What you are handed is you get to work with. Sound like anywhere you know?

The fact remains that we really don’t know how the Amritsar system would compare to the same elevated track populated by ordinary motorized rickshaws, a similarly sized, common form of transportation in that part of the world.  This case, however, bears little resemblance to the 1.2 vehicle occupants we are used to.  They are reportedly going to pack in up to 6 per vehicle, so any driver would represent reduced capacity.  What we do know is that, even though most people’s eyes glaze over when you start talking about a whole new infrastructure, some developers and some people in the Punjab government “got it,” and took a leap of faith.  This is a very, very good thing.  The more successful it is, the more it will attract competition and innovation.

There are a number of lessons here for PRT designers and would-be PRT vendors.  One is to get big local partners.  Who can dispute, for example, the (often greedy) symbiosis between real-estate development, politics and infrastructure?  ULTra’s Indian partner, Fairwood Consultants, boasts 25 billion in projects under management.  That opens a lot of doors.

A related issue is core competency.  Ultra has never really tried to break much new ground, mechanically speaking.  They use pretty conventional electric vehicles on a track that is nothing special either.  They didn’t even opt for advanced batteries, but use simple lead acid ones (like a golf cart) instead.  But this is not really a liability.  Instead of expending energy working the bugs out of a bunch of new, experimental subsystems, they get to concentrate on creating traffic solutions with what they have.  Eventually some company, with deep pockets and great mechanical engineering expertise, will see building a more advanced system as a venture with little downside risk, so long as they themselves are partnered with a company with a proven track record of implementing such systems.  ULTra, by this point, will presumably have further cemented its leadership position in that role.

I think they had better not wait too long before they get such a partner however.  If their system in Amritsar proves successful and they land subsequent deals, there will be imitators and competitors coming out of the woodwork.  My own design explorations have convinced me that there are huge performance improvements to be had across the board, as measured by essentially every important metric.  But their success can only make such a partner easier to find.  I believe that there is huge amount of positive PR to be gained by any company that takes this plunge.  They would be seen as agents of change, as green, and as technological leaders, saviors of the taxpayer, solvers of government debt and on and on…  Again, if ULTra can handle the “behind the scenes” grunt work involved in landing deals, planning routes, working with local partners, and generally handling the logistics,(and/or operations)  they will become the indispensable (although less glamorous) part of what could become a very big and profitable industry.  Wouldn’t it be interesting if a future headline read, “Airbus Industrie Partners with ULTra Global to Create Next Generation Pod-Cars?” Or how about Honda?  Or Embraer? Or Bombardier? Or even GM?  

So, on this special day, I tip my hat to the folks at ULTra.  Well Done.  Yes, my friends, we have good tidings!  And a Merry Christmas to all of you!

133> Maglev Mania

Recently there was a posting in the Transport Innovators site that caught my eye.  It was entitled “SkyTran a Sham?” I know… I really should join that group and post my thoughts on that site, and lend a little support to what I consider to be a valuable public resource.  But I like to scratch my head and measure my words a bit more than most before I open up my mouth, and I am usually too busy to even consider an issue on a timely basis anyway.  So I hoard my musings away, like precious little nuggets, to be used as rainy day subject matter for this blog.

I am not so interested in the charge that was made against SkyTran but rather by whom it was made.  It was leveled by the author of this study, which starts out promoting and then later disparaging nearly the exact same concepts as SkyTran.  In my opinion both have severe problems.  The author threw in the towel.  SkyTran still purports to be a practical system.

What is it about maglev that makes smart people so crazy as to think that it is appropriate for PRT? maglev’s major advantage is being frictionless, except for air.  This is a very minor consideration at city speeds, and yet they want to shoehorn this high speed technology into the sharp cornered, stop and go world of urban transit.  A friction free object wants to glide at a steady speed, in a straight line.  Navigating a city requires something wholly different.  Both systems are designed to travel in excess of 200 km/h (124 mph), far too fast for short trips.  Even though he states that, because of G-force constraints, average system speed can never exceed 100km/h (62 mph) in an urban environment, he never wavers from his 200 km/h maglev design, and the inflated track cost that it entails.   

In the case of Swift PRT, the author, after all kinds of analysis and simulations, concludes that the track is too expensive (Duh! It’s full of copper coils!) and that vehicles that fast must be spaced way apart to allow exiting, entering, or even simple turns.  (Or, alternatively, they need 600 meter ramps to and from the stations.)  He states, “If your intersection or station spacing is meant to be <1km apart, you effectively need two lanes in each direction:  a fast lane, and an acceleration/deceleration lane.  The net result is you have at least doubled your track costs, and the width of your system.” It seems to me that the problem lies with trying to connect 200 km/h fast lanes to every downtown station!  That seems to be what SkyTran is advocating as well.  Like I say, there seems to be something about maglev that makes people lose their senses.

