Friday, August 7, 2009

45> A Critique of PRT International’s Design Approach

In my last post I ended by wondering out loud about whether anyone significant was actually endorsing the vehicle-mounted linear motors. After I thought about it, I remembered a slide in the PRT International streaming lecture, and so I have just listened again to Ed Anderson’s explanation of the various design trade-offs from his perspective.

Let me be clear, first of all, about one thing. I would love to see any PRT, including the design embraced by PRT international, implemented by some city, somewhere. There’s a lot to skepticism to disprove and much to learn. I also have great respect for Dr. Anderson and his work, and sympathize with the position he is presumably in, having investors to answer to. He has to, for their benefit, defend the exact design choices that moved forward, even as technologies change over time. Some “sound-byte” logic and “glossing-over” is to be expected anytime the politics of business is in play. That being said, it drives me nuts, and so here I am again. The last time I went off on this poor guy was only a few months ago. Of course, with 30% new readers each week, and an average viewing of only about two minutes, most readers won’t know the difference, and so, if you are new to the site, you’ll find some pretty smart people have weighed in on this general topic in the past, if you are interested…

First though, I think it is worth noting that there is a fundamental difference in vision that leads to the design differences. There is no need for PRT International, or any other PRT vendor, to have a product that will work in every city. Indeed there is strong incentive to create the simplest design that will work for the most profitable situations. Even if the design is useless for 95% of a city’s transit needs, it is only the lucrative 5% that is of interest to the PRT vendor anyway. If that seems cynical, I would point out that I think those numbers are very high compared to light rail. My environmentalist friends, however, should brace themselves for disappointment at the limited scope of change that PRT will bring, at least short term.

I, on the other hand, believe in the network effect, and see any limitations, especially budgetary, as potentially lethal. The spread of the railroad, for example, was transformational in a way that is similar to the internet. Both would have been economically viable on some scale, even if the build-out costs were, say, ten times as much. But both designs proved versatile and cheap enough for a massive, world-changing implementation, wherein the existence of the network itself created whole new businesses. That’s what I like to think about. PRT 2. All that having been said, here’s what I don’t like about the PRT International approach.
1. First there is inability to go up and down steeply or sharply. This has spin-off disadvantages galore. It’s not just the cost of raising the stations, but the political cost of lowering the track so the stations don’t have to be so high. Ed Anderson points out that, for a given track height, a hanging system is more visually intrusive. When track has to be kept low to keep station costs down, that is a concern indeed. He can never really contemplate raising the track way up, which is probably the best way to address local opposition to a proposed track segment. Also, although it is never ruled out, it is pretty obvious that bringing one of his pods to ground level is not very likely to happen. In other words, access to the system from a bus stop or private parking lot is pretty well abandoned. Again these limitations are not particularly important in the urban configurations he is designing for.
2. Second is the linear motor. I just believe “wheel” or “hub” motors are better, and that if they had it to do over, they would use them instead. The Linear Induction Motors (LIMs) have major efficiency drops with anything but very close “near contact” with the track, which must be outfitted, for it’s entire length, with a “reactor” plate. How much does that drive up the cost of the track? Also keeping the LIM close creates limitations on track design, specifically on sharp turns up or down. (As in, say, dropping down to a station from a higher track level) This is, again, is not much of a limitation if you are only talking about getting around downtown, and your cost basis is already less than the competition.
3. Then there is the issue of needing to bank turns. This includes the track on either side of the turn itself. In a truss system this has got to be expensive, especially on tight turns constricted by landowners not willing to cede right-of-way. Again, in an urban environment, competing with massively expensive systems like light rail, this is not such a big issue. If it can’t go fast or make sharp turns, so what? Neither can the competition. It’s an issue if you want the fixed part of the system “dirt cheap” so it can be massively expanded, however. Or if you see your ultimate competition as the automobile, not light rail, or if your ultimate objective is green prosperity through mechanical efficiency rather than moving on to the next big contract.
4. Finally there is the issue of stuff getting into the track. If on the ground there are serious potential problems ranging from flooding to peoples feet getting stuck. Even raised there is the potential for freezing rain being blown in and accumulating, or the more exotic sandstorm. In the PRT International presentation, the position of the LIM facing downward indicates that the reactor plate sits directly under the track’s slot, where debris would enter. I will be the first to say, I am certain that this is not news to them, and that a remedy has been engineered. But it is one other advantage to a hanging system, with the slot on the bottom.

