131> Climbing a Chain

Suspended PRT has the advantage (over bottom supported systems) of being well suited for very steep slopes.  As I have pointed out in previous posts, I believe this attribute is essential to achieving flexibility in routing and station placement because it enables a completely three-dimensional transportation solution.  Such flexibility could be important for keeping costs down and increasing ridership.  I do not think that starting with the supposition that each station must handle a minimum of many dozens of passengers per hour gives the kind of flexibility that cities need.  Such pedestrian-rich station locations may not be close enough to each other to make a walkable grid of coverage and getting to such strategically placed stations might well involve more car travel than the PRT trip is likely to save.  This makes dirt-cheap stations very important.  Bare-bones ground level boarding, say, at bus stops, is an option that is out of the question with most supported systems because the ramps would be in the way.

The picture above shows a minimal station in a park. While it clearly is a low throughput design, it also would not require a lot of passengers to pay off.  Small neighborhood parks are very common in the US, often created by the real estate developers to help attract home buyers to a subdivision.  Better still, they are usually located at or near a subdivision’s entrance.  Such small neighborhood stations could exist along a routes that are important but aren’t part of a grid, say from an airport to a downtown area, or between two metropolitan areas that have grown together.  Once residents realize the benefit of such an access point and station’s capacity becomes a problem the station could be upgraded, this time based on real-world ridership numbers.   The foot-in-the-door approach to eco-friendly commuting!

This (more multi-axis) approach should also allow options that will help in the “not-in-my-front-yard!” confrontations that any new transportation infrastructure is sure to create.  For example, it enables the track to be run at a much higher altitude than systems that rely on elevators or gradual ramps.  Instead of a “take it or leave it” approach, there is the option of running the track above the tree tops if necessary.  

None of this, however, is possible without a straight-forward and inexpensive way to engineer this capability into the system.  

Here is such a method.  I have illustrated it with only the relevant wheels and engageable surfaces of the track shown.  The last post shows the track and vehicle in more detail.  (To any newbies to the site out there, I advocate direct-drive “hub motors” which rotate around electrically fed axles, so actually the whole drive system is shown!)  This design is fashioned after the rack and pinion system used by cog railways.  The trick is to make it engageable and disengageable without complicated mechanisms that would drive up costs and reduce reliability.  It uses two stretched lengths of modified roller chain as a rack, and a sprocket that is of much reduced diameter (compared to the wheels) to eliminate the need for a low gear for slow but powerful climbing.  This method adds next to nothing to the costs or complexity of the system.  Such custom links as I use here (and, indeed, whole specialty chains) are widely available because they are commonly used for material handling tasks in industrial production lines.  Here is how it engages, step-by-step.  

The forward wheels move off of the flat running surface, so they are supported by the flanges alone, which rotate separately and freely from the motorized, rubber-clad drive wheels.  For a moment the front wheels can then spin freely as the bogie is being pushed forward by the rear wheels alone.  The motor controller then increases the rotational speed of the front wheels to compensate for the smaller diameter sprocket.  (The front and rear wheels must now be synchronized at two different speeds.)  As the sprocket engages the chain there is near certainty that the teeth will not be in the exact position to mesh exactly.  To adjust for this, there is a compressible rubber cushion (shown in green) which allows the chain to “stretch.”  Additionally, it is possible to design some limited rotational play into the sprocket hub.  Since we are talking about roller chain here, any occasional slipping will not “grind the gears” causing excessive wear as would be the case in a typical rack and pinion.  Keep in mind that this transition is not expected to be taken at anything approaching normal operating speed.  Once the chains mesh with the front sprockets, engagement is kept captive by an upper bar which presses on a freely rotatable ring (blue) mounted on the wheel’s axle.  This pushes the sprocket teeth into the chain and holds them from slipping out.  Although this may seem redundant because the middle, hold-down wheels do the same thing, (push down) I added this component because I was worried that the compression of the rubber tire would allow the sprocket teeth to slip, and I prefer that rubber because of noise and vibration dampening at high speeds.  Anyway, at this point none of the track’s normal wheel support surfaces are necessary for the front wheels to pull or stay centered.  With the front wheels engaged, the rear wheels will follow a similar sequence but without any question about meshing, since the distance between wheels can be precisely set to match the chain.  Of course the whole process can happen in reverse as well, to go from chain back to ordinary track .

Some readers might be concerned that the chain and sprocket are not strong enough to be used in this fashion, especially since normally at least a half a dozen teeth of each sprocket engage a chain. Each sprocket tooth, however, will have a test strength of at least 3500 lbs. The test strength of chains of the size pictured is at least 12,500 lbs. each.

Footnotes… The design as shown is based on four drive wheels, with the hold-down wheels being free-turning. This is a somewhat arbitrary decision. (The hold-down wheels make the system “half-track capable,” meaning the vehicle can travel on the either its left or right wheels alone without possibly twisting inside the track from lack of support – an essential attribute for switching tracks without the tracks themselves having moveable parts.) These hold-down wheels could just as well share propulsion and braking duties, and so could also be configured with additional sprockets and chains themselves.

Finally, A personal opinion:  I think PRT designers should take a page from the late Steve Jobs. A lot of what he did was to take existing ideas and products and redefine them by engineering them so they were a joy to the senses. He had zero tolerance for the slightly funky design choices that help rush products into the marketplace, only to limit their acceptance in the long run.  When I look at the current PRT offerings out there I see such design compromises by the boatload. We, at least in the developed world, will never fully embrace any system that is clunky, bumpy, noisy or slow! We must recognize that the bar has been set very high by a hundred years of automobile engineering and try our best not to disappoint. But then again even a Ferrari can’t rescue you from the congested city streets by going straight up!  

130> Progress Report

As many of you know, I have been advocating the standardization of key PRT technologies in order to allow PRT to be developed, produced and deployed by a consortium, rather than a single company. This, in turn, requires that this development be started on a basis of the most promising design approaches. I have concentrated my efforts on a suspended system, rather than the bottom supported approach, even though I suspect that the majority of readers prefer the latter. One key to why I think suspended systems represent the best way forward is referred to in my latest iteration of the acronym “SMART,” which is what I call this effort.  (“Standardized Multi-axis Automated Rail Transport”)  

As I have pointed out numerous times before, all “ground” transportation suffers from the same problem: Vehicles or people going in different directions will run into each other unless they stop and wait their turn. Going over or under solves this problem, but that solution is too expensive to deploy universally with current modes of transportation. That indispensable artery of modern commerce, the freeway, clearly shows how effective high-speed non-stop transportation can be. This is simply the result of what happens when a transportation system is modified to be multi-axis instead of existing on one plane - the ground. Unfortunately making multi-level (multi-axis) routing for large vehicles such as trucks and trains takes huge amounts of money and space. When it comes to multi-axis transport, smaller is better. Luckily, we mortals are pretty small.

