Sunday, June 27, 2010

92> Crack in the Track, Jack...

In my quest for the optimal hanging style PRT track I have found yet two more factors that could influence overall profiles and dimensions. But first, let me offer something to new readers who may not be convinced that PRT is a good idea in the first place.

I recently read a critic of PRT espousing the argument that automated cars would bury PRT because they would not require “new” infrastructure. I’m pretty sure the author hasn’t had his large front yard turned into 2 extra lanes and a median like I have, or he would realize that we are putting in thousands of miles of “new” infrastructure every day. Road construction is so “baked in” to the society that we no longer question or even notice it. I would wager that there isn’t a person in a thousand who has any idea of how much of their own personal money goes into road construction annually. When you find out you just might want to join the Tea Party movement.

More automation is coming to personal transportation. That is for sure. But with the current infrastructure that means trying to automate vehicles on icy roads, amongst texting teenagers and lost, darting pets. What will be the automated vehicle’s response to a downed power line? When it wants to go back to manual mode will the driver be available in time? Or caught looking something up?

Honest acknowledgement of the need for infrastructure that is safer for self-driving cars leads to a healthy debate about what it should be. Do we need it all to be big enough for trucks? Do we want to have to salt and plow it in winter? Do we even want it on the ground? Do we want it to enable fast vehicles or should we just slow down and save fuel? Do we want freeway-like non-stop service? If so, how is this best accomplished? Can we leverage what is already out there, in terms of existing roads and bridges? Should we limit the vehicle size since we know that people, given the chance, will choose obscenely oversized ones? What about the larger debate over urban planning and development?

Yes, we need new infrastructure, and yes, some of it will need to be ordinary roads and bridges. But roads are mostly used for single individuals going to particular destinations, and are, frankly, way overbuilt for this purpose. Even without PRT, it is time to re-examine our infrastructure requirements and consider putting down something that is less wasteful of taxpayer’s money. If we want a cheaper, minimum-footprint, longer lasting transportation infrastructure that is designed for fast, appropriately sized, automated vehicles, then we are basically talking about PRT. PRT is a logical outcome of a very logical debate.

Now on to the picture.  Back in Post 83 I showed a track profile with the actual running surface areas in red. This, as you can see, is that track but in the form of a crossing. Clearly there would be some loss of guidance as a bogey passes through, but not enough to be critical in any way. Also note that the wheels must span a two-inch crack in the track. This weighs into the wheel size debate because a smaller, harder wheel, without a special preventive design, would hit the gap hard, whereas a larger inflated rubber tire would glide right over it.

Such a crossing also raises old debates about “brick-wall” stops and the spacing between vehicles, and reminds me to consider the possibility of a failsafe track-based braking system.

It is reasonable to at least consider such a scheme for PRT because it could make merge and crossing collisions impossible by physically keeping two vehicles from entering the same space. So far I have not even considered how such a system would be designed, but something like a tail-hook comes to mind, which should not influence track profile all that much.

Here’s the second factor that could influence track dimensions. When I was first considering these matters, I recalled the ill-fated involvement of Raytheon in the PRT designs pioneered by Dr. J.E. Anderson. Upon their breakup, Dr. Anderson did extensive public polling and redesigned his track accordingly. I had always thought that Raytheon’s track was ugly and my initial reaction was to simply applaud this new, thinner rail.

I have, however, subsequently come to question some of his conclusions. Specifically, he was designing for the very narrow range of applications that were viewed as most advantageous commercially. In these dense urban environments, there are many factors that make setting supports very costly. Hence he opted to go for long spans, even though it meant relatively costly trusses. Contrast this to the approach taken by Higherway Transport Research. 

This illustration shows a how a track profile very similar to mine can be made by roll-forming a few lengths of steel. This can be done on relatively thick stock, by the way. My books have cold-rolled square tubing with up to half-inch wall thickness. Without critiquing this design specifically, I would just say that it illustrates how more frequent supports can greatly simplify the structural requirements of the track. For long runs, along freeways, for instance, there are no buried utilities, no streets to block during construction, no driveways in the way. A higher amount of track noise is acceptable, and there is less worry about the visual impact. I suspect that cheaper alternatives exist to the long spanning truss designs I have shown. 

All of this opens a larger debate about a factor in support spacing and design that I am not well versed in. That is the matter if regional soil types and the best way to anchor to that ground. In some areas, bedrock is very close to the surface; while in others there is sand or clay many meters down. Would Dr. Anderson have gone for the long spanning trusses if setting supports only involved simple drilling, as would be the case following freeways in most gulf coast cities? If miles of track were required in such a situation, what would the optimal span between supports be? Would many lighter supports be, in the end, more practical? After all, this would limit the weight any single support would have to bear. I still believe the truss design to be very important, in any case, since spanning intersections with multiple lanes requires such a design anyway. Still, I really haven’t considered the ideal freeway following configuration, which would be very important in young Sun-Belt cities like Houston, which have urbanized along the freeways, more than from the city center. 

