PRT: Combing the efficiency of cars with the convenience of transit.

Oh, wait.

by BeyondDC on Mar 12, 2010 12:24 pm • link • report

The theoretical peak is interesting. Most assume speed of the cars only. That means 100% efficient boarding. I could do the same for a highway, assume there's no reason to break, but that's not realistic. Like a highway, once you cross a certain threshold your throughput drops dramatically. Heathrow and WV look appealing since they are not near capacity, this means slow boarding can be absorbed into the system w/o any adverse affects.

by m on Mar 12, 2010 12:41 pm • link • report

The Morgantown PRT is really PRT, its essentially one loop, with car that simply skip some stops. It is also lightly used, not used for regular communiting, and had long periods of scheduled down time (university breaks, etc) that allow for maintenance.

A PRT at Tysons would be totally different from what you have in Morgantown.

PRT at Tysons would, in essence, be a large investment in a system to be used for one of the largest job centers in the country, that has never been proved to work in the US, except for on a college campus.

by urbaner on Mar 12, 2010 12:46 pm • link • report

The computer generated imagery is fun to look at. That's about all I take from this.

by Matt Glazewski on Mar 12, 2010 12:47 pm • link • report

@Matt

Agreed. This reminds me of those "cars of future" videos from the 1950s. Fun to look at, but I can't actually see it happening.

See also: http://www.youtube.com/watch?v=AEZjzsnPhnw

by Adam L on Mar 12, 2010 1:09 pm • link • report

My cynical view: Great idea. Except that DC/NOVA are not known for their forward-thinking. We'd had a metroline to Dulles and BWI 25 years ago if they did. I can already see the jealous protest of SW-VA tobacco farmers.

by Jasper on Mar 12, 2010 1:09 pm • link • report

Do people have to podpool during rush hour? HOP-2?

by JM on Mar 12, 2010 1:38 pm • link • report

Well, now I understand PRT. Before, the best I could muster was to think of it as "like cars, except it's transit", which didn't make much sense. Between the photo and the map, now I get it: it's like an elevator, but scaled up.

I don't know if it's feasible (including politically), but it's an interesting thought. For the required investment, given Tysons' population, seems like you might want something with higher throughput if you're going to make more than a small dent in driving.

by Gavin on Mar 12, 2010 1:42 pm • link • report

BeyondDC nails it: PRT is probably one of the dumbest concepts out there. That's why it doesn't exist anywhere in real form.

by MLD on Mar 12, 2010 1:56 pm • link • report

For more on Personal Rapid Transit (videos, links, studies): http://www.prtstrategies.com.

by PRT Strategies on Mar 12, 2010 2:00 pm • link • report

Question: How could such a system have the capacity necessary to make its investment worthwhile? I say clear out the cars and dedicate space for buses on the street. That could be done more quickly and cost-effectively than building elevated guideways all over the place. That brings us back to our earlier debate about the aesthetics of elevated structures...

by Matthias on Mar 12, 2010 2:05 pm • link • report

I'm gonna be harsh in saying this in public, but PRT is a Joke>.

It's expensive, has low capacity, and is technically infeasible. What's not to like?

It's just another obfuscation tactic that the Highway Lobby tries to use to kill viable transit projects. We should ignore it. If it's such a good idea, why are there no fully functioning city-wide examples of it in the world despite the concept being around since the 1950's?

by Cavan on Mar 12, 2010 2:05 pm • link • report

Big problem is that there is only one lane in one direction.

Driving, walking & waiting for a bus may all actually take less time than getting on the PRT and riding it all the way around the loop which could be 8 10 or 15 blocks when a person might only want to go 5 blocks or say 4 blocks the opposite way the PRT travels.

by kk on Mar 12, 2010 2:18 pm • link • report

The people who bash PRT as fantasy are completely ignorant of reality. PRT is being built in Masdar City as we speak, where it will serve as the sole means of mechanized transport (read: NO CARS). Masdar is an incredibly ambitious project involving some of the most respected engineers and city planners in the world (CH2M Hill, Foster & Partners).