In conclusion, I believe that the PRT International/Taxi 2000 type design has limitations that would need to be overcome before it would find wide acceptance in anything other than inner city use. This is largely because what seems to be the simplest, most straightforward design has the unintended consequence of simplifying the cars at the expense of the track and stations. Therefore the design has less chance of achieving the “network-effect,” one of PRT’s primary advantages over other forms of mass transit. The design has very little utility for the delivery of freight, so this is one potential loss of revenue, especially at night, when the track would be largely empty anyway. (limited routing precludes freight anyway) The use of LIMs doesn’t seem to solve anything worthy of modifying the whole track for, because there is no reduction in moving parts. I believe wheel motors to be more efficient both as propulsion and brakes, and, unlike the LIMs, they are sealed.

However, as anyone who has studied my designs well knows, a truly flexible, very inexpensive system involves many other tradeoffs as well. In particular, the tradeoffs for cheap track and stations involve some pretty sophisticated engineering on the vehicle side. In practice the daunting challenge of any PRT vendor will be to become a bridge builder, vehicle manufacturer, and public works contractor, all at once. Starting with a very simple design is, in practice, essential.

In the US at least, transportation projects involving road “improvements” follow a totally different path than mass transit, being drawn up years in advance and being triggered by road usage reports. There is currently no business model for entering that market with PRT. Mass transit involves a more holistic approach, cracking the door for more “out-of-the-box” thinking, giving the opportunity to PRT vendors to air proposals. I do not want any of my criticisms of current designs to give pause to any transit authority official or city planner anywhere. Period. I believe they will work, as promised and engineered, and probably well beyond expectations, for the stated purpose. I just hope companies like PRT International, if they start making money, put some of it into developing a product for commuters.


Ollie Mikosza said...

I am Ollie MIkosza, designer of MISTER system, which you mentioned kindly in your blog earlier.

I sent you an email yeterday, mentioning few of the same problems you talk about in this blog entry.

I agree with many of your statement and arguments. E.g, that first PRT vendors will have to be "do it all" businesses. And MISTER, for that matter is. We even have several cities, which have given us Right of Way and permission to build, but no money. It is ironic situation, isn't it. Wile our design will guarantee a high profit marging and capacity transit, with 30% higher capacity than a 200 person LRT line going every 3 minutes - yet we cannot find investors. We cannot even convince any city yet, to sign with us, say, a 20 year CONDITIONAL CONTRACT for services, whereby we only get paid if we meet contract terms. And one of those conditions would be that we must payback to the city same amount as they have contracted - i.e. it would be ZERO cost to the city. But having such contract would enable us to get money from banks. While cities are happily paying to bus and LRT operators on long term basis, without any guarantees of zero cost - yet we cannot break thru this barrier of brainless bureacrats. Perhaps this is the problem, as important as the PRT design, which you can address in your blog?

A kid should understand, that if someone offers you something on a condition that it works and brings money, otherwise you don't pay - than you are not risking anything, are you?!

We have calculated that with our 7 mile (10 km km) PILOT system we can move 15 million passengers per year (some 50,000 x 3 mile trips per day with average of 1,5 person in a vehicle, using only 27% of system capacity), charge $1,00 per such trip and make 30% profit, while net cost to the city would be ZERO. This offer was sent to several Polishm US, UK and Middle East cities. Guess what? NO REPLY!
Of course, with the growth of the system, profitability grows, so we even offered to share it with cities. Still - NO REPLY.