By the way, Speaking of Higherway… designer and founder Tad Winiecki has an interesting suggestion as to the type of tires to use. (Alert readers will remember my search for a small but heavy-duty, high-speed tire for the tilted wheel motor designs.) He suggested small aircraft tires… I’m looking into it.

Anyway, those are my musings for this week… And so, signing off from somewhere near Crack-in-the-Track, Texas… This is Dan the Blogger, wishing you all a good night!

Sunday, June 20, 2010

91> Dan the Blogger was Writing ...

“Dan The Blogger” was writing a comment (to alert reader Andrew F) and decided to just go ahead and make a post out of it. (I refer to myself in the third person as sort of a joke, as well as a way to be found slightly more easily on the Internet) The comment was about putting utilities in the track, and here are some observations:

Electric companies keep themselves pretty busy repairing electric lines that are damaged by ice, wind, auto accidents, etc. Recently, in Louisville KY, the tail end of a Gulf hurricane darkened much of the city for weeks, and then, a couple of months later, a severe ice storm did the same thing. There was a public outcry. The electric company reported that the only real solution would be to bury the wires, something that they estimated would cost about one million per mile. That was that. The poles remain.

Actually, in spite of the cost, buried lines carry a fairly large percentage of the electricity in the U.S. But the wire is not totally safe there either, and one city reported a digging accident, on average, every single day. There are also problems with water intrusion and corrosion. So what I take away from this is that even with the cost and problems of buried lines, it is still widely considered worth it. They have never dreamed of the kind of sheltered accessibility that the PRT track would provide.

Meanwhile, in San Francisco, a lawsuit was recently filed against the electric company for polluting the ground water. Wooden telephone poles have been treated to prevent rot with a host of nasty chemicals, mostly illegal these days, and are known to leach these poisons into the soil. Millions need replacing annually because of rot, which, if you think about it, is actually the process of the wood itself turning into soil, preservative and all. At some point this practice will stop. Any electric company that would proactively take out the poles and the dirt around them before they were forced to do the job under regulatory scrutiny would be doing their shareholders a big favor. And they would look good doing it.

I wonder then, about the prospect of offering to house a mile of those electric lines safely for a mere, say, $900,000? That’s about $170.00 per ft. enough to pay for all of the steel in the trusses I showed last post. Those poles need to come out eventually. It is just a matter of time, and the contaminated area is expanding as we speak.

Then there is the matter of street lighting. Most streetlights are outdated, by and large, both in electrical efficiency and design. As a person who flies a fair amount, I often stare down in wonderment at the sheer volume of energy used to light all of those city streets below. Although the typical sodium vapor is quite efficient in many respects, LED lighting has the potential to vastly reduce energy costs over all. Apparently, as sodium vapor lamps age, they require high and higher voltage to stay lit, eventually exceeding the capacity of the ballast, and the light will begin to flicker, then flash intermittently, then go out altogether. But another aspect is the whole notion of always flooding a large area with bright light even when it is not needed. You can’t put dimmers on sodium vapor streetlights.

Way back in post 14  I illustrated PRT track based street lighting. It uses many little directed spotlights to illuminate objects on the ground without blinding drivers. When drivers are not forced to stare into the light they need less of it to see, hence less wattage is required. Furthermore, much less light is needed at, say, 3:00 AM than at 10:00 PM, because there is almost no traffic. Having many smaller lights enables energy saving schemes where, for instance, half of the lights are turned off in those wee hours or are on motion detectors. More savings. And of course there is the matter of not needing a ladder truck to change the LEDs, which last longer in the first place.

The point is that the city, too, has a potential financial benefit from PRT track, aside from the transportation angle. By the way, this money is your tax dollars at work. In Los Angeles, for instance, each 50’ property is assessed $70.00 per year to keep those streetlights on. Not only will PRT make a street quieter, (over adding a traffic lane) it could directly save the effected property owners money.

Another aspect is the possibility of using solar cells on top of the track to eliminate the electrical costs altogether. Even amorphous (cheap) solar cells produce about 5 watts per square foot. This means the track could produce, say, 10 watts per linear foot. I would guess that this is pretty close to sufficient for the kind of system I have in mind.