It is also being implemented at Heathrow airport (pilot system to open this year) and is planned for at least half a dozen other cities over the next few years.

Why is PRT being built? Because it is more efficient than any form of transportation (other than walking or cycling). Because it is more convenient, safe, available and accessible than any form of public transit. And because the technology is available and developed TODAY -- at least 3 vendors have safety-approved, ready-to-deploy systems.

Detractors need to pull their heads out of the sand and open their eyes (and minds) to this new and promising technology. It's not a panacea by any means, but it is a viable piece of the transit puzzle.

by Mike C on Mar 12, 2010 3:20 pm • link • report

The realities of PRT are difficult to determine because different vendors have differing systems with varying capabilities. Studies we have done show PRT generally carries more people than light rail for less cost. Everyone gets a seat and there is little or no waiting. Trips are non-stop. We are not associated with any PRT vendor and are the only professional consultancy of engineers and planners specializing in PRT. To learn more about PRT visit www.prtconsulting.com.

by Peter Muller on Mar 12, 2010 3:36 pm • link • report

@ Mike

How exactly is it more efficient ? Please list ways how so.

Do the pods cover all parts of the city.

Do they take the shortest route to anywhere.

Do they take the fastest route.

Can this not become backed up if there are millions of people in the city.

What happens if one breaks down and is blocking the roadway.

What happens in a black out if a city is dependent on these

Is there a Ambulance, Firetruck and Police car version of pods otherwise there will be cars in the city.

The version of PRT depicted in Masdar is different than what is shown in depictings for other countries.

These are on the ground and arent built like small onecar lightrail systems. There is no track sense the path is the street.

How is there different than a automated car which drives itself like we have all seen in movies.

The city is being built from the ground up so therefore you are making a decision to move there and accept it, rather than you living somewhere and something is built after the people arrive.

The place may be car free but will it be truck free those pods can not accommodate furniture, equipment, stoves, refrigerators, pods (how will they get to the city).

Unless they plan on building a freight train version or building a freight train line to the city; there are many things missing from this argument.

by kk on Mar 12, 2010 4:26 pm • link • report

Mike C:

Stats or GTFO.

by Jewdishoowary Square on Mar 12, 2010 4:35 pm • link • report

There is lots of information, historical and current, about PRT (also know as PodCars) at http://faculty.washington.edu/jbs/itrans/prtquick.htm There are three market-ready systems in the world, several more that are being developed. Links to details for ULTra PRT, Vectus PRT and 2getthere PRT are provided at http://faculty.washington.edu/jbs/itrans/techtable.htm
The big opportunity (probably lost by now) is to use PRT as a circulator system and a feeder/distributor to METRO, thus enabling METRO to bypass central Tysons saving a ton of money but not affecting performance by much. Everyone should also take a look at a PP presentation by Booz-Allen that shows how PRT could be used at all METRO stations along the DC-Dulles METRO line at: http://faculty.washington.edu/jbs/itrans/big/DullesPRT.ppt

by jasper on Mar 12, 2010 5:16 pm • link • report

While I was in college, KDOT hired a group of architecture students to envision and render what one of these systems would look like on an elevated track though out our campus. I reviewed all of the systems, the proposed track structures, and the "claims" by the companies pitching the PRT. I was actually impressed by the system and its capabilities.

If you read the technical aspects of the system, they are not diver-less cars. They are essentially an elevator on a horizontal track. The command and control mechanism works in a similar fashion to the priority elevators installed in the WTC 7 building. The cars are very simple, and if any faults are detected they are directed to "garages" for maintenance. There is even a function to reject cars if someone has an accident in them. They were not widely installed after Morgantown because the available computing technology to manage the system did not exist yet. Some of the concept cars have a built in battery to guide the car to the nearest station in the event of a prolonged outage (or emergency).

