Sunday, May 31, 2009

35> Troubled

I am a troubled by the business model that would-be PRT providers are taking, either by choice or necessity. The first thing that troubles me is the lack of emphasis on the transformative potential of the technology. I understand that they want to be professional, to focus on immediate doable objectives. But the immediate doable objectives are such that they really are not “the only game in town,” but rather an arguably risky way to achieve a limited set of goals which may not be that well suited to PRT in the first place. It is no wonder light rail is so vocal in its derision or PRT, since the PRT companies have chosen light rail as the sweet spot in the market. Somewhere in the mix, the whole promise of PRT goes missing.
I would like to see a long-term vision for PRT adoption added to the mix. Without that, the future of PRT could just be the sporadic limited construction of incompatible systems, assuming that they all work as advertised, are within budget, and don’t end up being a technology principally beneficial to the makers of the deal.
Is it not possible to go head-to-head with roads, instead? To be a commuter alternative instead of a downtown crowd shuffler? I’m afraid the limits of design and business imagination have led away from the true value proposition; a better alternative to the network of urban/suburban highways and roads. It is the power of that network that makes the automobile (and therefore eventually traffic) ubiquitous.
I will say it again. The true value of PRT is that of a substitute for cars and roads, not a substitute for light rail or trolleys. PRT companies need to figure out a way to leverage the full value of proposition of their product. I would submit that that would entail a fully articulated long term plan that reaches well outside the realm of what one company can do. It requires all PRT companies, environmental groups, standards organizations, as well as partners in government and education. Until they have a plan for a system that you don’t need to commute in your car to get to, I’ll keep reminding them.

Saturday, May 23, 2009

34> Access for the Disabled

Bengt Gustafsson ( ) in his comments on my most recent post reminded me of a subject that has been long troubling me; Access for the disabled. I think I read somewhere that in one of Ed Anderson’s many attempts to get a project going, he was rebuffed when he tried to offer a special vehicle for the disabled and had to do a complete redesign after his idea of requiring wheelchair bound travelers to sit sideways was ruled out. Apparently every serious design is now bigger, heavier and more expensive than would ordinarily be the case. The track must also be heavier, meaning more support posts, and heavier vehicles take longer to stop, as well as consuming more power to operate. In other words, ADA (Americans with Disabilities Act) compliancy for a uniform fleet will hugely and negatively affect the cost of the whole network. Getting appropriations for infrastructure is already a challenge that restricts the scope of such projects. ADA compliancy, if they are unwilling to budge on these issues, can only mean leaving more areas unserved. Don’t these people see what they’re doing? A fully implemented PRT network would open new worlds for anyone who cannot drive, especially the elderly and disabled. Waiting a minute longer for a special vehicle would be a very small price to pay.
Unfortunately the language of the ADA is in fundamental opposition to efficient PRT. PRT should take advantage of the fact that the average occupancy of a vehicle is only 1.2 persons, by optimizing for the common case and hence saving an enormous amount of energy and infrastructure costs. The ADA seeks to absolutely equalize the perceived experience for the disabled to the standard experience- but since the disabled require additional resources, this in turn forces us to expend additional, unnecessary resources on each and every rider. While an identical experience for the disabled is a nice ideal, the conservation of diminishing world resources and global warming are far more pressing.
So how about this; the vehicles come in two or more sizes. I know that seems like a lot of gratuitous headache and overhead, but I can think of no other option. Rather than have a special vehicle for the disabled (which has been deemed unacceptable) I would suggest segregating the fleet into two weight classes, with the lighter being only for a couple of passengers with luggage, for example, and passengers with any more than that would call for the heavier model. This would include anyone with need for such a vehicle, not just the disabled, such as families. The control software would dial the headway way up for the heavier vehicles to minimize the weight factor, which would not adversely affect system performance much because of the proportionally low ridership of the vehicles.
These heavier vehicles should naturally cost more, but the handicapped can always be given a discount, I bet that kind of discrimination gets little challenge.