A multi-axis automated rail transportation system is essentially a new infrastructure designed to do what the freeway can’t. Go to any street, to any bus stop, to any building. It would be designed to be faster and safer than driving, more energy efficient than the most advanced electric car, and expandable for a fraction of the cost of roads. Being natively multi-axis, a suspended system can be employed in areas where long ramps are undesirable (that’s basically everywhere) and the system can be elevated higher than would be practical for supported systems. This can minimize visual impact. While it is true that a supported vehicle can be made to self-bank and keep its cabin level on slopes, it is much more cumbersome to engineer. Vehicles with wheels on the bottom are just ill-suited for extremely steep travel, while hanging vehicles have no such problem. Traditional PRT designs require raised, elevator equipped stations because otherwise the entrance and exit ramps into the station would block driveways, be subject to climbing, and be visually intrusive. A native 3D system has no such restrictions. A suspended vehicle can either taxi in like an airplane or come down like a helicopter. This means that stations can be put nearly anywhere, and they can be very minimal and inexpensive. They do not require high traffic volume to pay for themselves, so they may be placed with high frequency, like bus stops rather than actual stations.  This will increase ridership. The question is this: If we are going to build a whole new infrastructure, do we want it to be raised, single-level, multilevel with ramps, or natively  multi-axis? A consideration of the various routing situations likely to be encountered in a widely deployed system leads me to believe that it would be better to have true multi-axis capabilities from the start.  Anyway, here is the latest iteration of the SMART PRT vehicle concept. Hmm… How about “SMARTPOD?”….Sorta has a ring to it…

Unlike previous versions, the steering guide wheels have been moved outside and under the track. This shaves off about five inches from the track height, bringing it down to about  30 inches/76 cm. (less if it the track is hung from a ceiling.) What is shown here is a high-speed vehicle, (highway speeds and higher) designed for many tens of thousands of miles between tire changes. (hence the large wheels)

The wheel flanges are designed to outlast the tires in two ways. They turn independently of the wheels, so if they contact the track at a different diameter than the tires there will be no conflict. Secondly, they are only deployed during actual turns. Otherwise the bogey is centered by leaving both left and right steering guide wheels in the upright position. The upper “hold-down” wheels replace the upper steering guide wheels of previous designs, prohibiting any rotation of the bogey within the track. This design is extremely maneuverable with a turning radius of a mere 8 ft., including vertical turns. (The spacing between various track surfaces must vary, however.) The pictured design is missing most of the components of the bogie at this stage of development. The sprockets pictured are for vertical climbing, although I plan to adjust the sprocket size somewhat.  

The track has been designed to be extremely easy to fabricate into sections that are straight or curved. There would be no problem finding shops willing to bid this work, even in small towns if the pipe bending is outsourced.  Removal of a left or right truss section will not mean that vehicles cannot pass, although there is a small temporary rail that needs to be placed as insurance against any freak events that would make the whole vehicle sway with great force. I am still working the best way to attach sheathing, although the reader will note that there is a slight arc to the outer edges of the truss. This is to make light-weight metal or plastic sheathing more rigid.

Alert readers will notice an air scoop. At this point I am leaning toward liquid cooled motors. This greatly increases the performance-to-weight characteristics of the motors, and hub motors are ideally suited for this, as the copper coils that need cooling are stationary and accessible radially from where the wheel attaches to the frame. A simple little electric pump that is remote from the motor itself is all that is needed. No moving parts are added to the motor. The scoop is for a radiator/heat exchanger.

Finally, I want to emphasize that this vehicle has capabilities that go well beyond what is likely to be deployed early on. Nonetheless, I am designing with the future in mind so aspects that are practical today but foreclose later improvement can be avoided. Water cooling, high speeds and vertical climbing are features that might be expensive complications to first deployments. However I see little point in building an infrastructure project whose inherent design limitations will become apparent as soon as it is deemed a success.  This is, in part, why I favor a full multi-axis approach. Future cities are only going to get more crowded and time is only going to get more precious.   

129> Emergency!

Do a PRT vehicles need a way to for people to escape in an emergency?  Many seem to think so, in that I am aware of a number of systems that have stated evacuation procedures.  This is problem of elevated track, since obviously if the vehicle is on the ground one can just get out, so long as the doors can open.  It is particularly difficult with suspended vehicles or systems that employ track that is too narrow to walk on.  This is unfortunate, because the very real advantage of being minimal and out of the way becomes a disadvantage in this case.

All of this begs the question of what can stop a PRT system in the first place.  The historically contemplated mode of failure is some sort of systemic computer problem.  In a system with completely centralized control, a system outage would stop all traffic.  Yet Google and others have demonstrated autonomously piloted automobiles.  If all PRT vehicles can be sufficiently autonomous to find their way to a station, then that would seem to rule that problem out.  Advances in battery technology have made it much easier to have ample on-board backup power to get to a station, so a systemic power failure wouldn’t seem to pose a problem either.

Then there is the in-vehicle failure.  It should be noted that two such failures could trap all vehicles between the two and that a single such failure requires that all vehicles must be able to operate in reverse.

With a direct drive (hub motor) system, like I advocate, mechanical failure is exceedingly unlikely.  After all, the only moving part is the wheel itself, so there is no drive train to break down. Each wheel turns on its own.  In-vehicle control or communications failure?  It would seem that there are a number of remedies for these possibilities as well, the most obvious being a redundant backup system.  After all, the cost of computer boards these days is hardly worth mentioning.   I suppose a last resort would be to pulse the motors very slowly (this will make them incrementally turn a few degrees with each pulse) without the computer systems.  The steering guides would be set to exit at the next ramp, and the vehicle would emit a beacon to alert other vehicles.  All of this could be triggered with simple relays or even manually. Furthermore, at least in the designs I am contemplating, the vehicles’ bogies, which are located inside the track, have bumper/coupling means.  They can both push and pull other vehicles.

Then there is the possibility of a break in the track, say from an earthquake or large truck collision.  This is a psychological barrier as much as an actual threat, in that the idea of flying off a broken track into free fall is a particularly frightening vision.  With good brakes and the right software, it seems like thus too should be manageable, unless there are multiple breaks in the track, cutting off whole sections from a station.  Such a case, it should be mentioned, would foil almost all evacuation plans, even if the vehicles were riding atop a wide causeway, unless it is one with very frequent exit stairs.  I might  mention here the break detection system employed by Disney for their rollercoasters:  The pipes that comprise the track are filled with compressed gas. A reduction in pressure means that there might be a break.   I would also add that with a hanging system, one of the advantages is that stations do not require lengthy ramps or elevated stations.  This would favor stations being positioned with more frequency, reducing the number of potentially stranded passengers. 

                                                                                                                                                                  

Then there is fire. With the motors being separated from the vehicle as they are in a suspended system,

even if there were a large amount of flammable materials in the motor, (which there aren’t) there

is still no way it could catch the cabin on fire. What about the cabin itself? This presents the one tricky

problem.  How do you stop some idiot with boxes of papers and a lighter from starting his own fire? One obvious, but partial, remedy is to have a smoke detection system which automatically sends the vehicle to the next stop.  I suppose that there is also the possibility of some release of noxious fumes from a power supply or other computer component overheating or burning out. The fact that computers are ever-shrinking and

requiring less and less power seems to indicate that this won’t be a problem. I suppose, also, that it possible that a passenger might spill a bottle of ammonia or puncture an aerosol can. The need for emergency outside air seems far-fetched, but is worth at least considering when weighing design options. 

So it seems like a catastrophic earthquake, multiple separate vehicle failures, or a very foolish passenger are the main causes that would require evacuation, so long as the vehicles are at least semi-autonomous and have robust back-up power. That and simple human psychology. Perhaps there needs to be a way to evacuate passengers simply to make the system more saleable. After all, the fire and police departments might see this as just another potential drain on resources. And of course there is the law. Perhaps some well-meaning politician has put “public safety first” and created a legal hurdle. If there is such a statute, I am not aware of it, but of course this would vary between countries. 

If there absolutely must be an evacuation means, for a hanging system I can see a few possibilities.

