Sunday, April 4, 2010

80> Twisted

I guess I have come up with a solution, of sorts, to the problem I posed in last week’s post. By introducing a rotating joint where the swing arm attaches to the cab, the cab can be pivoted sideways. This gives the clearance required for vertical travel. It also opens up some interesting station design options, such as the closely spaced front boarding shown in this video for Monic PRT.

The picture above shows the indoor station problem to scale. The rail here is fairly large, (nearly 36” tall) and is the high-speed design shown in post 74. The vehicle is 63” tall at the pivot point. This cannot be reduced much without making the seats too low or sacrificing headroom. (No, the rail is not part of the back wall; the viewing angle just makes it appear that way...)

The ceiling as shown is 10’ 9”. Luckily, most modern buildings have more distance than this between floors. That makes the bottom of the track at 7’9”, barely within reach of the average adult. Because being able to reach it at all is a bit troubling, work continues on trying to find the best way to shave a few inches off of that 36” dimension. 
In the second illustration the cab has been turned sideways to the track in preparation for descent and in the last it is shown on a vertical track section. Note that the swing arm must be at least half of the width of the cab, but not so long as to push the overall height of the system higher than is necessary to keep track out of easy reach, lest the system be too tall to fit between the floors of most buildings. 

One thing I would like to accomplish with these designs is to create a system architecture that enables a business model that is not as reliant on busy stations. I understand that previous designers have had to keep in mind that “the squeaky wheel gets the grease,” so any initial system is likely to be for a very busy area. Also, in the beginning, limited funding will mean that PRT will have to prove itself with a minimum of both track and stations. Still, PRT’s main strength lies in concept of point-to-point travel, and that means lots of stations. Trying to do otherwise is like having a taxi service that only goes to and from a few locations. We already have that; they’re called shuttles, and are most efficient when transporting larger groups.

Reducing the cost of the stations is a main factor favoring hanging vehicles over bottom-supported designs, which require extensive means to keep people away from the track, like elevators, gates, fences, etc. Cheaper stations will eventually pay off in higher ridership. Can you imagine, for instance, public buses trying to operate with two thirds of the bus stops removed? Who would want to walk that far, both before and after the ride, and presumably on the return trip as well? PRT is no different. It is unavoidable that initially PRT will have to start in an environment where shuttles would be competitive, but it is unwise to create a system architecture that is only economically viable in these situations. This is particularly true in many U.S. cities, where activities like shopping and entertainment are often done very far from the city center. By the way, the larger track size shown is fully compatible with larger group (GRT) vehicles, if it can be shown that they would be more effective in certain routes. The vertical or steep slope travel capability, however, is PRT only, and aimed primarily at situations where a small footprint is needed, yet the ridership isn’t sufficient to justify an elevator equipped station. Sharing space with a bus stop comes to mind. 

Finally, I have to acknowledge the differences with European hanging designs, which have no swing-arm at all, although they have similar track heights, because they tend to be taller, walk-in style vehicles. A quick “walking view” tour in Google Maps of various European city centers reveals huge masses of pedestrians compared to the U.S… many, many times more. I can certainly see that a lower speed, inner-city centric approach could make a lot of sense there. While we struggle with “urban renewal” projects here in the U.S., it appears that they’ve “been there, done that,” in Europe, perhaps hundreds of years ago! (Some of the oldest U.S. cities seem to have more vibrant downtowns as well, and being constrained by water seems to help somewhat.)  The whole structure of many American cities, especially in the fast growing “Sunbelt”, is about growth along freeways, giving the cities long tentacles of urbanization. The designs I have shown reflect this landscape. 


chronokun said...

I really like this vertical lifting idea and in-building stations, it's amazing to think that this system has a footprint only a little larger than an elevator and could bring this point-to-point transport right to the door steps of people living in high-rise apartment buildings so they don't even need to take an elevator to the lobby before they begin their jorney, super cool xD

Bruce said...