Saturday, May 16, 2009

33> In Defense of the “Track-on-the-Bottom” Design

After my last post I received and email from an industry insider in defense of the track-on-the-bottom design who gave me some facts and figures to chew on. One of those, the proposed height for the stations gave me cause to pause. It was much lower than I had envisioned. This got me thinking. What is the lower limit on raised station height?

One of the problems I have pointed out about bottom track design is that track descending to ground level would block driveways and invite climbers and graffiti. But what if the track only descended to, say, 9 ft.? It would still block some driveways from tall trucks, but the impact would be much less than going to ground level. A “not so raised” station would presumably be much cheaper to build. It’s a thought worth considering.

I still believe in the hanging vehicle approach, personally, but I don’t pretend to have a business model for it at this time. Companies don’t need to solve the whole “transportation/traffic/climate change/wasted productivity/polluted world” thing to have a viable product. A PRT system for (fairly) flat, high volume urban areas is a viable and needed product. It’s not all things to all people, but it is a foot in the door. I think we could call that “PRT I,” and what I am thinking about “PRT II.” I will be glad to see any kind of PRT take root, but those companies should be preparing for PRT II, (not necessarily my design, but the expanded role and capabilities) even as they endeavor to sell PRT I. That is simply keeping ahead of the curve.

As for my design work, I am still hard at it, although I have little internet access and even limited electricity for the time being, as I am at my cabin. I have been designing the old fashion way, with pencil and paper. I will say, though, it looks very promising. Very tight turning radii both vertically and horizontally, very fast speeds, climbs of any angle, (right to vertical) great acceleration and braking. Beside the gondola design, one thing that sets my designs apart from the status quo is the articulated drive unit, which is for better traction and tighter turns. A two part unit will have twice the wheels. Add to that that my switching scheme requires redundant wheels and now you have a drive unit that is bristling with wheels, all needing sizing and placement. This could take a while. So, from the town library in beautiful Canaan, NH, this is Dan, signing out!

Sunday, May 10, 2009

32> I Just Can’t Let This Stand Unchallenged

I have just finally gotten a few days to devote to PRT and have spent some of it studying PRT International. I am glad to see that a lot has changed since the days of Taxi 2000. One of my major peeves, the huge track, has been replaced with a stronger slimmer skinned truss. The control system apparently will allow for more and variable speed. The one problem I have with it is the top riding design. In the site there is a point-by-point comparison by Ed Anderson. The arguments are pretty thin, I’d say. I would invite my inquisitive readers to open it up in a separate window so as to get both sides.

It starts with the fact that it is harder to do switch. I’ll certainly admit that. That’s point (1) Then in (2) it says that vehicles on top look better, and that they have so much experience we should believe them. The gondola design hangs 8 feet lower; the theory goes, so it is closer and more visually apparent. (Of course the part that is always there is 8 ft closer but anyway, to that I say, “OK, if it’s really a problem, let’s raise the rail 10 or twenty feet.” Oops! There’s a problem. If all your stations need elevators, I guess you don’t want to do that, do you? Especially if your system isn’t designed for slopes. The next point (3) deals with the costs and size of foundations and supports. Please. What about the costs and foundations for elevator-equipped stations? He says the weight is off balanced, doubling the stress at the ground. First that isn’t much of a problem, Second, it doesn’t take an aerospace engineer to see that you could make a “?” shaped top to the supports and balance the load if it was a big deal. As for (4) and (5) he makes some good points that took some pretty fancy math to figure out. I’ve studied the equations as best I could and will not quibble about the conclusion of the study which says that, in effect, if all else is equal, then hanging vehicles have essentially no structural advantage. Fine. But all else isn’t equal. I have seen studies where municipalities have voiced concern over corner “clipping,” (that being where right-of-way is needed over valuable corner property) to put in a proposed turn of PRT track. Now I don’t pretend to know exactly how sharp a turn his vehicles can make but I would bet they would lose a cornering speed contest.. In point (5) he talks about “natural frequency.” I really don’t think that will be a problem if the turn is essentially a right angle, because that will always involve two closely spaced supports anyway. It will also require slowing for the turn and quick acceleration out of it. By the way, about banking the track- What speed to you bank it for in his system? Gondolas self-bank to the proper amount for any speed, a fact left out in his comparison. Anyway, by his own figures hanging wins point 4 and I say nothing in point 5 really tilts that balance. As for (6) I really think he is just looking for another point to make. He implies that hanging vehicles need more beef. Note the qualifier, “all else being equal” and the actual wording “the sidewalls will be heavier.” I suppose that implies that if one looped a couple of steel bands around one of his vehicles and lifted it, the sidewalls would collapse. He should have claimed overall weight advantage, and I think there probably is one, because of the added functionality of the hanging design, so I’ll stop and just give him that one. I would maintain, however that it is a minor point. Number (7) ..Huh? If it runs underground ? Geeze. O.K, How ‘bout this. When it floods his track will have to be pumped out. I would be really interested to know just how long a run it is to get his system back up to altitude..
Number (8).Cabintaxi? CABINTAXI? “Somewhat more people preferred riding above the guideway than below” in giant square boxes on giant concrete roadways in the 70s? Sheesh. Number (9) He gives that one (not having the track in the way) to the hanging vehicle, but only as an advantage in buildings. He never mentions that the same applies everywhere else as well. Finally number (10) mentions that he has a successful plow and a ditch to push stuff (that falls into his track) into. I think he could at least say that he gives this one to the hanging camp.