One is to have some sort of extra rail all along the track where emergency vehicles could travel, unimpeded by stalled vehicles, getting access to all.  This is cumbersome to engineer well, but is at least worth contemplating.

Another solution is to have a means to lower the cabin or parts of it. This could be done with a very small winch, since it doesn’t need to raise the cabin fully loaded or be in any particular hurry. With gravity assisting, cables could be lowered with the most minimal of motors, or even by gravity alone. The tricky part is how far such a system could or should go before wind starts becoming a factor. Even with telescoping scissor-action stabilizers, diagonal cabling and every other means, there is still a problem if you go high enough. There is also the matter of limited choice as to what is below. Is the terrain level? Is it the middle of a highway?  In the end Bubbles and Beams video, the vehicle leaves the system via an elevator of sorts, which is little more than a pole and some cables. The arrangement looks a bit flimsy, at least for going up and down on a regular basis. Going down in an emergency, however, is a whole different matter. Perhaps such poles could be placed periodically or some of the support poles themselves could be so equipped.

A variation on that theme is something I am currently working on. It would involve a fold-out platform or seat which the track support poles could be fitted with. This could be lowered via a cable running inside of a channel.

I can also envision such cable-inside-of-a-channel lowering means that can be mounted to the underside of the track, so they could swing down.  Even rudimentary (very narrow) ladders could swing down in this way. 

This all then brings up to more questions:  How often along a track would escape equipment be appropriate?  If money were absolutely no object, there is no end to the clever things that could be miraculously folded into the track.  There is also the matter of the equality of escape means.  If there were ladders integrated into the support poles where would that leave the elderly or disabled?  Where do you draw the line between stairs and ladders and ramps?

If this all seems a bit extreme to you, join the club. I really think that having some control autonomy with onboard backup power is enough, but I may suffer less acrophobia/claustrophobia than most.  Still it needs to be figured out. If there is a “safety” feature that can packed into the package, can you imagine any elected official NOT electing to include it?  Or can you imagine anyone buying a system in which such matters haven’t been adequately addressed?

Finally, a note to my readers. Lately I have been designing more and blogging less.  Originally I had hoped that with enough readers, I might get some help in the design work.  It appears that isn’t going to be the case, so I will no longer chase readership with frequent posts.  This blog was never about entertainment, after all. As designs progress, they become more difficult to explain.  There is huge difference (in the amount of time involved) between an “artist’s conception” and something that can actually be built.  I am a guy who builds things, so I am not content to just leave things at that early stage of development. This does not mean I won’t ever post opinion or general interest stuff. I will when something comes to me.  Better to have quality than quantity, if readership numbers are not the object. Currently I am in the middle of a whole new bogie and track design, something which I have worked on almost daily. These things take lots of time!

128> Learning from Roller Coaster Design

 

I have previously written about how we need a three dimensional approach to transportation, and one of the main themes I have returned to, design-wise, is of a PRT system that can be routed with minimum of restrictions – a track that can go up or down steeply or around curves tightly, coupled with a vehicle to match. 

It is very tempting to model raised track after bridges.  After all, in most cases, that is essentially what we’re dealing with.  But bridges, as we know them, weren’t really designed for the task at hand. Bridges for ordinary vehicles are necessarily gradual in any curvature because vehicles are generally heavy, and so have great momentum, or are not running on tracks, so they may skid off course.  With a vehicle that is both light and locked onto rails, turning radius or elevation changes can be taken at speeds that are as fast as passenger comfort will allow.  In the past, it was necessary to keep all vehicles going at a single, constant speed.  At least from a computer/control standpoint, that is no longer the case.  If there’s a place where only a hairpin turn will work, the entire system need not be held hostage to the speed for that turn.  In the case of empty vehicles, it makes little sense to run the vehicles unnecessarily.  Garaging the vehicles in shaded (or even climate controlled) storage locations could be advantageous, but would be particularly so if its feeder track, from where it diverges to where it rejoins, is as compact as possible.  Staging, garaging, and repairing vehicles takes space, and space is expensive.  I have seen little in current PRT designs that acknowledges this reality.  As a matter of fact, little attention has been paid to the amount of track involved in acceleration/deceleration lanes for stations.  Perhaps this is because the systems have traditionally been designed to be slow.  Unfortunately, going even reasonably fast opens a whole can of worms, design-wise.  But a really smooth, quiet and fast ride is what will make believers out of the passengers.  A slow, clunky implementation is what will ensure that PRT doesn’t catch on.    

                                                                      

Here are some thoughts regarding actual construction of track:  First of all, the track will no doubt be made in sections in a fabrication shop and trucked to the site, where it must fit together. Any on-site welding, if any, will be minimal, especially considering that expansion joints will be required between sections or groups of sections. Steel can expand nearly an inch per hundred feet between record temperature lows and highs for many areas. 

Although it is possible to bend any shape of structural steel, pipe is by far the least troublesome, at least when it comes to complex curves, where the steel must bend, at once, both up or down and sideways.  Squared stock, having a top and bottom that should remain level and sides that should remain plumb, presents a challenge that does not exist with round pipe.  Squared profiles can be produced with precision from welded flat stock however, although that is a lot of welding.  Pipe joints can easily accommodate expansion with a tightly fit inner sleeve that is only welded on one side.  The outer, running surfaces can be angle-cut or even finger-jointed to ensure a smooth ride.   

Presumably track would be assembled on some sort of scaffolding – a big jig that would establish the endpoints and angles while supporting the pieces for welding.  Pipe bending is an imprecise business, as there is some tendency for steel to spring back. Requiring radii of absolute precision is a recipe for very high costs, so any design should accommodate this fact. 

Luckily, such challenges have been faced before by the makers of roller coasters, and I think that their design conclusions apply here as well.  In the top picture, it appears that the large pipe may actually be many segments of straight pipe with only the small pipe being actually bent, although we can’t be sure.  That certainly is a possibility for eliminating some bending altogether. Note the periodic bolted flanges. This universal connection scheme greatly simplifies assembly in the field. I have looked for, but not found, expansion joints.  I believe this is because the loops and curves can enlarge in terms of radius, eliminating the need.  This system is clearly not as strong as it would be with the same weight of steel used in a triangulated truss design, but the simplicity of fabrication more than makes up for it.  Actually, triangulated trusses are not unheard of in roller coasters, as my Google image search revealed, but I think the point here is that with sufficient support they can be removed.  Consider, for example, the track as it approaches the docking area.  Depending on the situation, the track might curve in complex ways, while supports might be quite closely spaced.  Here you would need no triangulating trusses, and, indeed, they would be all different lengths and an unnecessary complication.  A straight run over a highway, on the other hand, would call for a stiffer design. In that case the trusses would be all the same length and can be easily added.  The picture below shows variations with and without trusswork. My apologies if the design looks a bit half-baked… It is a work in progress. 

The idea of standardized, modular lengths brings up a question.  How long should the sections be and why? At the moment I am leaning toward shorter lengths for curves than I had originally thought, principally because I worry that longer lengths might not easily fit together in the field. (It looks like the roller coaster designer concurs.)  Also shorter lengths would seem to be more versatile, enabling a number of transition options. For example, a higher speed turn might incorporate several radii so as to not be too abrupt. Straight sections, I suppose, could be designed around what would fit on an 18 wheeler.  A pair of trailer length segments, bolted together, would easily span a four lane road with a turning and bike lanes.   

The problem reminds me of the slot car set I had when I was a kid.  I had several types of curved and straight track, all in short lengths, and these could be assembled into any number of layouts.