Your solution looks more elegant than the S.A.T. project:

Anonymous said...

Elevated PRT stations are not JUST an expense - they are an opportunity to locate small business facilities near people's dwellings

Dan said...

Dan the Blogger responds…

Hi, Chronocun…Nice to see a new face around here. xD Since I am trying to develop a comprehensive, flexible PRT system, instead of an iteration for a particular market, I’m pretty much free to dream up anything that seems reasonably practical. I don’t know about the high-rise idea though, because the elevators are already there and counter-balanced, but theoretically, at least, you are right. If PRT ever really takes off, who knows?

Thanks for the link, Bruce. That’s one I have not seen. I don’t really understand much about it, from the description. It sounds like it has both a central motor and individual motors. They are right about one thing though, imho, and that is the need to think vertically as well as horizontally. The 2D spreading of cities and suburbs is so energy inefficient that economics will increasingly force change. If you think about it, even freeways are just a 3D solution to a 2D problem, because they solve right-of-way issues with overpasses instead of stoplights. PRT has been likened to a horizontal elevator, and I think that’s how these folks attacked the problem…by making an elevator go sideways. (fifteen people, boxy shape) Obviously most PRT designs start as a vehicle first, but making PRT function as a vertical elevator is a reaction to the same problems they address.

I’m not sure I follow, Anonymous. I recognize that places where people aggregate is a natural place for a business, but I don’t see how being elevated helps. I also don’t know how the land ownership aspect would play out. Would the city be leasing some elevated station area, or some sheltered area below, or what? How much space are we talking about? What about utilities? What kind of business are we talking about? For that matter, I don’t know what kind of dwellings you refer to… Inner city or suburban? It’s an interesting concept, the idea of distributing from periodically placed centers. Mail distribution comes to mind…Anyway, I think elevated stations are the way to go in most instances where a steady flow of passengers is expected, and, yes, a raised platform does produce shelter of sorts below it.

akauppi said...

By the way, I am simply *amazed* at how much publicity there has been on PRT in March-April. Seems the hype curve is picking up:

I thought this will interest you. Sorry for being completely out of the discussion.

Bruce said...

I understand what Anonymous is saying. PRT stations can be a business opportunity, instead of a cost. I will upload some sketchups that indicate some of the possibilities, and come back with a link.

Meanwhile, if you really want to know about the technical details of the S.A.T. project, they're described in US patent #6431078, with lots of drawings. You can get the PDF from Google, thus:

afransen said...

Large PRT stations will be much like subway stations, which can support coffee shops, etc. But many PRT stops ought to be like bus stops, to help keep system costs low and that means a system capable of coming down to grade with minimal structure.

cmfseattle said...

what's inside the guideway that allows slopes so steep?

Dan said...

Sorry I’ve only been checking in every other day or so. I’ve got a lot on my plate besides PRT at the moment.
Thanks Akauppi, for the “heads up” on the news. I am glad Mr. Muller is giving a bit of airtime to something besides Ultra. The piece he did on station routing that pretty much made any rail based system sound unworthy of consideration. I can understand these guys wanting to concentrate on systems that are deployable now, and neither Skyweb nor Vectus are particularly flexible in this respect. Still, as this post shows, rail based systems could potentially do things that roadway based systems could never dream of. I’m flattered they posted my blog.

Bruce, I checked out the patent briefly. The claims are pretty weak, luckily, since they would otherwise cover almost all hanging PRT. I can tell the examiner made them put in a couple of key phrases that really undermine what they started with. It looks like I was right about it being and elevator first and a vehicle second.

I think the idea of making stations into separate revenue generators via sales of snacks and magazines, etc. is a pretty good idea, where it could apply. This could be part of the business model where such revenues could help sweeten the deal for either the PRT vendor or municipalities, and insofar as a raised station creates a walkable area where there was none before, that is essentially something for nothing. However, the space below has value as well, and is not free. If it is a public easement, which will usually be the case, there is little way to make it happen. In a city owned parking lot, where it could shade and shelter cars, it sounds like it could work.

