Saturday, February 19, 2011

118> GM and Segway’s Unintentional Dual Mode Platform

As many of you know, I have never been a big fan of dual mode.  The problem is simple.  If a vehicle is light enough to be part of an effective elevated PRT system, it is too light to be a robust road vehicle.  Conversely, if it is sturdy and comfortable enough to not seem ridiculous as a car, it would require a track that would be unacceptably massive and costly.  You tend to either have a bad car or bad PRT or both. Yet if you thread the needle just right, they are off by tantalizingly little . Lithium based batteries, ever-shrinking computing power, carbon fiber technologies and miracle plastics are nudging things forward, but what is needed is something really dramatic.  Something to knock off half of the weight form the start. 

The other day I was thinking about all of this, or at least how to transport people that last mile.  I was considering bicycles, scooters, and Segways, and wishing for something that would have a roof to keep the rain out.   I was even considering what technology would be involved in matching PRT to a Segway, instead of the other way around.  I even have a picture to prove it.  

It was around then that I decided to do an image search for a rain-proof Segway, and I stumbled onto something that had passed beneath my radar when I first heard about it.  It is the EN-V concept car, which, as it turns out, which may well be the “best-yet” dual mode platform.  It is a joint venture between GM and Segway, and it does two things that really reduce the weight problem.  First of all, it runs on two wheels instead of four.  Roadworthy tires and wheels are heavy, after all, especially if you include durable shocks and springs.  This vehicle also lacks a mechanical steering wheel and all associated linkages.  Like the ULTra, it is self-navigating, or at least, “drive by wire.”  That brings up the intriguing notion of having the vehicle drive itself back to the station after dropping off a passenger.  The side-by-side, two-wheel arrangement enables steering without any pivot assembly, and also allows 360 degree rotation in place, something that might add considerable flexibility in station design.  

The relationship between the EN-V and PRT seems symbiotic: PRT can’t go the “last mile”, and the EN-V can’t go all that far.  The EN-V’s shortcomings in speed and battery life could be rectified by an electrified track.  Equally promising is that the EN-V weighs in at under 500 kg, and that is for a version with a much bigger battery and motor than would be required for dual mode use.  Also, as long-time readers well know, I have my doubts about how good of a PRT vehicle can be designed and constructed by any fledgling company without seriously deep pockets for R&D.  GM and Segway have dumped a lot of money and knowhow into this project.  They have based the vehicle on what they call the “Puma” platform, which is literally just that… a versatile, self-balancing platform slung between two wheels.   

I really think this combination deserves some serious consideration, more than I have time for within the context of a single post.  Look forward, therefore, to more on this subject in days to come.

Here are some related videos: This short clip shows the “Puma” platform without the passenger compartment. 
This second video shows a bare-bones version in action as well as a simulation of a city street designed for using the vehicle as an ULTra-like PRT.
The EN-V comes in three flavors, as shown in action in these vids.


akauppi said...

Heh, me again first here. Sorry guys - I get the updates as RSS and we're anyways 5-10 hours "ahead" of US. :)

The drivetrain animation is really nice - some innovative balance mechanics there.

As to Envy vs. PRT, the Chinese are thinking of making these things run autonomously within a city center. Shared vehicles, not owned. Or *all* vehicles in that particular area are autonomously guided, thus much easier to orchestrate and safer than manual + automated drives mixed (which I am doubtful will work, in less than 50 years).

So, essentially, they're making "PRT" on ground level. Which is fine. But I don't think getting a rail will give any added benefit to that concept. These are two alternatives, as far as I can see it. The "Chinese" way and the "Indian" way (because in India, I cannot imagine an area where manual driving of any kind would not be allowed).

Thus. Maybe there's something in there for PRT. But I consider it a friendly rival. Answering the same problems and most likely doing it quite fine without any "PRT" technology involved. To the passenger, such two systems won't be very different. It's automated movement from one place to the other. And the cabin sizes are pretty alike the rail-bound PRT's.

The way China is starting, it seems, is introducing electrical manually driven vehicles that can be upgrade to autonomous drive later. It's a clever strategy - I do hope it works for them. We simply cannot get China + SUVs and still think of saving the planet. :)

Andrew F said...

I agree that this is generally friendly to PRT, or that it fills a mostly non-competing niche. PRT is fast and can be long-range within the city. This system will be short-range and low-speed by virtue of the fact that it runs in a mixed ROW and uses a limited size battery.

China can't have two SUVs in every driveway, even if they wanted to. Beijing has already started restricting the number of new cars. They simply don't have the asphalt for 1.5 billion cars.