Finally, one advantage to dividing the track into “bite-size” pieces is that it would be easier to put a price tag on this whole thing. There is very little guidance on how much PRT hardware will cost, especially broken down in terms of stations, track, and vehicles. At least this would be starting point for the infrastructure part of it.

127> Really, Really Fast

As anybody does much design work knows, you can always do better. Second guessing one’s own designs is something that is best not rushed, however. So here I am starting from scratch once again, with fresh eyes and a few different conclusions.

There are several considerations that motivated me to rework the bogie design. First, I think I put too much emphasis on a system that could use off-the-shelf tires, even at high speeds. This led me to motorcycle tires. Actually, though, what is the function of a tire? It is for vibration dampening, shock absorption, and traction. Since we are talking about running on smooth (finger-jointed?) steel, it is mostly just traction that we’re worried about. The problem here is that to achieve it, tires create a flat spot where the tire meets the road. Taking the wheel “out of round” in this way increases rolling resistance. In other words, it wastes energy. Any emergency stopping should undoubtedly be done by clamping the track, and no standard tread design is going to climb very steep slopes anyway.  Finally, I suspect that it would be easy and cheap to outsource, even in small quantities, a solid rubber tire designed specifically for PRT. 

Secondly, there is the matter of flanged wheels. I don’t like flanges for hard and fast use because I if they are of a hard material, they will make noise and vibration. If they are of a soft material, the area making angular contact will wear quickly. This is because a flange is in effect, a wheel with more than one diameter. Since any given diameter will make a wheel travel just so far per revolution, if wheel portions with more than one diameter make contact at the same time, one or the other must skid to compensate. Thus you have designed-in a wearing surface. Position-locking angular contact can be made with equal diameters however. Consider the example of a rounded pulley wheel on a square bar. There, two point contact can be made and, if the materials are hard, there is little frictional tradeoff. Anyway, I have softened my position to consider using flanges because they so simplify the mechanics involved. There are better plastics these days, (such as Dupont’s Hylene) and with large diameters and geometries that minimize load, it’s worth a look, even for continuous high speed applications.  

  

Another matter that I have been recently considering more is the matter of aerodynamics of the bogie itself. If the bogie takes up all of the room inside of a box beam track, then it must push all of that captive air in front of it. Any bogie design must take this into account, and obviously smaller is better.

The design shown fits into a track with and internal height of about 20” (500mm) high. This is where I may have gone a bit overboard. You see, I wanted to fit the wheels with a commercially available hub motors and although I have seen many Chinese offerings from companies I have never heard of, these don’t even come with technical data sheets and are hard to design around. Unfortunately, western motor manufacturers seem to only want to design for a very large customer base, and really haven’t tried to get into the direct-drive vehicle business, so I was left with a somewhat oversized British offering. 

Protean motors are very powerful wheel motors which are designed to fit on ordinary cars with minimal modification or loss of power. Since I don’t want to design track that is too small to transport people at speeds they have already become accustomed to, and I don’t want to design a system that will constantly require wheel changing, these 16” offerings seem like a reasonable top end, as far as rim diameter goes. This does, however, make it into one heck of a hotrod. 

The Protean wheel motors, you see, produce (together) up to 320 HP continuously. (240 KW) These motors ARE the wheels, of course, so there is zero drive-train loss. So the thing can pretty much go as fast as we want. (For comparison a Tesla Roadster goes 125 mph (0-60 mph in 3.9 seconds) pulling  a roadworthy steering and suspension system, a transmission, and a 450kg battery pack at “only” 288 HP. (185 KW) So we are talking fast. Very fast.  Note that a motor’s power draw is proportional to the work it does, not its potential, so you still use very little power while cruising if the vehicle and bogie are well designed aerodynamically. In the pictures these motors are seen in green. 

The geometry that I am exploring in this design centers around eliminating upper guide wheels by having the vehicle press against a “ceiling” within the track to eliminate tipping or derailing when turning off of the main track onto a fork. The steering guide wheels are angled and flanged to fit more compactly. These guide wheels could also be external to the track, something that I have avoided for noise reasons, but my fears may well be overblown on that issue. Anyway, I have shaved a few inches from the track girth and, well, made a rocket.

126> A Few Good Destinations

In the early days of PRT, back when governments and multinational companies were first eyeing the idea, the whole concept was so futuristic that it was plenty enough to envision a standard vehicle, track and station and multiply them around into a grid, and call it a system. Back then it was a question of whether those new computers were capable of reliably and safely managing traffic flows.  As I was introduced to the concept, there would be a station every block or so, so that it would not be too long of a walk to get to one. The track would be one-way and you could get anywhere by circling around. Thinking back, maybe this just wasn’t good enough, and nobody realized it.  

Personally, I have had a very hard time trying to shoehorn the cities I know into such a scheme. It would be great if the funds were there to actually make such a comprehensive grid, but since they are not, it becomes a question of giving the most bang for the buck. But the systems that were designed for the grid model may not exactly fit the new roles. Moving away from a grid model has implications for the track, the vehicles, and the stations.  

Here are some typical situations that may exist outside of any downtown grid; The freeway commute - this calls for a relatively fast vehicle and outlying stations with lots of parking. The “strip”-  This is where eateries and retailers have reached a critical mass so that the  whole stretch of road has become like one long mall. It probably would call for two-way track that does not interfere with signs and driveways. Stations should be minimal footprint, perhaps designed specifically for private property, such as in the parking lot of a major retailer. Major destinations – Areas such as a museum district, a major hospital complex, or stadium need access to the system, although there may not be enough in the budget to put stations every half mile between them and other destinations. These call for large stations and a system with distributed automobile parking, since it is unknown where a visitor’s origin is, but it is likely that the first leg of the journey was from outside the system.

I think that each of these scenarios is extremely typical and each plays to the strengths or weaknesses of a given system design. True, these introduce design complexities that are much greater than what a PRT company would ideally want to tackle. But what is the choice? Try to interest cities in a “one-size-fits-all” system? 

In the end it is each city’s specific layout that must be addressed. Perhaps rather than a grid mentality, what is called for is a destination mentality. How can the most important destinations be served with the least amount of track and stations? That, after all, would seem be the best value proposition from the city’s standpoint. Yeah, I know... None of this really plays to PRT’s strengths. But PRT track is also cheaper and less disruptive to install, and being raised so as not to block crossing traffic is a huge bonus. So perhaps PRT can prove itself with less track and stations than the network we would like to see. 

A couple of points: First, parking. It seems pretty obvious that most people will have to park their cars to use the system. Maybe there are a few older cities out there that are teaming with pedestrians who live very close in. But for most of us, the construction of arterial highways has created a suburban landscape of car dependent homeowners and apartment dwellers. This calls for assessing each of the out-lying station’s potential to be a gateway to the system, and therefore a place to store the car in the meantime. Will merchants be willing to share parking in exchange for being convenient to the riders? Probably not in areas where people would want to park for the whole workday. Bottom line – Any system will need sufficient parking to support enough passengers to make the system viable. That potentially means thousands of parking spaces. It is likely that some stations will essentially be parking lots. Land costs are not inconsequential, so parking ends up becoming a factor in routing.