I must say that, as an era, this is not one where the “winds of change” are blowing very hard. Perhaps people are a bit overwhelmed by the pace of advancement in communications and computer related fields. It’s certainly not like the sixties, when every car needed fins and taillights that looked like booster rockets to celebrate our entrĂ©e into the “Space Age”. At any rate, it seems people are in no mood for their government to try anything new with their tax money. Can you imagine mega-projects like the interstate highway system or rural electrification getting passed today? PRT is going to need to be seen as having multiple, tangible, short-term benefits as well as those harder-to-explain ones that most of us already understand. It will need to be structured in a way gauged to gain friends in high places and to have multiple levels of public appeal.

No black outs and tax savings – That’s a start.

Sunday, June 13, 2010

90> Let's Take It From the Top

I want to go back to the beginning in my discussion of PRT track, specifically track for hanging style PRT, for the benefit of the majority of readers who have not followed the ongoing development of the corresponding SMART (Standardized Modular Automatic Rail Transport) specification.

The most fundamental concept that needs to be understood is that of switchless steering. Unlike a railroad, which requires a track segment to be mechanically moved to provide switching, PRT designers have generally agreed that this can be more easily done by the cars themselves by means of engagable/disengagable guide wheels. These require a vertical surface to engage upon. Since the main wheels (or even a Maglev system) require a horizontal running surface, the two, in combination, look something like this.

 It should be noted that only one half of this book-matched arrangement is theoretically needed, except for places where tracks are merging and diverging, though leaving the redundant half in has advantages (load distribution, simplicity of symmetry) which I believe out-weigh the disadvantages. This picture,
from post 54, illustrates the concept.

The second concept is the combining the functions of multiple wheels into one. A look at a roller coaster wheel setup  shows how multiple wheels can hold a vehicle tightly to a track. A simpler approach, however, can be achieved by the use of flanges, as on a train wheel, or dished in or out wheel or track profiles. The angle of contact, though, in such systems, should be as close to a right angle as possible or the flange will tend to wear out, since it introduces a point of friction to the system. A quick look at my older posts will show various examples of radii on both wheels and track.

A third concept is that plate that keeps appearing in my track designs, pictured below.

Whenever a tube-like structure is bent, it tends to flatten out in the process. If a section of track is spanning a great distance and is bearing a great deal of weight, the downward forces will tend to want to flatten, then fold the track under that weight. Stopping this flattening arrests this tendency and strengthens the track. In the case of an encased track with a slot in the bottom, the initial flattening would cause the sides to fold inward or outward, thus narrowing or widening the slot. These plates, placed periodically, prevent this. In the second picture you can see how such bracing can be connected by long plate steel to make a complete box beam. Personally I find this design ugly and worry about single wall designs for PRT because of noise, condensation, and uneven expansion.

A fourth concept is modularity. Almost all discussions on PRT touch on the possibility of movement of goods as well as people, particularly at night. Additionally, many envision a variety of vehicles, and the current diversity of motor vehicles that populate our roadways would tend to bear out the desirability of this approach. Such ideas are not put forth by actual PRT vendors, however, since it currently would be counterproductive for them to develop and offer a confusing array of alternatives. Then there is the matter of routing. Long commuter type routes would call for faster vehicles or possibly vehicles for groups, if there were sufficient numbers of people with common origins/destinations to support this scenario. Therefore there would seem to be a very strong case for creating a track that is compatible for all or any of these vehicle types or speed ranges. This logic leads to a track profile where smaller vehicles are compatible with the track of the largest anticipated vehicle type. I submit that this “largest vehicle” would be GRT. (Group Rapid Transit) In the U.S. many cities have “Park and Ride” systems already in place, which aggregate passengers in outlying suburban locations. I would not want to rule out shuttling in these passengers in groups of, say, 10 or 12. Although GRT is a contentious issue in PRT circles, it should be noted that from a track design point of view, there is very little difference dimensionally between the two. Heavier gauge steel, more frequent supports, or simply spacing heavier vehicles more sparsely are ways to accommodate such a possibility. Whereas PRT track could be made smaller (in profile) than track for GRT, the size of the truss that is required to span reasonable distances can fit either. I would suggest that any such heavier track be used for arterial routes only, because cost is everything when it comes to expanding limited routes into meaningful networks, which, after all, is what PRT is all about. This modular approach recognizes that no one set of engineers is liable have all of the answers as to the very best vehicle design.(s) any time soon. Therefore I suggest removable running surfaces. This has the added advantage of reduced noise, a smoother ride, and essentially no chance of condensation. It also looks to a future with possibilities like Maglev. In order to accommodate the largest number of vehicle types I suggest something like this general shape.

The design allows for several centering means through the use of either convex or concave surfaces. My only concern is the fabrication of this profile, especially radiused sections for turns, because the required roll-forming equipment for that is not universally available on a local basis. Although I have tried to keep my designs easy to produce anywhere, this may be something that would need to be shipped in. I suspect, however, that many local job shops would be happy to fabricate the shape by splitting stock pipe and making curves by a tack-and-bend-as-you-go method.