Regarding the technical issues, I agree entirely with your perspective, while disagreeing with Ed Anderson and alikes. He might be the "father" of PRT World, which does not mean that he is God or that his dogmas are unshakeable.

Suspended systems, no matter how the vehicles powered, are clearly better than supported. From climb angle to passaenger comfort and safety, which is critical factors. In addition, in suspended systems track can always be "flat", i.e. without superelevation on turns, while in supported it must be angled, which substantially increases costs. In addition, cost of stations is much lower for suspended systems, as you do not have to "dig" so much, if at all.

Visual effect of suspended system being supposedly more ugly is a pure nonsense. I bet anything, that truss or beam guideway, but positioned 10-15 me above the ground will be less intrusive than Ed's, never mind ULTra, Vectus or 2getthere going 5 m above the ground.

Debrie, snow, sand, ice will always be a problem for supported systems, while it is not for MISTER or your design.

Thanks for your efforts to help PRT cause in the interest of all people. Because we will all benefit, as well as the ecology of the planet. In 20 years people will forget that it took so long to get it going.

Ollie Mikosza

Anonymous said...

I read, in one of Dr Anderson's papers, that they chose supported over suspended because it made riders feel more secure - not because it was technically superior

Ollie Mikosza said...

Dan mentioned in his blog entry that it was about "aesthetics" but both arguments are pure nonsense, witout any foundation.

If it was a feeling of insecurity, then how come that lifts these days are both closeted and on the outside of amny buildings? It somehow does not reduce their patronage, although being suspended in a glass cage 100 m above the ground should frighten people much more than 5-10 m. And people riding in cable gondolas or chairlifts, also "survive" quite well, not to mention all those who use aircrafts.

Even if a small proportion of people would not chose to use PRT for fear reasons, it would be less than 1%, hence negligable and without any econonic effect on the service.

Anonymous said...

Nice to see Ollie here!


I agree with your points, but how about just plain IGNORING the Taxi 2000 project. Like Apple has been ignoring Linux for all the years (and still is). Not that that comparison is fare, but anyone seeing your design and theirs should be able to tell one can work, the other one... not.

Maybe there is a reason why they have never become a big business, yet. Maybe its not the government, or not the (whatever). Maybe their design is fundamentally flawed, as you carefully point out. I agree. But I don't care to mention them - it's a waste of time.

Also, I find their current name a joke. What does the International mean there, really. Why not say "PRT Local" and start with something local. Or - why not say "PRT Galactic" while we're at it? International is tasteless and vague. imho.

I hope I won't regret these words. Sorry if I hurt anyone (but Dan started it...) :P

Dan said...

Dan the Blogger Responds-
Hi, Folks, I've got to break this comment into two, since I used too many characters.
Ollie, it is indeed nice to hear from you. Your designs have been very influential to my thinking. You are right about the need to address the obstacles PRT developers face in a post or two. (or three) I hesitate to get into the subject here in too much detail, or I'll be out of new ideas when I write that post. I will say that it’s hard to say much about it without referring to the insights offered in an essay by Nathan Koren, which Akauppi introduced me to last spring. ( ) I also feel that there is a problem with confidence. I spent many years in the contracting business, and I know the time and difficulty in assembling a motivated team with the right attitudes and skill sets. Personally I think it would be extraordinarily hard to assemble a team capable of building a PRT system from anything less than an ongoing company already engaged in similar activities. There are also issues of depth of top management. Did you see what happened to Apple stock when it looked like Steve Jobs would be leaving? For that matter do you remember what happened to the company when he left the first time? The replacement CEO was stellar as president of Pepsi, but ran Apple into the ground in no time. The smartest of people can run into problems. Then there is the matter of depth of resources. Got a few million to handle the unexpected? Addressing confidence issues is a very big deal, even for huge, established companies. Here in the US we generally expect everything to go wrong, and everybody to be a crook, and require all kinds of hedges and insurance policies before anything gets done. Sad but true. Anyway, it is a huge hurdle, and I hope to write some posts on the subject soon. As for your second comment, I agree completely. I do, however, include a particularly beefy looking support beam on my designs which is just a cover, meant to look like it is strong enough to lift a small building ;) PS. got your email, will respond soon.