We envisioned that the overhead tracks be integrated with utilities, road lighting systems, and other street furniture. I think that if anyone were to design a system for Tysons- installing the system along major thoroughfares would be scale appropriate for the area.

And, I don't see these systems as a replacement of light rail; I firmly believe that they are designed to complement rail and bus lines and offer developers a unique opportunity to spend a relatively small amount of money to link properties to the silver line.

Good discussion!

Joel

by Joel R. on Mar 12, 2010 5:19 pm • link • report

Look, if PRT proponents want to be taken seriously, they need to stop showing us silly proposals that suggest we ought to build elevated rail lines above every street in the city, and start figuring out how to integrate the idea into our existing city infrastructure. Infrastructure is expensive. Elevated infrastructure even more so. Nobody wants to abandon their existing infrastructure to build an entirely new duplicate elevated version. That's stupid, and it's why PRT is stupid.

The reason we all know PRT is pie-in-the-sky nonsense is that PRT proponents are so hung up on the futuristic renderings, they aren't thinking about actual implementation alternatives. For example, a public bike-sharing system that makes use of bike lanes and cycle tracks is a PRT system in almost every definition of the term. That's something lots of people could support, and indeed are supporting. If PRT advocates latched on, they could claim it as proof of concept. Unfortunately, nobody in the PRT world wants to because low-tech bikes on existing surface streets isn't kEwL enough. It IzN't LiEK, tOtaLLy ExTEmE tO thE MaXXX!

Show me a proposal for taxicabs on a series of HOV lanes, and I'll buy that as a serious idea for omething that could theoretically be called "PRT", with potentially practical applications.

Show me a proposal for completely unnecessary elevated lines all over everywhere, and I'm sorry, but it just ain't going to happen. It's a waste of money, and everybody knows it.

by BeyondDC on Mar 12, 2010 5:23 pm • link • report

Use taxis and bikes on highly congested roadways in Tysons? Sounds delightful. Elevated guideways are not fantasies and they are not needed "everywhere" - which not be safe, secure, able to enjoy the view and get to where you need to be quickly without stopping.

by jasper on Mar 12, 2010 6:02 pm • link • report

BeyondDC exhibits exactly the kind of mindless anti-PRT bigotry that prevents real discussion on the merits and possibilities of this technology. He clearly doesn't know what he's talking about.

See part 4 of this series for a more rational criticism of PRT. I've already commented on that thread, because obviously the CRITIC who wrote that piece it actually READ about PRT and understands that it deserves a real discussion, not mindless smears. BeyondDC and others are not critics or skeptics, they're ignorant blowhards who don't even bother to read up on the systems they're smearing.

by Mike C on Mar 12, 2010 10:09 pm • link • report

The biggest "PRT" in use is in the harbour of Rotterdam! Since 1993 they use "Agv" to transport the containers in one of the biggest harbours of the world!
http://en.wikipedia.org/wiki/Automated_guided_vehicle
http://www.youtube.com/watch?v=2VlBCJhwxXE

"Prt" is underneath the same, but made comfortable for human use!
"atv"'s are also used in factoris all over the world!
So saying "prt" is untested and unfeasable is deniïng the facts!
It's already around for years, but you just did not see it because it looked different!
It's like cars and busses! They look different, but are basicly the same!

by jc on Mar 13, 2010 9:16 am • link • report

What the dogmatically faithful PRT True Believers call "anti-PRT bigotry", the rest of us call "common sense".