The conclusions are what bother me most:  While I have no problem with his realization that maglev PRT is not cost effective, he then applies his figures to PRT generally.  His assumption is that all PRT track must cost 7m/km, even though his own figures show that one way track without the copper coils and in-track electronics would come in at 2m/km.  He then, through mathematical inference, extends this inflated cost to justify only putting one station per 2.7 km, and then uses this spacing to assert that PRT (in general) cannot compete because of the long walks to get to the station.  His reliance on formulas over common sense has led to the “crap-in, crap-out” phenomena.

What is curious (and unfortunate) is the illogical leap from discovering that his system is too fast and expensive to the conclusion that the future of transportation is in vehicles that run on asphalt.  This argument is made without anything to back it up, save the cost and ubiquity of the road system itself. Was it not the shortcomings of the road system that lead him to explore PRT in the first place?  Sure, I think we all agree that traffic problems can be reduced by using networking and AI technologies.  But asphalt will always be primarily a two dimensional, stop and go system.  Multilevel interchanges simply cost too much and are too big to be ubiquitous.  So when he compares the cost of his 130 mph, non-stop system against asphalt, he is comparing apples and oranges.  If I had to venture a guess, I would say that the author set up an experiment that he was forced to carry it out with scientific rigor, even though the basis for the experiment (his hypothetical system) was clearly flawed.  Having exhausted his time and/or interest, he was in no mood to do it all over with a better system, and so hastily framed his results.  These conclusions certainly do not reflect the thoughtfulness shown in the sections where he first discusses the original problem.

That being said, one other interesting result of the study highlights the parking problem, something that is often glossed over in PRT discussions.  While it has been admitted that PRT vehicles will have to travel around empty sometimes, the extent to which this will occur has been a subject that has remained somewhat opaque.  Obviously, during off-hours, if the system is only operating at half capacity, there are 50% empty vehicles, and they have to be somewhere.  Are they traveling around in circles?  Clearly these vehicles should be staged somewhere, but I have not seen this reality reflected in the various PRT designs.  It occurs to me that this is still one more argument for a fully multi-axis (3D) system.  Warehousing numbers of empty vehicles would be much more space-efficient if they don’t require long ramps.  As with parking cars, a vehicle with a small turning radius is a plus.  In PRT, such a radius might be horizontal or vertical.  Compact parking is especially important if an attempt is going to be made to shelter those vehicles from the elements.  A PRT design that allows a combination of tight turns and compact track switching in full 3D can clearly minimize the real estate (and roofing) required for such storage.  Being able to make multiple track configurations in tight spaces would be particularly advantageous in utilizing whatever real estate might be available, including very small or oddly shaped lots.  Such parking can be envisioned more in terms of a lattice or matrix, as compared to lines of cars on  long parallel tracks typified by the storage of railroad cars.

I might add that tight turning radii in both vertical and horizontal axes is inherently difficult to achieve in systems that use the track as part of the propulsion. This is because of the required tight spacing between track and bogie. Magnetism loses force with distance, so using magnetism between track and bogie for propulsion will always entail a fairly tight fit. This is my major beef with linear motor propulsion, even non-maglev varieties such as simple LIMs, which don’t require coils in the track.   

Anyway, to those of us not under the maglev spell, this study illustrates some of the challenges of PRT design that must be, and, indeed, can be properly addressed.  The challenge of G forces, of storing and staging pods, the track cost issues, the station spacing… All of these must be carefully balanced and tweaked if PRT is to succeed without the blunt instrument of generous government subsidies.  Any good PRT design must address these issues from the onset, not as afterthoughts.  Otherwise it will either fail outright or be relegated to a few niche markets.

132> Forward Compatibility

I know I said that my next post would be about standards, but I think this topic should come first since it weighs into that discussion. There has been something in the back of my mind, in every design that I have posted on this blog. It is the recognition that progress often happens in baby steps, yet baby steps often don’t go in a straight line or a logical direction.  

I am talking about forward compatibility. The vexing thing about designing PRT (or anything else) to be forward compatible is that it requires a design that allows evolution toward an end that must first be defined itself. In the case of PRT, that eventual product would ideally be very fast, silent, comfortable, able to be deployed with minimal cost, and be adaptable for every contingency a city could throw at it. These adaptions  would include a variety of station types for different locations and passenger volumes, being practical within buildings, being able to be elevated to a level deemed acceptable by the effected parties, etc. The vehicles themselves can be assumed to be, in this future world, mass produced to point of enjoying economies of scale.