Lars Endre said...

Thanks for showing an alternative and starting a dual mode discussion, even though You were pricipally against it. The point of having the worst of two worlds is valid, but I don't think it is "big".

I am seeing this the other way around (so I am all for dual mode); both solving the last mile problem and to utilise existing designs (cars), sounds important for "actual-world" implementation of PRT.

One should also NOT underestimate people's want/possibility to own their vehicle.

The "last mile" vehicle should anyway be "PRT-small". SUV's are just a bad idea, and has always been. (Read on why electric cars have the same range today as they did 100 years ago!) Existing asphalt could gradually be designated to "PRT-on-road" vehicles, and the demands for these to be sturdy (and then heavy) dimished. I'm seeing a currently functioning electric car, but it's reach (and purpose) limited to - exactly - "the last mile" (0-20 kms). No need for 500 kgs of batteries (40?), and then suddenly possible to drive on (slim) tracks.

All that I need for "my model", is a guideway that will 1)take over control/prohibit manual driving and 2) charge-while-driving the vehicle.

THEN I would buy an electric "car"!

Dan said...

When I was in my twenties, it seemed like everyone lived in apartments, like me. Now I have had a house for 25 years and I don’t even know anyone who lives in an apartment. Most people in the US get a house once they decide to raise kids. Is this unusual in Europe?
I live in a very young and fast growing city. Here (although this is also pretty typical throughout the US) the typical commute involves a 5 minute trip to a freeway, “X” amount of time on the freeway, and another 5 minutes from the freeway exit to the destination. As the “X” variable increases, housing costs drop. You can live a lot better if you drive even 5 extra minutes per day. This even includes apartments. Is this unusual in Europe? Some times I get the feeling I am the only one here who doesn't live on a bus route...
As for developing countries, my travels in such places were all quite long ago, so I really don’t know how far these people commute, although it seems like places with fewer cars must have a lot of housing very close to town. But are stable job opportunities really so local that you can get there at golf cart speeds? Or is that all changing?
My interest in the EN-V would be for well under 5km trips. They still create interference (and are interfered with) at ground level after all. But with even short ranges a dualmode scheme greatly multiplies coverage per amount of track/stations. I would strip the EN-V down, with smaller battery and motor, and use the PRT as a high speed means to get the EN-V to within a couple of kilometers of the destination. They wouldn’t be doing the same function at all.
As for ownership and the weight issue, People here buy SUVs because they feel safer driving in them in the insanity that is modern traffic. People will always buy big vehicles, at least in this part of the world, because there will always be a need for vehicles for people with large families, and single individuals are free to buy them too. When the US government mandated (to the car makers) incremented fuel efficiency gains for the US auto fleet, everybody started buying big pick-ups. The SUV was developed as a “truck” and so it side-stepped those energy efficiency requirements.
In the US, at least, the heavier track that could support 1000kg loads has been rejected as too big, expensive and ugly. The attempt by Raytheon to build PRT in Cincinnati stands out as an example. (The final report by the city is available online somewhere) I don’t know, Lars, if you were implying that privately owned vehicles should be allowed on PRT track, but of course that opens all kinds of safety and reliability issues. I can’t see it. Not here, anyway. People will still want a private vehicle, but they shouldn’t need to drive it everywhere they go, and I don’t see mixing it up with PRT as being viable. If there was government funding with highway scale budgets, (and political will to match) then that would be something different. Maybe some countries in Europe are ready for that, but it is out of the question for the US.

Dan said...

My apologies to anyone to has been trying to post comments here. I don't know what is going on, but this is not the first time. Normally I get email copies of comments as well, I have one there from cmfseatle that I will attempt to repost post myself. I know sometimes people comment and nothing at all happens...
I guess maybe a free blog IS a little too good to be true...

Dan said...

Dan The Blogger attempts to repost cmfseattle's comment. Sorry if the links are not clickable. I suspect that sometimes that aggravates the problem.

Cincinnati was post-Raytheon.
Documents #11 and #12 are my favorites:
Vectus says their chassis is good for ~2,000 lbs.
They've plans for a 2-segment, articulated GRT vehicle.
From Uppsala to Suncheon City (PDF, 10 MB)

Thanks cmf! I had not seen that visual intrusion study. You know, one of the reasons for having a hanging design is because it can take slopes so readily. This enables very high track, (without equally high elevated stations) which is an option that I suspect many communities would demand. I think bottom supported PRT developers have missed the boat by not seeing this coming a mile away.

cmf-seattle said...