Let me add a number (11) to the list. If you are in a hilly city, like San Francisco, and you are going down a hill and there is a turn at the bottom, the non-hanging vehicle will throw the passengers right out of their seats, unless it goes very, very slowly. In fact it has not been demonstrated, (to me at least) that bottom-mounted vehicles are capable of serving hilly cities at all. Not once is the self-leveling quality of hanging vehicles mentioned. Although I touched on it before, I think it deserves a number (12) to note that track banking is speed specific, and therefore inexact. Not so self-banking, hanging vehicles. Also previously mentioned but worthy of it’s own number (13) is the need for expensive raised stations with elevators, Too few stations take away a huge advantage of PRT, that is the “point-to-point” aspect. They cannot come down to earth because if they did they would either tip people out of their seats or block a huge swath of real estate on a gradual descent. That would open up the possibility of vandals climbing, painting, or putting stuff in the slot. Heck, if he would add a number just to make a point about what would happen to PRT underground, we should be able to call this number(14). Stuff in the crack. If the track isn’t above the trees, then leaves, seeds, etc will fall in the crack. Add a little rain and time and it will be a planter full of soil and rust. If it ever is at ground level, there’s a lot more than leaves to worry about. There’s garbage, and that a five inch crack is big enough to fall into up to the thigh. That’s point (15),

I guess my main gripe is that he never mentions the major drawbacks to his system (no slopes, major problems at ground level, and consequently expensive (and therefore less numerous) raised, elevator equipped stations. He keeps using the term “all else being equal.” All else is not equal. Raised stations may not be a big deal downtown, but they render the whole system impossible to scale outward into the suburbs, where station traffic would be less but the benefit of car miles eliminated would be more. There is already a system out there that can move people around downtown but is too expensive to scale. It’s called light rail. In all fairness, however, he’s locked in. Once money is raised, it’s pretty hard to tell your investors that it would be better to start from scratch. It is also a fact that, from a business point of view, you don’t want to shellshock your customers with too many new ideas. I just hope he makes his track easily upgradeable.

Saturday, May 2, 2009

31> Fired Up!

I am all fired up about the wheel-motors from PML. They are back-up battery ready, very powerful, light, efficient, recapture energy upon braking. They are easily capable of high speeds or very steep slopes.

Here is a system I designed to do just that. The smaller diameter of the gear reduces the travel of the wheel while increasing pulling torque. The PLM wheel motors are, in this way, easily capable of a thousand lbs (453 kg) of lift each, while still being able to achieve horizontal speeds in excess of 50 mph (80 k/h)

This system works because the wheels can be independently disengaged (powered down) during the transition to gear/tire drive or held to an RPM, which is consistent with the vehicle speed, rather than the speed of the other wheels. Therefore one wheel (which is gear engaged) can be rotating at a different RPM than a wheel whose tire is still engaged. The final effect is the same as motor, transmission and clutch, all with no moving parts except the wheels.