PRT doesn't work because in order to make it work, you have to build an entirely new infrastructure over just about every street. If you limit it to drastically less than every street, then that's not a true PRT. It's a paradox that cannot be solved without abandoning the silly notion that everything has to be elevated.

by BeyondDC on Mar 13, 2010 11:33 am • link • report

I wonder if Beyond DC has ever looked at some illustrative
PRT networks since his belief that there would be an elevated guideway on every street is based on his very faulty common sense. Typically, PRT guideways would be spaced about 1/2 mile apart, with stations about 1/2 mile apart. Some walking would be required in some cases, in others the station might be adjacent to or in a building which is the desired destination. Lots of PRT network layouts for various locations around the world are illustrated at: http://faculty.washington.edu/jbs/itrans/itrans34.htm
True PRT does involve some walking and would have to recognize that Tysons doesn't currently offer much in the way of pedestrian amenities at present - but that can be fixed. In some cases, PRT can also run at grade or in a shallow tunnel, if need be. How about some bringing some informed common sense to the discussion?

by jasper on Mar 13, 2010 12:33 pm • link • report

@jasper,

Because, as you acknowledge, you'll have to fix Tyson's walking environment anyway. And once you do that, then the 'last mile' problem is substantially eliminated.

PRT can be useful in a situation where the built environment is designed around the transit system (see Masdar), or in a campus-like setting where you need to link various pods of development that can't otherwise be easily linked (see Airports).

That's just applying the technology and the concept to reality. The operation and implementation of such a system are a totally different problem. We don't currently have a fully operating system of true PRT anywhere in the world. The cost estimates pushed by PRT advocates don't pass the smell test, and shouldn't be considered at all until proven.

by Alex B. on Mar 13, 2010 3:04 pm • link • report

I'd like to see an estimate as to the how and cost of "fixing" the pedestrian (walking) environment in the Tyson's area. How far would the average walk have to be with only four MASS TRANSIT stations to exit from. It's usually not pleasant to walk in locations where you have lots of cars spewing their exhaust in you face, no matter hom many bushes and flower beds you plant and have to keep paying to maintain. Also, let's make it the first and last 1/2 mile where the average walk distance is more like 1/4th mile.

If you like to experience bad smells, I recommend the vast cost overruns that have been experienced with all forms of "proven" MASS TRANSIT, aka as "big box" transit.

I doubt that you have seen the detailed,itemized cost estimates that have been prepared by some vendors, with the participation of companies that would manufacture components. Generally, they are not available to the public from private companies unless and until there is a serious effort to consider a project by a potential buyer. If you a potential buyer, you get this information and can check it out yourself or with the help of estimators of your choice, before you sign a contract.

And, it isn't the advocates that are "pushing" cost estimates, they simply repeat what the vendors are stating for public consumption. And,don't forget the cost of construction dispruption that always comes with Big Box" transit projects, including utility relocations and lots of pain for retailers.

by jasper on Mar 13, 2010 5:59 pm • link • report

Lines spaced 1/2 mile apart isn't true PRT. It's typical transit, just with a higher frequency of lower capacity vehicles (and of course, needless elevation when transit lanes on surface streets would do the same job).

If the PRT organizations out there are abandoning the concept of true PRT in favor of concepts with more infrequent lines, that is simply further proof that the idea of a true "last mile" PRT doesn't work. When even the PRT activists admit the only way to make PRT work is to turn it into normal transit, that's a pretty good indication that the idea lacks merit.

On the other hand, as I have already said, there could very well be potentially viable applications of PRT-like systems being applied to bike, taxi, or even bus services if the PRT crowd got over the nonsense idea that PRT has to be a new mode.

by BeyondDC on Mar 15, 2010 6:18 pm • link • report

What is the source of your definition of "true" PRT? For a couple of decades, there has been general agreement about the use of 1/2 mile spacing of guideway providing a maximum to/from walk of 1/4 mile on average - many would be shorter.
The current TOD craze also uses a walkable area of 1/4th mile radius around a MASS TRANSIT station. There are a number of ways that have been discussed for assisting those who prefer not to walk to make the journey to/from a nearby PRT station. It is generally held that there would not be more than 1-2 parking spaces provided at or nearby the station, primarily for maintenance and security personnel, as needed. Some stations would be located adjacent to or within desired destinations. The idea of putting more bikes, buses and taxis on the already badly congested roadways of Tysons is unrealistic and undesirable. Needless elevation? Certainly not, in a poorly designed and developed venue like Tysons.