Alfransen, Ditto. I agree.

Cmfseattle, there’s ‘nventin’ to do. I am trying to keep all options open, and there are quite a few. There’s externally powered vs. internally, and even both since I can imagine and externally powered system that would allow internally powered climbing for those vehicles so equipped. Since all vehicles should have an emergency mechanical brake, one option would be to replace whatever it clamps to with a moving cable or finned roller chain. (Notice that I have never included brakes? Now you know one reason why.) Then there is the old cog railroad technique, like I show in post 31. A stretched roller chain or two can even be used as a rack. (By the way, there are many exotic roller chain designs out there with flats, grippers, fins, pegs, etc. to choose from) Then there is V based friction engagement. Even a worm gear would work. Internal power can be complimented by external linear motors. The possibilities are almost endless. So far I am just leaving space.

akauppi said...

Chronokun. Please keep in mind it's not just that simple. There are security implications (which can be solved). Vehicles will also bring dust and/or snow or whatever from outside (which also can be solved).

I don't expect PRT to be used as elevators within buildings. Elevators are already very good (and clean) in that. But entrance to a building is no longer limited to "street level" and garages. New buildings or i.e. hotels that are modernized may take in people at the "rail grade level", with nicely integrated reception desk etc. It will be like a train station only smaller.

afransen said...

It's true that a major constraint in the design of tall buildings is elevator technology and the need to shuttle people from whatever height in the structure to ground level and back again. If a PRT station could be located mid-way up the structure, that could be reached by a guideway climbing the side of the building, this would help enormously with easing the proportion of floor space that must be devoted to elevator shafts. Since elevators must travel up and down along the same alignment, we are limited in how many vehicles can operate within a shaft to one, or with some jiggery-pokery a small handful. But a constant stream of vehicles can flow in one direction and out the other, occupying perhaps less cross-sectional area than two elevator shafts and it can even be outside the building envelope.

It has potential to improve the economics of vertical structures greatly.

chronokun said...

Those are very good points akauppi, I had already briefly considered the security concerns but they didn't seem a hard problem to solve and I suppose keeping snow and dust from being brought in wouldn't be either. Of course you're right that elevators are generally quite adequate although in some cases with larger skyscrapers being built a future vertical bottleneck doesn't seem impossible, already some designs make use of multi-level elevators and express elevators and such. Since each shaft takes floor space off every floor and can generally only host one elevator it would be nice to have an alternative that can be more versatile especially if buildings are to be built that are both tall and wide.

Anonymous said...

afransen. I think you are missing an essential point.

Limited horizontal mobility has caused the need for tall buildings. It has been easier to create vertical elevators than horizontal ones. Now, if PRTs improve the horizontal mobility, it makes 'flat' cities more attractive, again.

So ask why the buildings should be tall?

Anonymous said...

Hi Again, It's me - Anonymous.

Two things - first, the little discussion on expanding the utility of elevators by making them follow more closely the PRT Model highlights, to me at least, the weakness of calling a PRT system a "horizontal elevator".

I guess the idea was supposed to be "push a button, the door closes & it's automatic from there", but most people's experience of the elevators is:

1) Group transit - you ride with strangers.
2) Stops (constantly when you're late) to let others off & on.

A better analogy should be found, or just forget analogies altogether.

Second, back to the issue of PRT stations. An elevated station has room underneath it which could be used to provide convenience services for people in their neighborhoods. This could tie in with the power of PRT networks to transport goods, & not just people.

For example, you could purchase that new big screen TV on-line & your local Costco could ship it to you via PRT to your local station where a Mom & Pop delivery service could transport it the last quarter-mile.

Or you could pick up a DVD from the Redbox vending machine, or a quart of milk, etc.