Anonymous, glad to have you back…or maybe it’s not you! Hmm… I read the same thing, and thought it was pretty weak. The Cabintaxi design he referred to was like a moving box for fairly large groups, if I remember right, and could ride above the track or below it. It looked odd and dangerous when hanging. Kind of like a levitating Winnebago. (A boxy American travel-trailer) From the pictures it is no wonder passengers preferred the top. I really think he was justifying his own design more than being objective.

Dan said...

Dan the Blogger Responds, Part 2
Akauppi, Welcome. Be careful about mixing up the Taxi 2000 and PRT International systems. There was a messy divorce, and I have been reprimanded by readers for not knowing about it. Actually, the more I study PRT International’s design, the more I like it, except for the points I mention in my post. As Ollie has pointed out, getting a first contract is a very, very hard thing to do. We Americans are into cars, and having lost market share for years, are keenly aware of how hard it is to produce one that really lasts. I will say this for PRT International’s design. It is very minimal, Very simple. When someone asks Ed Anderson why he thinks he can become an overnight producer of vehicles that won’t break down, he can point to the fact that his design has, maybe, 15 moving parts. (I cannot say the same) If he hires a respected, local contractor to do the work street work, and the same for the stations, he has gone a long way towards addressing the natural fears of potential customers. I do not think there is anything stupid about designing for the realities of the times, even though it may be disappointingly tiny niche market. He also has shared a lot of details that others have not, something that is, in my opinion, a great service to PRT in general. I, personally, have learned a great deal from his many writings, and am grateful that they are out there as a resource. I critique his work out of respect, not distain. Once upon a time, he made a business/design decision toward simplicity over versatility, toward shuttling people in the inner city over the commuter market. He has since made a life’s work based around that decision. I cannot blame him for sticking with it now. Only time will tell. There is certainly nothing to be gained ignoring him or throwing sticks at him. He may be the only realist among us.

Bengt Gustafsson said...

I just wanted to mention that the Taxi2000 system does have a slot in the bottom of the guideway which is about twice as wide as the top slot, which makes most of snow, sand or whatever fall out immediately.

Similarly, the Vectus track is very simple to bank in curves as it has these saddle-like parts between the main structural tube (which is about 600 mm diameter) and the rails. Just by sliding the saddle towards the inside of curves the banking is accomplished during installation of the track.

Conclusion: Don't think that people are fools just because you don't grasp their ideas immediately.

This said, I still think that a suspended system is superior. On the other hand one of the major drawbacks is the higher position of the track as it requires more sturdy foundations to keep up with moments from wind load. So the higher levels of 10-12 meters is not for free, mind me.

Also, at least for Uppsala, the officials I work with there are very worried about height, indicating that the 11 m overall height required with two level crossings is *much* worse than the 8 meters required with one level crossings. I don't really see how they could be so sure about this view at this stage, but the voices were very load and clear around the table.

Bengt Gustafsson said...

What I have heard about the Cabinentaxi user preference study there was a slight overweight for prefering a supported configuration. And while the cabintaxi cars do lock very boxy the technology is very well worth looking into, for instance by going to their patents. After all, this is the only time in history of mankind that a suspended PTR system has ever acquired a permit for running with passengers (and at a headway of < 2 s, unheard of since). It is also the larges test track with the highest mileage of vehicle testing...

I don't know why they ran 12 passenger vehicles, but most would at least be PRT. Maybe lack of confidence in the capacity. IT must have made the guideway substantially larger...

cmfseattle said...

"I really think he was justifying his own design more than being objective."

Let's see some numbers.

Dan said...