by jasper on Mar 15, 2010 7:04 pm • link • report

Much has been said here about capacity. When I first learned about PRT, some years ago, I wondered the same thing. I now have a reasonable amount of experience with a simulator that works with the following features/handicaps:

1. Loops flow one way.
2. Loading and unloading time is a constant 8 seconds (each phase, or 16 seconds combined).
3. PRT stops (all off the main line) always have five berths (though in some design approaches, stops in low-traffic areas may have a minimum one or two berths, allowing for very small "station" footprints).
4. Maximum speed of cars is 26 MPH (although most PRT system designs can support up to 30-40 mph).
5. Headway (distance between cars) is 2 seconds (although most proposed PRT systems claim the ability to operate with headways of 1.0 seconds or below).
6. There are 9 stops (stations) and 142 cars in the system.
7. The PRT stops are looped together by 8 miles of guideway (exclusive of exits and the onramps for the offline stations).

All of these parameters are fairly conservative. If you wish, you can take the 16 second load/unload cycle to be average, assuming that some passengers board or disembark more quickly, others not so much. Eight seconds is roughly about the length of time an elevator in a busy office building might wait for you before closing its doors.

Anyway, after running the simulation for 282 simulated hours (more than 11 simulated days, which I did while writing this, as the simulator can execute at 1000x real-time), we can see the following results:

System throughput: 254,937 trips
Average System throughput per hour: 904 trips
Average systemwide wait for service: 6 seconds
Maximum wait for service at any station, under worst conditions of system stress and high demand: 4 min, 44 sec.

I hasten to add that this system was not optimized for station placement or system topology in any way. If we assume average automobile occupancy of 1.1 per PRT trip, then almost 1000 people can be served per hour by this very modest system. Better layout of the system, more stops to spread the demand load, higher speeds, and shorter headways can markedly improve the performance of this example system. But without them, the performance is sufficient to have a significant effect on street traffic, fuel consumption, GHG emissions, and accident statistics.

I did not write the simulator, by the way, though I created the rough-draft PRT system layout and chose the parameters mentioned above. Still, I have spent enough time with it to believe that it fairly realistically depicts how an actual PRT system might behave. And I am encouraged that the often stated doubts about system capacity and throughput, vehicle passenger capacity, and even the frequent criticism of "one-way" guideways, are just bogeymen.

by James Anderson Merritt on Mar 16, 2010 2:17 am • link • report

A comment above doubted cost estimates for PRT systems. Last figures I saw out of Heathrow equated to about $15M per mile of guideway (including rolling stock, I believe). A final accounting of the project may bring surprises, one never knows, but the reports of actual project costs have been fairly steady and consistent for some time. If that number holds, a system like the 9-stop, 8-mile PRT network I mentioned above would cost $120M. Is that too much for a system of this class? At $2 for one-way fare, under the simulated patronage, this system could make $15,768,000 per year from the farebox alone: That's at least $315.34M over 20 years.

Clearly, there are a great many "ifs" and details that could make the scenario brighter or gloomier. For instance, Heathrow's construction didn't include expense for acquiring right-of-way. This could be a deal-breaker in some areas, although PRT's "footprint" and right-of-way requirements would be fairly minimal -- much less than those necessary for a conventional road or light-rail track, assuming that the PRT operated above-grade. The placement of stops and the "look and feel" of the vehicles would combine with the average and maximum wait-times, and average and maximum trip times, and fare rate, to influence people's decisions about whether to choose PRT over other means of travel. But I think a very reasonable case can be made for PRT's ability to be financially self-sufficient. We owe it to ourselves to look more closely at the possibility before dismissing it.