Another point is that in a landscape of very limited funding, shuttles (GRT) must be reconsidered. If the system is centered around serving the most important destinations, then it stands to reason that more people will be sharing a common itinerary. This has implications for track size, although we must avoid anything too big to be visually acceptable. The track I have shown in previous posts is about as big as I would want to risk. I think it is noteworthy, though, that technologically it is a simple matter to keep heavier vehicles spaced further apart than lighter ones to minimize weight concentrations on the track. I would keep it under six passengers anyway.  Such vehicles would simply share track with the PRT vehicles and move between high capacity stations. These would be “express” shuttles, so if your destination isn’t a main terminal, you would use PRT, which could service all destinations.

A last point about stations. I have opted for a suspended design mostly because such a system can drop to ground level and ascend with a minimum of station related hardware and track. Neither long ramps nor elevators are required, which is of paramount importance in a stripped down, budget starter system. A suspended system would also seem ideal for parking lots since PRT vehicles could go directly to your car yet there would be no track to cross.  

In a “destination oriented” design, the point would be to enable the rider to eliminate the lion’s share of driving from his/her day-to-day routine. The idea is to make all of one’s normal destinations available and convenient to the rider – shopping, dining, entertainment, etc. A well thought-out system could provide traffic relief that would ripple throughout the city’s side streets, not just the roads that parallel the track. This is because it would cut out what would otherwise be individual outings in the car. A few choice stations, (and some very lucky merchants!) would make most driving unneccessary.  Also, I cannot help but consider such a proposition from a tourism point of view. To some cities this is a very big deal. And, being elevated, it’s naturally scenic! 

So how stripped down could a system be? I guess I can imagine a single convoluted loop as a starter, but every city is different. Finally, I would add that there MUST be a way to branch track without a long shutdown. Any prospect of skipping over areas can only be temporary. Success will mean a demand for stations all along the track, so adding stations must be easy to do.  I posted a design for a branchable box-beam track in post 71.

125> What's in a Name?

 

I know, acronyms are often useless, contrived and perhaps a bit tacky.  And I suppose I could, in the past, be accused of trying to shoe-horn meaning into the word “SMART” or “SMARTS”, as seen in (posts 53 & 54 … Small-scale Modularized Automated Rail Transport System)  Now, of course, there is even the “Smart Car” to get confused with.  Well, here I am again, same word, new meaning.  I guess it’s a character flaw.  Anyway, here is one that embodies a point worth considering.

Standardized Multi-axis Automated Rail Transport.  There.  I said it. 

“Standardized” because it involves permanent (or at least semi-permanent) infrastructure.   Let’s face it.  Some VERY big companies have filed for bankruptcy in recent years and no city wants to be left holding the bag if their PRT company goes under.  If an untried infrastructure is contemplated, then “open-source” style standardization gives at least a bit of assurance that the track will be useful even if a given PRT provider goes belly-up.  Standards are everywhere in modern life and essential in almost every field of endeavor.  At the very least a system’s viability should not be dependent on a lot of proprietary technology.  Who would buy into that?  Standardization serves to extend the usefulness of any system by promoting development of parts or accessories by third parties, and gives them continuing incentive to innovate.  Standardized track would enable all vehicle manufacturers to compete and exercise their know-how, so it is a natural division between what is standardized and what is proprietary. 

“Multi-Axis” because the main obstacle to speedy ground mobility is the need for long ramps to switch from one level to another.  As I have pointed out in previous posts, objects moving around on a (2D) plane must either wait for each other to pass or leave that plane to go over or under each other. The larger the objects and the greater the velocity, the larger the ramp structures needed to accommodate this action.  Since the vast majority of traffic is in the movement of puny humans, building giant structures that rival the pyramids of Egypt all over the place is not a very rational way forward, especially in these days of fiscal austerity.  Although some PRT designs are essentially two dimensional, being raised to an essentially fixed elevation, I personally feel that this approach is shortsighted.  I fear that once PRT is found valuable and useful, a new generation of more versatile multi-axis designs will appear overnight that will leave these systems seeming quaint and old-fashioned and their track obsolete.  Of course that is just this author’s opinion. There are many reasons to “design in” the ability to ascend and descend within a small footprint. Some neighborhoods might wish to raise the track quite high to minimize the system visually.  In such cases the vehicles would descend to the stations, even if those stations were elevated.  There are cases where elevated stations are impractical or too costly.  Having sufficient stations is paramount, so being able, for example, to descend to ground- level bus stops or parking lots would be very useful.  Such situations would be impractical with long ramps, since they would tend to block private driveways and be visually intrusive.  If industrial or warehousing applications are considered, true 3D travel would be extremely useful. 

 Rail – Because it is smaller, lighter, easier to produce, transport and recycle, and can be designed to lock a vehicle on track in all situations, such as bad weather.  It is the best solution (short of flying) for true 3D mobility.  I know that rail is a contentious issue, and that many would say that a system like ULTra, whose vehicles could be easily be modified to freely roam any pavement is better.  Whereas I can understand this logic, I feel that the long ramps and the canopy effect inherent with such systems trump this argument.  Remember, even though the guideways may be only a bit wider than the vehicles, every time there is a fork for a station this dimension is doubled.  If there ever needs to be a two-way application, this implies up to four overhead “lanes.”   

Transport – not transit, because we are potentially talking about light freight as well as people, particularly at night.  In fact I see a lot of potential use in industry, such as automated warehousing and shipping.  I would point out that the whole way warehousing is currently done is to aggregate goods together to minimize many separate deliveries.  The ability to pick up and move small loads without a driver could change that,  allowing goods to be staged much closer to their destinations.  Taking some trucks as well as cars off of the existing road system can only be a good thing. 

This is a fundamental shift from simply calling for PRT.  Back “in the day,” PRT was revolutionary because it was automated and electric, but those features seem increasingly minor in today’s world.  Is the full automation of PRT really the point?  I could imagine a PRT vehicle that would be capable of processing passenger input on the fly… for instance a last minute decision to go around the block because you had mistakenly passed your destination.  Or perhaps a scenic tour… (“Take the next right.”)

So if it is not really about centralized automation, nor strictly about transit (for humans) what exactly is it about PRT that is so important?  Is it about “Personal?”  That is a bit troubling if by “personal” you mean transporting one person from a unique point of origin to a unique destination, at least in the short-term.  No early network will be that extensive, and skeptics need to see a shorter term payoff.  Is it the small payload we are after?  Partially; I would say that we are after payload-appropriate scaling, both in the vehicles and the infrastructure they run on.  This, of course, encourages the more extensive routing that meaningful networks require, thus leading to that promise of non-stop, point-to-point travel.  Naturally a smaller scale system can be much more economically raised so as to avoid traffic on the ground. These aspects, I think, should be the emphasis, more than “PRT” per se. 

When I try to explain PRT to people, their eyes glaze over.  PRT is the solution to a whole set of problems that must be considered in unison for it to fully make sense.  PRT is a “hard sell” for precisely that reason.  How can you get someone to sit down and try to imagine the limitations of all various future combinations of robocars, smart lanes, and electric cars if they are not so inclined?  Yet that is what they must do if they are to realize that these technologies aren’t the full answer.  If we want to sell PRT, we first need to be able to reduce it to its essence – to start with the aspects that no other system can match. 

Breathe deep and say it with me now… “We need a supplemental transportation infrastructure.”

There.  Feels good to put it into black and white, doesn’t it?  You’ve just cut through all of the explanation of PRT, Dual mode, etc. and put one of the world’s next great challenges into a simple phrase that most people can wrap their heads around.  We need a transportation infrastructure that is designed to do more for less.  One that can relieve us of the huge costs of continually building and maintaining more and more gigantic highway projects.  Stoplights are a ridiculous waste of time and cloverleaf interchanges are a ridiculous waste of real estate.  We desperately need a third option for economically crossing paths without waiting or colliding. 