I think I may have been mistaken to call the Vectus GRT vehicle "articulated." It's likely just 2 chassis connected by a drawbar.

I think you're right about my post being full of links; some blog services have a threshold and just assume it's spam.

Lately, I've been swaying back to the suspended opinion, too: provided they'll fit, I think parabolic arches would work better than posts in a median. Also, I think dropping the floor as an emergency-evac method could double as a station elevator; sort of like how Anderson thought the Aerospace electromagnetic switch should have a mechanical back-up, which may as well be the primary switch.

So, the pod pulls up to a berth and the floor drops to street level inside a tube. At the bottom, doors on the tube slide open. May be a way to avoid the stairways requirement?

Just ideas [:

Dan said...

I’ll have to remind myself to go back to some of these ideas if I run out of material to post about, cmf… The floor dropping out idea is one that certainly deserves more attention than it can get at the end of a thread about something else… Part of the reason I haven’t dealt with the issue is that it is pretty hard to even discuss without good drawings of all of the options, and there are a great number of options indeed. Does just the floor drop or the whole cab? How do the doors swing? (Or are there no doors at all, just the dropping floor?

In the Flyway scenario,(sorry, blogger won't let me give you a clickable link - it's they never really make these judgment calls, and the bubbles and beams videos also allude to multiple means to deal with the boarding issue. I’m not sure there is a “right” way to do it, just lots of nearly equal choices. That raises the issue of how specific we want to get, and at what point. Is it better to commit to a design and foreclose the other options or leave them open, and live with a fuzzy picture of how the whole process might work?

One point about having the emergency evacuation and normal boarding being the same; The emergency evacuation could be designed much less robustly, since it won’t ever be used anyway. It also only needs to go down. (and not onto a freeway) Elevators that get used many times per hour, on the other hand...

Easier is the arch business because it’s a more discreet building block. The existence of medians, I suspect, is due to city planners’ recognition that today’s suburban boulevard might be tomorrow’s super highway. There is also usually a large amount of unseen utility infrastructure beneath there. I know in Houston there are storm sewers big enough to drive a midsize truck through, not to mention the largest gas, water, and septic sewer pipes. All of this makes me think medians are probably fairly universal worldwide, and so can be thought of as a constant that can be designed for, although they do fill with lanes of traffic over time, just when PRT is needed most. Where I live the routes with medians would be best served with two way track, and as such a “T” support seems best, so that the roads can be expanded without hindrance. But I say that in ignorance as to the maintenance requirements of all of that utility infrastructure. My guess is that it’s a decision best made locally, although dig-free support options would be useful.

Dan said...

Dan the Blogger has been doing a bit of research…

In regard to my earlier questions about commuting in countries other than the US, I went looking for some statistics on the matter. I found a website that gave me some clues. There is a lot of info there, so I’ll just point to it instead of giving all of the links. It is under the “statistics” tab. Under this heading one can choose “people” and that gives a further list with stats on things like home ownership. Under “transportation” are headings like “car ownership”. The statistics are graphed by country. One thing I found interesting was that people of English speaking countries have houses that are both significantly bigger and more highly taxed. That would tend to lead to suburban sprawl, because property taxes fall sharply farther from town, and apparently we like lots of room, relatively speaking. (like 20% more) Seems cultural.

I also looked, with Google maps, at a few European cities to sample the extent of highways in the urban/ suburban areas. They seemed not too much different than the US. It looks like many, if not most, people are indeed about 5 minutes from a highway. From the air, anyway, it looks like higher speed PRT “arteries” along such routes would find a good ridership, particularly if the vehicles had enough dual mode range to reach the whole area encircled by those highways.

qt said...

re: Private vehicles on the track, safety, and reliability,

I'm not sure how many issues it opens up. Presumably, the only thing the PRT operator is really worried about is whether the hookup point is in proper order--the battery and motor, for example, would be the owner's problem. (Given the honored position lawyers have in the US, of course...)

re: "stripped down" EN-V's,

I wonder how far you could strip them down. If the only thing they can do is stagger to the nearest PRT stop you'll have a hard time selling them, and not just because they're not SUV's.

You won't start out with a station every mile. That won't happen for a long time, in fact. If your "car" can't be used in the sparser areas, who'll want it?
Not all miles are created equal. A mile in Atlanta is likely to be a lot hillier than a mile in Houston, I suspect. The battery and motor capacity will need a fair amount of wiggle room.
Even when you've got a stop every mile in every direction, not everybody will want to ride the rail to the next station. A vehicle that'll cut the corner would be a real advantage.
Remember the "honey-do" run? What if you have more than one stop to make, fairly close together? You really need something that'll at least golf-cart.
You'll need heat and A/C, among other things. You can power it all from the rail once you get there, but you can't take the works out of the car.