To the person who wondered about PRT emergency vehicles (police cars, ambulances, etc.), you need to understand that PRT will not, in general, or anytime soon, REPLACE automotive vehicles. Even the people who like and use PRT will sometimes need a car or truck, van or bus, to transport larger groups together, to move cargo, to respond to emergencies, etc. We will thus also still need roads. BUT, roads can be made less crowded and safer, the more that people use PRT for their routine travel in their local areas. They also may not need to be so wide or have so many lanes. Not everyone will need to own or drive their own vehicles -- when they do need an autonomous set of wheels, they can rent them temporarily. The people who do still need to use automotive vehicles routinely will find that their routes are much less impeded -- cargo will move more quickly, response to emergencies can be more rapid, and fuel efficiency will improve as people are less often stuck and stopped in the kind of traffic that vexes us today. PRT's proper goal, in my opinion, is NOT to replace or displace the automobile, but to be a viable alternative that is sufficiently attractive to a large enough group of regular and occasional riders, as to be economically self-sufficient.

Frankly, if a PRT system can't pay its own way, I am not interested in it, as much as I would like to ride in one, someday. I'm excited about PRT because it is the first transit approach I have ever seen that offers most of the attractions of a car, without many of the car's significant drawbacks, and also appears to have the potential for self-sufficiency. Some people seem ready to dismiss the PRT idea out of hand, before finding out whether PRT has a realistic chance of fulfilling its promise. I am not among them.

by James Anderson Merritt on Mar 16, 2010 3:12 am • link • report

kk asked what happens if there is a breakdown and a vehicle blocks the guideway. The short answer is, "it depends." A more longish answer:

1. If the vehicle simply quits but can still roll, another vehicle (containing passengers or not) can push it to the nearest stop or maintenance depot.

2. If the vehicle cannot be moved and simply blocks the guideway, then other traffic can be rerouted to avoid it. A well-designed PRT system is a collection of interlocking loops that provide alternative ways to get to any point in the system.

3. Vehicles that are "trapped" behind a guideway blockage (past the last possible point of diversion) can be cleared of passengers by emergency vehicles from the roadway. It is anticipated that this service will be needed very rarely, and only for the occasional individual or for relatively small groups.

There may be other ways to deal with blockages and vehicle malfunctions, but these three immediately spring to mind as having been well-pondered over the years.

by James Anderson Merritt on Mar 16, 2010 3:43 am • link • report

One wonders what simulation program you used? What did you do about the time-specific demand at the stations? Was it the same at every station? What did you do about the empty vehicle redistribution problem? Did you operate the system 24/7 (around the clock)? How did you "stress" the system? Did you stress it to a breakdown condition? There are a large number of performance measures available from some simulation programs. For example, see: http://faculty.washington.edu/jbs/itrans/ingsim.htm for a simulation of a city-wide network in Gothenburg, Sweden. A number of other simulation programs are described at: http://faculty.washington.edu/jbs/itrans/simu.htm Your results are interesting but without more detail, hard to intepret. Did you use multiple storage depots, sized and located optimally? Was ride-sharing permitted? Did you use a traffic management strategy to route empty vehicles to certain stations based on a history of repetitive patterns of use? I'd like to see more details.

by jasper on Mar 16, 2010 12:16 pm • link • report

It would only work if you eliminated the entire concept of a guideway and just invented a robot taxi that's street legal.

by Steven on Mar 16, 2010 2:47 pm • link • report

Jasper: I used the Hermes simulator (http://students.ceid.upatras.gr/~xithalis/simulation_en.html), primarily for the ease with which it allows you to create a layout, set parameters, and see something work against a backdrop of a street map or satellite photo of the intended service area. It is not what transit experts would call an "engineering grade" simulator, and I would prefer it had several additional features or allowed certain customizations that it presently does not provide, but, as I said above, it models key PRT behavior quite well enough to encourage me and pour a lot of water on the bloviation of certain uninformed but nonetheless vocal and ubiquitous skeptics/critics I have encountered over the years.

You ask if anything was "optimized." Far from it. I took a layout that had been circulating around PRT-friendly groups in my town for years, and created a "rough draft" system that was intended just to create an interesting animation that illustrates the travel of PRT cars around that proposed route. I was very surprised to see the performance figures, and also encouraged because they seemed so impressive without me having made any efforts to optimize the system plan.