We need a supplemental transportation infrastructure that is scaled to be appropriate for the task.  We have many, many small objects, (including humans) that are coming from many points of origin and need to be moved to many separate destinations.  These days it is no longer necessary to aggregate cargo and people into great groups and move them in mass.  (At least for land travel)  Modern manufacturing techniques can spit out hundreds of small vehicles with the same ease as a couple of big ones.  Electric vehicles don’t need to be big to achieve mechanical efficiency.  The land is already cleared and ready and we have plenty of infrastructure in place for heavy cargo in the form of existing roads.  There is no reason to build more enormous concrete interchanges when the traffic is coming primarily in the form of small payloads that could very easily slip by each other in a more appropriately sized system. 

I said it in my very first post.  We have to make people aware that the current roadway paradigm is insanely wasteful.  The future will be bleak indeed unless we make the kind of efficiency leaps in ground transportation that have been made in other fields.  It is totally crazy for 160 lb. person to need a 4000 lb. vehicle and eleven million pounds of roadway to get to a grocery store a mile away!  And yet not even be able to travel non-stop! 

  

Oh yeah, about that picture… If everyone in every vehicle just pulled over and lined up on an overpass (and they were all wearing white) this is what it would look like.  (What looks like a white stripe is actually about 120 little marks sized to represent people.)   Clearly this maze of concrete is insanely huge for the function of allowing those tiny white marks to move past each other unimpeded.  Since it must be designed to accommodate bumper-to-bumper fully-loaded eighteen-wheelers, form does not match function when it comes to moving these commuters.  Only one in ten vehicles in this picture is a truck, and it is questionable how many are traveling with heavy loads that could not be broken up. By the way, did you know that, in terms of smokestack-style industrial processes, cement production is second only to power plants in the emissions of CO2 produced? 

 

Let’s hone the message… We need a supplemental transportation infrastructure that is designed to inexpensively and efficiently provide fast, non-stop travel without blocking any other traffic. That can only be done with a system specifically designed for economical multilevel routing. Here, economical multilevel routing means small, and that is just as well, because it coincides with the idea of individualized point-to-point travel.   

A multi-axis rail system for transporting people-sized loads without getting in the way… Call it PRT or something else. Either way, it’s a “SMART” idea!  OK, that WAS a tacky ending…

124> While We're Still on the Subject...

Since we were discussing switching in the last post, and I have had a few ideas percolating about the subject for quite some time, I thought I might flesh them out in a drawing. The bogie shown above is nowhere near complete, but shows, at least conceptually, the hardware for aligning with the track and switching. The motors are direct drive, hub type. (in the wheels)

What I have attempted to do here is to illustrate a couple of possible solutions to what might be called the “too many guide wheels” problem. (Note: As I am getting this ready for posting, a review of past posts reveals that I have written MUCH more about this subject than I had remembered, with a great many similar designs as well. So to see some variations from the past, I would refer there reader to posts 67, 69, 79, 83, and 90.) OK: First let me remark about the problem itself. 

In the illustration from the last post, I show how a single pulley shaped wheel can be replaced by 3 wheels, a trade that seems of dubious value on its face. (Last frame, click to enlarge) Given the durability of some of the new plastics, in many cases it might not be worth it. I have been, however, primarily designing systems to more fully explore the requirements of the track. There is desperate need for standardization in PRT, and all designs have limitations. If a certain aspect of a track/bogie design inherently creates a speed or weight limit, this should be defined, quantified, and, if possible, overcome. I have therefore endeavored to design for very fast and heavy loads, with the thought that the track can always have lighter iterations if it is known that this will forever be sufficient. Designing for propelling such loads fast, silently, smoothly and safely no matter what (epic weather comes to mind) is a whole different sport than for more stripped-down systems, but it seems foolish to build the latter if the former can be built for nearly the same cost. Unlikely as that may be, only an exploration of the issues can reveal the truth. A good design must assume that the highly stacked luggage will fall, just as the passenger lunges to stop it, just as an extreme gust of wind happens, while the vehicle is just curving into an intersection. My efforts are not unlike the logic that brings car makers to the race track, where lessons are learned from pushing designs far beyond what will ever be expected in the field.

One point about flanged wheels; any material hard enough to roll on reduced points of contact will tend to transmit vibration, if not simply generate noise. Rubber wheels, on the other hand, wear faster but absorb vibration and noise. One possible compromise is to mount harder plastic running or guide surfaces on a intermediary rubber part, such as a large diameter ring or bushing.

While the pulley shape holds the wheel securely on the track, it does so by either allowing the friction of angular contact or by concentrating those points of contact onto a minuscule footprint. This is why roller coasters don’t use them. Yet the flanged wheel concept, or some version of it, is in wide and successful use in lots of applications and is often the best choice. Ordinary railroad track, for instance, is a variation that recognizes that the double flanges of the pulley design are redundant and that opposed singly flanged (steel) wheels will do. So what is really the minimum of flanges or wheels that is necessary for PRT? Surely the 24 opposing wheels suggested by my last post are not all needed. For one thing, it seems unlikely that 4 wheels should be needed to hold PRT down; Gravity should do that perfectly well. And we have seen with the railroad example that the wheel flanges themselves may not all be needed. A few down. What else can be done?

 

Note that track has spread for switching, although it is mostly cut away.

Also note that the widened "ceiling" is missing the guide. 

These illustrations explore a couple of options worth considering. First of all, the disadvantages of flanged wheels come from the effects of continuous hard use. In PRT, many of the flanges (or,alternatively, the corresponding opposing wheels) are only used in switching. Why then, would they wear excessively? The fact is they wouldn’t. Plastic flanges or wheels should work just fine for switching, even in high speed systems.    

Another situation is that guide wheels for switching must either turn continuously or engage and disengage. If they are to remain engaged, good practice would have them be large enough to not rotate at hyper speeds. At 100 mph, for example, a four inch wheel must turn over 5000 rpm, yet four inches is still way too big to start instantly rotating upon engagement. I have posted about this problem previously. By the way, one idea is not to motorize them but rather to use wind forces to keep them turning. Such wheels could be configured with turbine-like blades and since there is substantial captive air in the track that must be channeled around the bogie, keeping them turning should be easy. In this example, however, the main strategy is to minimize use of the steering guide wheels and to keep the centering guide wheels (the purple ones) spinning continuously.

Here I have brought back a very old idea… magnetic switching. In these illustrations, the eight steering guide wheels are small and intended as backup only. The main steering is from the electromagnets (red) attracted to the steel switching strip. (blue) In these illustrations it can be seen that when there is no switching, neither the drive wheel flanges nor the steering guide wheels need get any wear since lateral control is maintained by guide wheels (purple) which are always engaged, save for the moment where one side or the other ceases contact for a few seconds due to the track widening as it branches into two directions. I have included a fifth “hold-down” drive wheel, which provides the geometry to inhibit forces that would otherwise twist the bogie inside the track. (extreme sideways wind gusts for example) It has a plastic groove down its center to receive a rounded, bogie-centering guide, which, like the drive wheel flanges, will get minimal use.  Because I contemplate the potential for very steep or vertical  (elevator-like) travel capabilities, this “hold-down” wheel could help facilitate that purpose as well, were such a scheme ever considered worthwhile. (There would be an addition traction means for this beyond those five wheels, however, such as ordinary "cog railroad" methods) Note that that upper rounded track guide (that fits into the hold-down wheel recess) is missing from the last picture, where the track has been widened as it would for an "off-ramp". That piece would resume further down the track for the each divergent branch. 