You could drop off your recycling, which could be transported to a center on a PRT car designed to haul freight.

Etc, Etc Etc - there are many opportunities that I'm not even thinking of, I'm sure.

afransen said...

akauppi: the point is not that we should never have elevated stations, just that the system should not require elevated stations.

Whether or not the uses you propose would be successful seems like something that is a secondary consideration. The system design should not preclude these uses, nor should it make significant design compromises (like requiring elevated stations, which is a huge compromise).

Anonymous said...

One of the benefits of PRT is that the elevated guideway separates it from ground level motorized & pedestrian traffic.

The scheme of having a suspended car descend into the ground level space presents a real safety hazard to inattentive pedestrians & motorists, that would probably have to be countered with a system of rigid barriers - no more cheap "bus stops" - because who wants to be struck on the head by a 1200 lb podcar descending from the sky?

Bryan Williams said...

Wow, very cool designs. I think your designs and your blog show how we've only scratched the surface for this kind of system. Moving vertically and tracks that can move like that around corners I think more or less throws out the traditional transportation rule book.

Dan said...

Dan The Blogger weighs in-

Akuappi, This is a classic problem of urban growth. Every time you improve the transportation to an area, that area experiences growth until your transportation system is inadequate once again. I have to say though; I am all for building up, not outwards. Larger building size provides efficiencies in heating and cooling. If the activities of a tall building were spread out horizontally it would create a huge lifeless footprint. I believe in treading lightly on this earth whenever possible, and taller means more room for parks.

Anonymous, Thanks for bringing up the how bad that elevator analogy is. I agree. I should stop using it.

I agree with Alfransen’s comment about the elevated stations. This is particularly true in light of the fact that I am trying to create a flexible standard here, not a “preferred embodiment.” (as the patent guys call it) I want whoever uses these designs to be able to have a multitude of station choices. Never the less, it’s good to bring it up, because it raises all sorts of good and important questions. One is, “How many passengers per hour are we expecting from a typical station?” In many previous models routes that didn’t support large busy stations were simply regarded as routes that didn’t need to be built. At some point I want to really study this supposition. Is that really PRT’s “sweet-spot”? Or just what the vendors would prefer to offer?

As for the prospect of being struck on the head by a descending vehicle, a couple of points – First, this model presumes a very slow descent…slow enough to not cause injury. After all, we are only talking about the last few feet of the docking process. There can be auditory signals. There can be sensors. There can be “tilt” switches. There can be low, ramp accessible platforms. And yes, there can be fences or roped-off areas. I agree it is a challenge, but it is addressable.

I think it is important to be able to locate points of access wherever they might be used, without being restricted by a set station design. I do not mean to weigh in against elevators per se. I would like to design an elevator system designed specifically for low volume PRT that would draw electricity from the track and require minimal (if any) excavation. Again, this is not for areas of high pedestrian density where larger station sites are available. Many of the areas most in need already have had all available space dedicated to road widening, leaving only utility easements, which have, of course, buried utilities. My view is that being able to “sky-hook” passengers out of there, one way or another, should be an essential goal and every tool should be considered. It is not so much the elevator that is the problem; It’s blocking traffic, digging equipment, cement trucks, permits, inspections, etc.

Thanks for the kind words, Bryan!

Dan said...

Also, about the elevator thing, there is also the matter of freight or even industrial use, as well as vehicle maintenance. Vertical capability has potential advantages in situations other than passenger pick-up and drop-off.

qt said...

About the elevator analogy:

I seem to have seen it first from the JPod people, And they were using it in contrast to subways and other "mass transit." Their point involved ease of use, accessibility, and (relatively) short waiting times.

You're right, podcars* are better than elevators, but until we find a better example of ubiquity and "just get in" simplicity we may be stuck with it.
*(just helping the search engines find us, sorry)

an-148 said...

this post is a reply to my suggestions for pages 52 and 79 :-)
nice !!