Dan the Blogger Responds-
Thanks Bengt. Your insights, as usual, are worthy of consideration. The "saddle" design for track banking did not go unnoticed here. It is shared with the Raytheon design, which had an even bigger central "tube" that the "saddle" part could be mounted on. I don't know about you, but I can't help but notice that that saddle, made smaller and turned upside-down, might not be a bad option for a non-free-swinging hanging system..;o)

cmseattle; I can't give you numbers, I am just referring to Ed Anderson's own words,"somewhat more people preferred riding above the guideway than below." For the complete text, refer to my May 10th post and click on the link, "point-by-point." However the reason I said that was because, as Bengt also alluded to, the Cabin Taxi system in question had huge boxy 12 passenger compartments hanging by invisible means, like a travel trailer glued to the underside of a raised highway. I just don't think that one can objectively draw concusions about the much smaller, obviously well-attached "pods" I endorse from the Cabin Taxi example, and the fact that the reference was made at all, in my opinion, makes Dr. Anderson's objectivity suspect. I stand by the statement.

Anonymous said...

I think the box-beam design you are criticizing is quite sensible. Yes, it does have some limitations, but I don't think it's anywhere near as bad as you portray it. Indeed, I think it is more than good enough. ULTra has been successful in getting business, even though it is much more limited, by comparison.

I think the reason for this is that PRT suffers from a most unusual problem: it is simply too good to be true. Authorities are so used to subsidizing inefficient, loss-making transport systems, that when a PRT vendor comes along saying "I can move thousands of people per hour, cheaper than a bus, and still make a profit if you let me build my system here", their immediate reaction is, "This person must be lying; there has to be a catch... we just haven't spotted it yet."

As for the Cabintaxi design being boxy, I think that's mainly because boxy was cool back in the 1970s when Cabintaxi was designed. If Cabintaxi were implemented today, they might give the vehicles a more streamlined or rounded shape.

cmfseattle said...

Dr. Anderson is probably aware of wheel/hub motors. microrail is working on a vehicle that uses wheel motors. I don't think he'd choose them, even if headways were kept to 3 seconds, because of the need for accuracy when calculating emergency stops. On page 6 of Safe Design: "LIMs used for
braking satisfy these requirements since they provide reliable braking independent of friction, whereas
braking through wheels does not."

I also recommend reading his Supported vs Hanging PDF. As for passenger opinion polls, if you asked whether passengers preferred to travel at ground level or on an elevated rail, which do you think would win? The point is that unless you run the numbers, you don't really know.

Also: in a turn on a hanging PRT system, wouldn't the support posts need to be on the inside of the curve? If the posts were on the outside, how big would the "question marks" have to be in order to prevent vehicles from hitting them? You should run the numbers for a cost comparison of a 75 foot-radius turn (Taxi2000 minimum) using 60-foot spans (especially if you have investors to answer to).

cmfseattle said...

I forgot to ask: where did you see the PRT Int. design with LIM reaction plates next to the upper guideway slot? I guess he was working on a new design for PRTI, but I haven't watched the entire stream, yet.

The Taxi2000 design has the reaction plates/running surfaces next to the lower guideway slot. They even tested their plow design

And another thing: Anderson wrote a truss vs. pipe guideway comparison.

Dan said...

Dan the Blogger Responds-
Hi, Anonymous… I don’t exactly understand your comment, as far as the “box-beam” term is concerned. Imitation is the sincerest form of flattery, and my design IS a box beam. I even came up with the same dimensions, within a couple of inches. Mine is just turned upside down to allow docking anywhere, even an open-air bus stop. I do not dispute that the PRT International or Taxi 2000 designs can beat the pants off of the non-PRT alternatives in the markets for which they are intended. I do think, however, that a path forward toward less automobile dependence is a worthy goal, and that means addressing the commuting portion of transit, not just downtown. As I tried to explain in my post, the commuting PRT is a different animal from the downtown one. The track must be cheaper, the cars faster, the stations more minimal. There will always be a PRT traffic density below which any segment of track cannot be justified, cost-wise. This is, of course, related to fares charged, etc. I am simply pointing out that at the suburban ends of a system, there will only be significant traffic during rush hour, and traffic revenues will only be fraction of what current companies, including ULTra, are designing for. This does not mean they aren’t good, viable systems for their targeted ridership.