I am becoming more and more inclined to give up the idea of pneumatic tires in favor of semi-solid rubber. I really don’t think the bumps created by well-engineered expansion joints warrant that kind of cushioning, and I don't believe custom rubber castings are all that expensive. The flanges would be of a long wearing plastic, such as is used for casters and roller coasters. They can be replaced separately from the rubber. One of the keys to this system is the recognition that the flanges and the rest of the wheel need not be a unified piece or of the same material.

Finally, this track gives a nod to the typical roller coaster track architecture in that the design, as shown, involves bending round pipe only, so there is no compound bending, as would be the case with angle steel or square tubing that must curve sideways and up or down at once while keeping its profile plumb and level. The various steel profiles are shown as unwelded, separate pieces. This arrangement makes banking the track so easy that it begs the question whether it is worthwhile having the self-banking characteristics exhibited by my (and some other) suspended vehicle designs. That, to me, is more about budget,business plan, timing and politics etc. A general purpose bank would do no harm unless it was at the wrong angle for what ended up being the running speed at a future date, if the vehicles could not self-bank. But that is a debate for some other time. Also there is no trussing or triangulation shown as would generally be the case for any larger spans. Nor is there covering over the track in these examples. I kept it minimal for clarity.

In summary, this general design provides full, secure containment of the bogie on either side of a track that is widening to form a "Y" even without bottom support from both sides. (It is fully “half-track” capable) It has no more than seven wheels in active contact at any one time, and those seven are optimized for constant duty. All flanges and steering guide wheels are for (more or less) extraordinary events. Switching guidance, centering within the track, and securing the bogie during extreme events are different issues and the wheel style, profile and materials can reflect this. My general recommendation is use detachable flanges to ensure safety from extraordinary twisting or inertial forces, but to minimize their use by making them redundant in general use. This is done with the centering guide wheels shown in purple in the illustrations. In switching, temporarily engageable, self-turning wheels are used but may only be a secondary safety system if magnetic means are used as the primary way to get the bogie to hug one side-wall or the other. Discontinuous top guides can also be employed.

123> Thoughts on Track Size and Switching

Well, I’m up in New England again, away from the modern world, and probably posting this from the town library.  I have gotten to see both the Atlantic and Pacific oceans in this past month, and had a fair amount of time to think along the way.  And there is something bugging me.  It’s the track.  It’s too big.  I mean, take a look at this.

This is a now defunct “Santa’s Village” out in California.  True, it is supported every 20 ft. or so, and true, it went VERY slow…  But still, does PRT track need to be THAT much beefier? 

The answer is no, if you ask Asko Kauppi. (known to many of you as the frequent contributor to this site “akauppi”.)  His vision of PRT, shown below, runs on nothing more than a pair of pipes.

 True, it may not go very fast, handle steep slopes in ice storms, or draw power from the track.  But still, it can be argued, it would provide very decent mobility in most situations – and at a fraction of the track cost.  Could such a minimal track ever work in America?  Certainly, in certain circumstances.  But we Americans like to get places fast, and there’s a lot of ground to cover in our sprawling cities.  So my designs speak more to the needs of the longer distance commuter market.  Yet I think there are several important lessons to be learned from the design. 

First, it runs on a “half-track”.  That eliminates half of the cost right there.  What is a “half-track” you ask?  Funny that it should come up now, because I recently was mentioned in a “Transport Innovators” posting regarding switching for suspended PRT.  The fact that the viability of switching suspended vehicles was not all-together settled, in the minds of some, led me to re-examine the issue, if for no other reason, than just to explain the concepts in a more understandable way for my readers.  I decided to use primarily illustrations rather than words, and opted to put it all into a single picture.  (Suitable for framing! lol)  Be sure to click on it to enlarge.

 I would emphasize that the last picture is probably the most important, because it holds the key to understanding most of the mechanical drawings on the subject.  (found through patent searches, etc)  I would also point out that most systems do not anticipate the inertial forces that would require so many wheels as the last picture would imply.  I know from experience that some end up being included solely for the possibility of a freak, powerful blast of wind just as the vehicle is switching tracks.  Steep slopes also contribute to the need for the wheels to completely capture the track at all times.  So when I refer to a “half-track” I am speaking about an arrangement such as in the first illustration. 

Asko’s design is not the only one that runs on a “half-track.”  Ollie Mikosza’s “MISTER” system is a suspended system that pioneered the concept for PRT.  There are some new visualizations  for his system, and it appears that he has abandoned the structurally superior but complex triangular truss design in favor of the sleeker, much easier to build three-tube design that is universally favored by rollercoaster makers. 

 

So why not just go with the MISTER/rollercoaster style track?  I have several concerns.  First is the fact that it is open to the weather.  Ollie seems sure that snow and ice are not a problem but I’m a natural skeptic. There is also the matter of limited surface area for traction and braking, and the matter of noise.  I will say right now that these are largely higher speed or higher load issues, and not necessarily a problem with the MISTER system as it is designed.  I am curious, though, about how to safely carry the electricity to run the vehicles in an open track system.  In the case of Asko’s BM One design, the vehicles are battery powered. This obviously cuts track costs and there is no shock hazard.

Anyway, I have, so far, opted for a covered design.  I am not sure, though, that it ALL must be covered. For example, the track as I have specified it seems over-designed for many “last mile” applications.  Consider, for example, a large residential subdivision where there would be little or no through- traffic and speeds would be very low.  Perhaps a central loop would put all within walking distance.  It occurs to me that perhaps a vehicle could get around such an area on battery power alone, and that a cheaper, lighter, open “half-track design might be appropriate.  So far I have designed to include highway speeds and even faster.  Could such a vehicle also operate on a stripped-down, ultra-cheap half-track?  I will be devoting considerable time to this question…from my Yucatan hammock.

 Oh! And speaking of hanging around in the woods… Take a look at what was hanging over that little structure I am building when I arrived! One tiny little oak tree saved the project. It took a lot of cable to lay that sucker down in the driveway. And yes, that’s me, in all of my country scruffiness.

122> Still Toying with Trikes

Well folks, they say a picture is worth a thousand words, so here are a couple thousand worth. Shown above is how a three-wheeled PRT vehicle could be tipped forward to create a ramp, and how the swing-arm can be detached to allow the vehicle to travel away from the track.  The second picture illustrates how the swing-arm can be used to tilt the vehicle back to give it a more even aerodynamic profile.  In this embodiment I assume that the vehicle will not be roadworthy, and that it would have very limited range and speed on battery power.  The steering would be accomplished by having a pivoting back wheel and independently controlled front wheels. The rear wheel would extend downward for boarding, and retract for high-speed use, as shown. 

In this design windows were minimized to avoid the high air conditioning requirements of a vehicle with lots of glass.  Anything short of completely automated driving, however, requires high visibility for the driver, even if the vehicle only goes 10 mph and is controlled by a joystick, so some configurations might need more glass than what I have shown.  I envision the ground-driving capability to be primarily for parking lot use, for either ferrying people to their cars or from the PRT station to the front door of a store or other destination. In this capacity it would go one way empty, on autopilot.  Allowing passenger control risks taking a vehicle to where it could get stuck or get into traffic, so perhaps the manual-drive option should be limited to privately owned vehicles. Such personal vehicles, in addition to the extra glass and AC requirements, could also have extended range, greater speed, more ground clearance and better suspension.  The bogie would only accept a limited amount of weight, however, so such modifications would be at the expense of payload capacity. After all, if we want to have cheap, extendable track we need to draw the line on weight somewhere. In the example above the extra hardware (two motorized drive wheels with rudimentary suspension, rear pivoting wheel with a screwjack for tilting the vehicle forward and a small battery pack) adds an estimated max weight of (perhaps) 100 lbs.