Hermes deals with the empty car redistribution problem by automatically sending cars where needed, either from stations where they are currently idle, or from strategically located depots. The depots in my particular system design are not as optimally located as they might be, but still, the system works well enough. I ran the system 24 (simulated) hours a day for periods up to several (simulated) months and got much the same results as I did for the 11-day period I ran while writing the original posting above. I was especially impressed to see that none of the simulations executed so far have resulted in a single "wave-off": the failure of a passenger to reach his destination because system congestion and/or backup at stops prevented his vehicle from ending the trip at the desired stop.

There are provisions in Hermes for varying demand by time and location; for my purposes, I was happy to use the random demand that the simulator generates by default. My local PRT interest group is acquiring real-world demand and population data for our region, and coming up with a "proper" layout of stops and guideway. We will feed that into Hermes later and see how the "second-generation" model performs. I am particularly interested to see how it does when faced with our known rush hours in our known high-traffic areas, and whether any "wave-offs" or congestion-related problems will (finally) occur.

My initial goal here was not to model a PRT system down to high-resolution realism -- that's the job of the engineering-grade simulators that would be used in an actual implementation project -- but to constrain claims on both the pro and con side of the debate to a realistic ballpark, and to give regular people a fair idea of how a PRT system could work and benefit them. People have been shooting from the hip and pulling opinions about PRT out of their nether regions for years. Testing ideas against even a consumer-class simulator such as Hermes -- which permits quick reconfiguration to allow for examination of alternative system layouts and demand scenarios -- helps to keep the discussion and expectations in the range of the possible.

by James Anderson Merritt on Mar 16, 2010 3:08 pm • link • report

If you don't like transit systems that "can't pay their way", what possible choices are available? I don't think any exist. PRT has the possibiltiy of making a profit or requiring a small subsidy, if it is deployed correctly so that it can provide feeder/distributor, circulation and goods movement services throughout the day. Keeping it busy is the goal. It can have a variable fare structure that can be easily customized to fit a variety of situations. Fares might be for either the vehicle (with one or more riders) or for each individual and be able to recognize special cases with the use of a variety of smart cards. Movement of goods can be timed to not interfer with the major passenger flows. In some cases, solar arrays can be used to provide power to various components of the system.

I'm glad to hear you used Hermes. However, I still wonder how you handled the demand at the stations. The Hermes simulation results I've seen have been derived from a uniform distribution of demand. It's well known that a PRT system that serves a many-to-many origin-destination input will perform quite well as compared to a many-to-few or many-to-one O/D flow table. Unfortunately, it's not that easy to find many-to-many flow patterns in real cities, sue to the aggregation of destinations in a few locations. One of the reasons why you didn't get any wave-offs might be that the demand levels you used didn't put much stress on the system. Crank up the demand and see what's possible - like a bridge engineer stressing his bridge design to find a load that results in a failure.

by jasper on Mar 16, 2010 8:20 pm • link • report

Jasper wrote: "Crank up the demand and see what's possible - like a bridge engineer stressing his bridge design to find a load that results in a failure."

We look forward to doing that just for fun when we have time. But again, stressing to failure is not our object at this moment. Rather, it is trying to see whether pursuing the concept to greater depth is worth committing any more resources. So far, the answer seems to be "yes," but the true proof will be when we plug in the real-world demand data. So far, using Hermes' random, even pattern of demand shows that a modest local system has enough capacity to noticeably ameliorate some horrendous traffic bottlenecks that we have in our town. If stress tests or system layout optimization would lead to demonstrations of even GREATER capacity, that would be gravy.

I agree that keeping the system busy is the goal. We haven't explored the possibilities for freight, but there has been the idea of a "mail car," which could circulate through the system, parking here and there and acting as a receptacle for mail, ultimately to return to the main post office.

by James Anderson Merritt on Mar 16, 2010 11:13 pm • link • report