Hi, cmfseattle,…Thanks for the many links. I either never heard of, or at least not kept up with, that Microrail site. I am looking forward to exploring it, and I always like the spread of ideas, so post links freely!

As far as your first observation is concerned: I agree, kind of… It is absolutely true that the LIM based braking (and all motion control, for that matter) is independent of traction of the wheels, and that is great. Heck, it’s fabulous. It’s like a tractor beam. But it is also true that there are inherent inefficiencies and costs, which I have previously mentioned. I do not pretend to know the extent of these with Anderson’s design, or Skyweb, since they do not specify the exact distance between the LIM and the reactor plate, or the nature and cost of that plate. A great deal of my problem with LIMs may, indeed, be solvable or already solved. (almost no flux leakage, highly efficient induced magnetism in a reactor plate that doesn’t increase track cost significantly) I just, personally, doubt it can be done. Therefore I have endeavored to look at alternatives that do not increase track costs. I would point out two things. Wheel motors brake magnetically, like LIMs, (not by friction) except they can possibly skid within the track. This should never happen, however, or something went very, very wrong. A couple of posts ago I discussed some strategies for emergency stops several of which would work with “track on bottom” designs, most notably clamping the track itself if all else fails. It’s not elegant, but it should never be used anyway, and it doesn’t increase track costs.

Dan said...

Dan the Blogger continues his long winded response-
About the turns. Yes, the posts should go on the inside. Investors? This is just a hobby I try not to put too much time into. I want to point out, again, that I am not designing a downtown system, or attaching any kind of business model to this thing, or I would make design choices that are very much more like the systems I critique. I am musing about possible ways to someday build a commuter system that can go into down town. Everything is different, including suppositions of constant speed, set radii, etc. The radii you site are designed to be banked and taken at a fixed velocity by a constant stream of vehicles, like a freeway. Freeways have high throughput but are expensive to build, especially considering the cost of right-of-way. There is also another model that can get you where you’re going, and that’s the dirt-cheap network of back streets. If the track and stations are cheap enough, and the network is extensive enough, then the whole model changes. I do not believe that the eventual optimal system is one that requires 3-second headways to turn a profit. That precludes the suburbs and therefore the commuting market. The system I envision can turn radii so small, if necessary, that only one car can be on it at a time at whatever speed the passenger prefers, up to the speed limit for that turn. Like I say, it’s a whole different animal. As far as the supports, go, whether is a question mark, a “T” “C”or “7” or a duel footing A or upside down “U” design- I have to say, I’ve worked with a lot of steel is and it is very stiff stuff. Cantilevering is not a big expense structurally. Also once you are digging a footing anyway and have the equipment and crew on site, anchoring for a non-balanced load is, in my opinion, no big deal either. I think Anderson overstates the issue, as I’m sure I said in my “I Just Can’t Let This Go Unanswered!” post.

Re: Your second comment- I think I got the mental picture from his PRT International stream. It was very quick but I believe the LIM was facing down and the reactor plate was where Skyweb’s slot is. It is not by the top slot but directly under it. My concern was ice buildup on the plate. As for Skyweb’s LIM, I cannot tell much from these pics. Are they using the guideway itself for a reactor plate? Is it vertical or horizontal?

I just want to reiterate: I am just trying to envision a system that is cheap enough and versatile enough to go way out into the suburbs. Therefore I have to investigate any design barriers to this end that are inherent in the systems designed so far. I am not advocating abandoning these designs, and I have repeatedly stated that I have no business model for adoption of my ideas. That is for other people, probably far down the road. (BTW I probably should change the flash animation, since it is more contentious than my present attitude, and actually was a reaction to the Raytheon model, as was my entire blog originally.)

Ollie Mikosza said...