121> Solving Traffic with 3D PRT

The other day I read a paper promoting “robocars” and related technologies and I ran into the following quote:

“There are two weaknesses in the PRT idea.

1.       1. The need to construct new infrastructure. PRT proponents argue that the guideways would be light, requiring little space.

2.      2. There is no good reason why the vehicles must be held captive to the guideway.  Vehicles captive to the guideway are called Single Mode (SM) and those capable of operating off the guideway are called Dual Mode. (DM)  There has been considerable discussion of the merits of each approach.”

Let me quickly address the author’s second assertion.  I would point out that the obvious reason for holding a vehicle captive on a guideway is speed, which clearly relates to issues like safety and weather.  The author indicates, through this assertion, that he envisions improvements that are, at best, incremental.  OK; on to the main topic.

The article got me thinking about something that many PRT advocates seem to get, but many otherwise rational and educated people completely miss.  I will state it as bluntly as possible, because it occurs to me that only very distilled concepts seem to get traction (and funding) in our society.  You know, “war on terror,” “no child left behind,” etc.  Effective leaders understand the power of a sound bite.  I know that I am “singing to the choir,” and I know my readers are much more astute than most, but I have heard too many discussions  where even the most well-read PRT people stumbled around on this issue.  So here it is, boiled down to two pithy sentences, ready to pull out at the next opportunity.

Efficient urban transportation at ground level is a physical impossibility.  Therefore the best transit solution will necessarily require a whole new infrastructure.       Period.   End of story.  

It is simple physics.  Objects moving in different directions on a single plane will either bump into each other or have to wait for each other.  This is the universal truth behind traffic.  By moving in groups this effect can be minimized somewhat but never eliminated.  The best solution to urban congestion, by far, is to move in three-dimensions.  This, and only this, gives many-fold, rather than fractional improvement. 

Consider that once-modern, transformative invention, the superhighway.  Can you imagine eliminating all of the overpasses and putting stop lights in their place?  Each and every overpass can, in a sense, be thought of as a wormhole, a portal, that effectively eliminates a standstill condition in two directions.  A highway can even be thought of as a string of traffic solving overpasses, with the higher speeds just being a byproduct of this linear arrangement.  

It is the ability to leave ground level – to go from 2D to 3D - that makes efficient high-speed urban transportation possible.  You can have a 200 mph bullet train, but without getting off of the ground, there will be people waiting for it to pass all along the way.  And all of that wasted time adds up, even if it is distributed.  By the way, this example illustrates two important points, which I will call “Herd behavior” and “Saturation”. 

In herd behavior, which is the 2D version of flocking or schooling, many move as one.  This is the animal kingdom’s mimicry of fluid dynamics.  In the case of the bullet train many passengers are moving as one, like a herd, and very fast.  This is a great dynamic but it becomes decreasingly effective as cross traffic becomes denser.  At a certain point the traffic slowdown created by cars that must wait for the train to arrive and then pass creates compounding gridlock that would otherwise not exist.  A related problem, found along freeways, is the fact that underpasses are often few and far between.  There is just no free lunch with fast ground-level travel in the city. The slowdown is just distributed in a way that obscures the cause and effect.

   

Or take the example of a four-way crossing.  If there are only a few cars in town, obviously there is little chance of delay.  An intersection might only need a yield sign.  With moderate traffic, timed lights and other means can help greatly by moving groups in unison. (Like a herd).  To illustrate, consider how fowled-up things get when a traffic light is broken, so it is treated as a four-way stop.  Yes, moving groups in unison really works, and all kinds of clever routing and timing schemes are in common use.   With high-density traffic, however, a point is reached, which I will call saturation, when nobody, in either direction, “makes” the light.  In this case each stoplight necessarily cuts traffic flow by over 50%.  The avoidance of this degree of saturation should be the first object of any remedy.  Indeed, all of the potential benefits of robocars, intelligent lights, contraflow lanes, etc. fall into this category.  They don’t even attempt bidirectional non-stop movement.   

It is the difficulty and cost of building a 3D road infrastructure that is responsible for our traffic.  Roads and the vehicles that travel on them can only go up and down gradually, high-speed or sharp turns lead to skidding, and roads must carry extremely high weight loads.  It is impossible to use overpasses and cloverleaf interchanges on every block.  So nothing that runs on roads, as we know them, will ever be more than a “Band-Aid” solution...  The cost and space constraints of roadwork will keep cars largely earthbound and in each other’s way, and this will limit speed and efficiency.   

So the logic is very simple.  We need to move under and over each other to get around a city efficiently.  It may be cost prohibitive to do this with cars and trucks, but people are light and easy to lift, and account for almost all traffic.  Therefore it stands to reason that a very good solution to our problem is to start with the creation a 3D infrastructure for moving people. (and not, say, cement trucks)  If that is the starting point, logic ends up dictating the rest of PRT design.  I would even go so far as to say that a measure of the effectiveness of an urban transit infrastructure is the ease with which it can utilize multi-level routing. 

The PRT message has become muddled.  Now, when people think of PRT, they increasingly envision publicly rentable robocars.  Having a designated guideway that is really a roadway in disguise misses the point.  Any efficiency gains that such a system produces will almost certainly be at the expense of other forms of transportation.  I do not believe a network of golf cart lanes is the answer for in most cities, and having the self-driving vehicles for them doesn’t change that.  In any case, if it is non-stop, it is either elevated or it makes someone wait.  PRT, in my opinion, should no longer be all about automation or being electric.  The real key is that PRT is the only model which can cost-effectively initiate the transition toward a fully 3D urban transportation network.  Personally, I think the question of private vs. public vehicles, PRT vs. dual mode, is secondary as well. 

No, constructing a new infrastructure is not a liability.  It is an opportunity to take a quantum leap in efficiency by specifically designing for 3D space.  And making the vehicle captive would mean much higher speeds in any weather, and allow electricity to be fed to vehicles directly, eliminating the efficiency losses associated with batteries.  This infrastructure would, at last, be appropriately sized for the job, and so would move many more people per dollar spent, and do so with almost no physical  footprint.  It would be blazing fast to construct and could also provide invisible housing for unsightly and weather-vulnerable utility wires, as well as house next generation street lighting.  It could be engineered to allow silent vehicle movement, even with highly efficient hard wheels.

But this new infrastructure, unlike improvements such as fiber optics or gas pipelines, will not be decided in boardrooms, and so requires a degree of generalized public understanding to get traction.  We need sound-bites so simple even that the “experts” will get it.  We need to win the war of the pundits.  It is they who echo ideas until they become commonly accepted by the masses.   

A NON-STOP URBAN TRANSPORTATION NETWORK… Not a too bad a phrase.  If only we could get industry and academia busily pursuing this as a goal, they would return again and again to what we already know to be the answer.  Then maybe some of the funding that is going to improving legacy technologies worldwide could be shifted to where it would do more good.  We already can’t afford to maintain the pavement we have. How long are we going to continue to throw good money after bad?