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 www.prtnz.com 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.