I agree with you that any version of LIM motors is an expensive option, which can be equaled by simple means. Breaking by clamping is also our (MISTER) option. We also have "cog wheels" in all inclines and other areas, which require high momentum and slow speed (e.g. 45 deg climbing).

Anderson's arguments for benefits of supported systems based on the twist momentum on curves and natural frequency problems are overstated in importance, hence a nonissue for suspemded systems.

I also want to mention that MISTER design solves commute and last mile problems in suburbs. We designed it for speeds of 90 km/h (55 mph) for suburbian haul, 30 mph for CBD and 75 mph for intercity (up to 200 miles). And the last mile will be solved when the automated city travel is perfected (see Mojave Desert Challange). Then our pods will be Dual Mode vehicles, transfered automatically onto the self driving palets, which will deliver you to the door, pick up somone else in the vicinity, then go back and reconvert to PRT at the transfer stations. Street driving will be done at the 20 mph, as you are only going 1 mile from the neares station. In this way you will have all of the functions required without the need to build overextensive guideway network or too complicated vehicle fleet.

And the cost of 2-way guideway with average of 150 vehicles and 10 stops per mile being a total of $10 mil/mile, seems more than reasonable, doesn't it?

I read somewhere that Toronto will spend US$40 bln for refurbishment of their road and tansit systems over next 20 years. I bet it will solve nothing in that time.

And for this money MISTER could build 4000 miles of its guideways network, 40,000 stops, 600,000 vehicles capable of moving some 1 million people at any one time (average of 1,5 person per vehicle) and with throughput of 30 mil passenger-miles per hour. Now, these are realistic figures with 50% of theoretical vehicle capacity and more than Toronto needs even at peaktime. It shows what the PRT can do.

Yet, all those ignorant and self serving bureaucrats and politicians etc., will rather spend this money on creating more headaches and problems. But the time will come, when this will become reality and we are working hard on making it happen in our, including my, lifetime.


Marsden Burger said...

Just to set the record straight; from the, 5,000 plus, rides given to the public on the Cabintaxi development facility, 49% preferred the upper level and 51% preferred the lower level. While these were the final numbers reported to our marketing staff by our site operations people, no one can say for sure what the margin of error was in these percentages, but I am more than willing to admit that it probably was more than 1%. :) To draw any conclusions about preferences of people for supported or suspended systems within any future population and relating to any future PRT system, using this interesting data, is obviously meaningless.

That said, with no inherent biases for one system over the other,(and recognizing that the over and under approach allows for the best urban area integration)I prefer the ride of the suspended vehicle. My reason is the ride feels more solid on the lower system. The lower vehicle has a given natural sway to it that intrinsically leans with you into the curves. The supported vehicle has to be manipulated in some fashion to overcome the natural feeling to “tip over” as it starts into a curve. This is not a flaw of Cabintaxi any more than it is a flaw of an automobile on a curve or a rail vehicle on a curve – if you ride the Wuppertal Monorail, you get the same solid feeling as compared to the Chicago El.

Still, it is not a big deal either way – 49% 51%

Dan said...

Dan The Blogger lost track of this thread but is back...
Hi Ollie, Marsden.
Ollie, as you know I like your design work. I am particularly impressed with the ability of your track to branch without requiring deconstruction of the original line. Very nice. I do wonder though, don't your wheels have to go over 3000 rpm to get to 55 mph? Aren't you worried about your bearings and the wheels themselves overheating and/or wearing out? PS. Try to love your bureaucrats! They're just afraid they'll make a mistake! ;o)
Marsden, Thanks for setting the record straight. I have long suspected that hanging would feel better. I wonder what you think of the whole motion sickness debate. I would think hanging would be better in that regard especially.
Your comment here prompted me to revisit the Cabintaxi archives. I hadn't seen the better YouTube footage. Actually I was pretty ignorant about the whole project. There's a lot to learn from that endeavor. I wish you'd turn over some specs! LIMs aren't really my favorite way to go but with all that has been done,.. well, Someone should really get that project polished up for the big dance. Lemme at it!