Although I promised some further thoughts on use of tension cables to extend the span of track sections, I would like to put that off for the moment and return to standard truss design. As far as box trusses go, the round tubular type seems to be acknowledged as the strongest, and was the choice for the Skyweb Express demo track. I believe 90 ft. was the maximum span.

It has the disadvantage, however, of being relatively complicated to fabricate, because the pipe ends must be cut to match a curved surface. (I have seen the tube ends are flattened in some applications) I have wondered about this for some time, as it seems that square tubing would be so much easier, since it just needs to be mitered. Nonetheless, in most demanding situations, such as cranes, these complex joints are almost universally used. Here is a picture showing he complex cut. These have just been tack-welded.

In the illustration below I have taken a similar box truss but substituted those plates for the verticals. Because the plates are only rigid in one direction, I have stiffened them by joining the upper and lower gussets into a single piece. I have also used simple miter cuts on the diagonal pipes, again, using gussets to reinforce the joint. This is not exactly to scale and the diagonal and horizontal pipes don’t even touch in this picture, (much weaker) but this is just a conceptual drawing. The general design should, however, be very strong, cheap and easy to build anywhere where CNC flame-cut plate and pipe is available.

In the next picture the red surfaces indicate the running surfaces for a PRT bogey, taken from Post 83.

If it looks like I haven’t decided exactly what becomes part of the truss and what becomes removable, you’re right! I have not. There’s also a radius missing. It’s a work in progress. Also not shown is the skin, and provisions for electrification, communications, carrying utility wires. There’s plenty of work to do, and now you all know were I stand at the moment. For shorter spans or hanging sections, BTW, the design would be completely different, but, as they say, “One step at a time.”

Tuesday, June 8, 2010

89> On the Road Again...

I am in the civilized world once again. Well almost. The bus I took from Dartmouth to Boston had wi-fi – just no AC receptacles. My poor old laptop only holds a charge for about half an hour these days, so the planned two-hour bloggathon had to be cancelled. That made me wonder what will happen when those upcoming electric cars start stopping on the road for lack of juice. Yeah, I know, they will be have low battery alarms, quick swap battery packs, and there will be charging stations… But that won’t do it.

With gasoline, when your tank is almost empty, you have a certain amount of time to get to a gas station, and it is a fixed amount. A limited amount gasoline will always get you roughly the same distance, even if your car is old. Not so, batteries. When they get old their performance falls off of a cliff. That means that just because a 60% charge got you home with juice to spare 4 months ago, there is no guarantee that a 75% charge will get you home today. Couple this with the high costs of batteries, people struggling to make ends meet, and human nature, and it will be roulette by the masses, with many making shorter and shorter trips, until one day it happens to them, just like it happened to my laptop on the bus. I was almost finished with my research when BOOM! Windooze lived up to its name. Involuntary hibernation. I predict that the only meaningful way to solve this dilemma will be to automatically slow the car down to walking speed before the battery is finally exhausted. That will force people to deal with the problem or at least get them on to the shoulders. Someone should patent that. Oops.

Another thought occurred to me, sitting on that bus. I was considering the effort that was taken to blast away the granite hills to make way for the road. And such a wide swath of land.  I guess the wide median is to make oncoming traffic lights less blinding. And now it will need mowing forever more. It made me consider the hypocrisy of “saving the rainforest” without starting first a little closer to home. When my computer died I was trying to learn a little something about “carbon credits”. The whole concept of paying someone not to burn to offset the burning that you must do would seem to be a concept with some relevance to systems like PRT. I wonder, for instance, about the carbon emissions of a highway, about viewing a given stretch of highway as a CO2 producing system, including factoring in the loss of CO2 sequestering forest that such a system requires. (I wish they could also factor in habitat loss and fragmentation)  Isn’t a highway a bit like a coal burning power plant? What if highway land had to be offset with carbon credits? Thought of in that way, elevated PRT starts looking pretty good.   

As I approached Boston, computer tucked away, I couldn’t help but notice how expressive cars are. These days there doesn’t seem to be much taste for expensive, formal clothes, so that leaves the car as one of the few mobile ways to resister our social status to the world. That’s a very basic primate behavior and not easy to break. And it runs so much deeper than just status. Carmakers can make us feel masculine or feminine, outdoorsy, socially conscious, sophisticated, elegant, fun loving, daring, young, reasonable, powerful. Take your pick. You’ll feel that way and project that self-image to the world. That role is pretty hard to replace with a public transit system. Even one with wi-fi and AC.