I am sure that many readers have dismissed my designs as being too ambitious. The vehicles, in particular, have very advanced electro-mechanical systems which are designed to remedy situations which could largely be avoided in the first place with little negative impact. Well now you know the reason. By designing the vehicles as though Toyota had been building them for decades, one can better consider the best design for the track and stations that may still be around when that day comes.

In the meantime, however, PRT will be subject to the restrictions that our current economic, political and technological realities place on it. The problem is that designs for today and designs for tomorrow are strikingly different. The main culprit is the tire wear and noise/vibration associated with speed. It is true that smooth running surfaces and track clamping emergency braking capability enable harder rubber, solid tires which don’t need to flatten out on pavement to achieve the high traction requirements associated with gripping slippery roads. Still, highly wear resistant plastics, such as are seen in rollercoaster wheels, are a recipe for a very noisy system at high speeds, especially on pipe, which is notoriously good at amplifying sound. (This is the basis for many musical instruments)

I should point out that the design I show in the Oct. 30 post enables both steering guide wheels to be raised for high speeds, eliminating contact (and therefore noise and wear) by the plastic flanges. Also, these flanges are to rotate independently of the drive wheels, so that they may make contact with the track (pipe) anywhere on their surface and create their own rotational speed based on the diameter established by that point, rather than the smaller diameter of the tire. This reduces wear on what is a tiny contact point.

The main point remains, however, that high speed systems should have larger wheels (OK, not Maglev) or risk lots of wear and/or lots of noise. A system that requires wheels or tires to be changed every few thousand miles would be a disaster. But longer wearing, larger tires means bigger track, something that is nearly as bad, in that it raises the cost and visual impact of a system which will, in the beginning, be under intense scrutiny from critics. Also initial systems will probably be slower anyway, because such trial systems will have to first prove themselves for short-distance downtown use. 

Could there be a two tier system? Would it be crazy to start with a system for downtown that would preclude high speed vehicles? I know it sounds like a terrible idea, but it would probably shave 20% off of the track costs, and vehicles would be discounted considerably more. And let’s face it. The other PRT systems out there aren’t exactly fast or flexible either.

In the illustration above, the system on the left, which is obviously simplistic and incomplete, would only need to raise and lower the small pairs of wheels to steer. I do not believe that the middle “hold-down” wheels (illustrated in previous posts) would be required, so that’s really all there is. There are inexpensive “off the shelf” hub motors available that would fit in the drive wheels, and the flange and hubs could be cast as one, (in urethane) so that solid rubber tires would slip on. Such a bogie would be extremely cheap to produce. The complex (expensive) articulation capabilities of the swing-arm and gondola could also be dialed back in such a “starter” system.  

The obvious problem comes from the fact that the fast vehicles wouldn’t fit in the smaller track, although the slow vehicles could run in the high speed track. So what is a city to do? Well, there are a couple of things to note here. First, the high speed track would be equally usable for GRT. (Group Rapid Transit.)  A track going out to an airport, for example, might well be a good stand-alone investment used in this way. Passengers coming from the airport to downtown would need to change vehicles to use the downtown PRT, but the upside is that they didn’t have to make the long trip at 30 mph.  Faster, express PRT could share the track at some point, and slow vehicles could use the track at certain times of day. Because PRT is a smart technology, if high-speed track is running through a grid of low speed track, the slow vehicles could still, in theory, get on and off without disrupting the high speed service. (Assuming sparse high speed traffic) If the track is modular, standardized and interchangeable, the slow track could be removed (during an upgrade) and be reused elsewhere. In the airport example, for instance, slow track taken from downtown could be used to build a network around that airport. In such a case changing vehicles would be a minor inconvenience for relatively few passengers. It is also noteworthy that, in a downtown environment with mixed track, fast vehicles can’t get up to speed anyway, because of sharp turns. Therefore slow vehicles sharing the (fast) track would be no problem. In such a case the system could simply send a slow vehicle if a trip would involve a stretch of slow track.

I have come to the conclusion, reluctantly, that there are theoretically reasonable migration paths from slower, inexpensive PRT to faster systems capable of tackling longer distance commuter traffic. The examples above are just a sample of the possibilities.  They also show that it takes some creativity to undo what many of us would say is a very shortsighted decision. (To put down track that can’t take fast vehicles)  But at least it’s better than having no forward compatibility at all!  It is unfortunate that such a complicated situation should ever exist in the first place, but I have my doubts that we can ever get to PRT 2.0 without first dabbling in PRT 1.0.