That, or everything belongs to the People's PRT Collective. Which won't fly with a fair number of the voters you'll need to support it. In the US, anyhow.

Just keeping the discussion going...

cmf-seattle said...

Crazy idea: make the guideway so cheap that it can be run to anyone's driveway. If you need eggs, and there's a seller who's also got a guideway connection, they can be sent to you.

What made PCs and then the Internet popular? Opportunity.

akauppi said...

Vacuum pipes have been suggested for this kind of goods delivery since the 1960's. Never seems to actually happen.

Dan said...

Hi qt.. Glad you dropped in to keep things alive, while I ponder some design issues for my next post. And speaking of issues, here are some that would have to be addressed with privately owned vehicles:
The case of a vehicle that is not properly maintained stalling on the track and stranding the trailing vehicles, the case of a vehicle not communicating properly, creating an unsafe condition, the possibility of the vehicle being modified by the owner in a way that is detrimental or dangerous, (like being hacked to have manual control or carry excessive weight) the possible use for terrorism or other illegal activities, the case of evolving standards and compliance with them.

I still believe that a PRT “pod” would make a bad car, and a reasonable “car” would make for a bad PRT system. Even little compact cars weigh too much by a lot, imho. I know not everyone agrees.

I might mention that a lot of the track design work that I have shown is a “beefier” embodiment; if there can be more supports (from above or below) and it is a straight run, there’s a lot of steel there that can be removed, and I am all for that. The lighter the track the better.

As for “miles being equal,” I’m thinking primarily of travel to parking or major retail centers where the route is fixed. It would show up as another station, and it would be in range or it wouldn’t be an option. Again, I see this as a stopgap measure for where the track hasn’t or can’t be built. Sometimes, after all, there is already pavement right there that is free to use.

I guess I may have soured a bit on the dual mode possibilities, as I have considered the effect of all of the extra weight even something like the EN-V would add, although I guess it would eliminate the possibility of 3 fat guys with baggage and a handicap scooter.

cmf, since you’re in the mood for “crazy” ideas, what about a piggyback rail system for maintenance, evacuation, and even some light freight in the meantime? The second system’s maximum size configuration would be, I guess, for a single human. More generally it would be for sub 100 lb. freight, and the “vehicles” would self-distribute and time themselves to avoid loading the track with excess weight. The secondary track might separately branch off to go into businesses. Shades of Cabintaxi!

qt said...


Well, as long as we're keeping things alive...

The problems you mention all assume the dualmode vehicle would be an "active" participant in the PRT system. But you're talking about a suspended system. Which means the motor, wheels, etc., on the vehicle wouldn't be in play at all. Dead weight is a problem, but stalling, not communicating, etc., wouldn't be.

The tracking and so on, like the motor, would be in the section that's permanently on the track--the "pallet" (as Mr. Anderson would term it). The only part of the "car" that would be relevant would be the interface--the mounting lugs, attachment hardpoints, etc., plus the communication between the "car" and the "pallet". Strictly speaking, the car wouldn't communicate directly with the system at all. And if it wasn't communicating with the pallet properly, it couldn't leave the station.

Doesn't get rid of the whole problem, but I think it would be simpler than what you're thinking.

As to the "bad pod, bad car" aspect, I agree. But sometimes a compromise is worthwhile. As a totally off-the-wall example, the general wisdom is that a motorsailer is a lousy cruising boat--it neither motors as well as a motorboat nor sails as well as a sailboat. However, several respected designers have built boats that MOTORSAIL quite well. They use the disparate modes to complement each other--the sails reduce the size of the fuel tanks needed for long voyages and the size of the engine needed to maneuver in bad weather, while the engine simplifies the sail plan (you don't have to design it to move even if there's barely a breeze) and the hull design (you don't have to build elaborate keels and centerboards--the engine can make up for deficiencies in windward ability).

In other words, if you keep firmly in mind what you're compromising and why, it can be worth it sometimes.

As to weight problem, I agree there, too. But the "three fat guys and a scooter" problem will be with you still, as long as the ADA is a factor. One solution might be to include "overweight" detectors in the pod system. In which case, enforcing weight restrictions on the "cars" would be doable in the same way. Perhaps with surcharges for high but legal weights--the car is two extra people when you pay for the trip, for instance.

Don't know if the compromises would be viable, but I don't see any show-stoppers as such. At least from my non-engineering point of view. And you do talk about keeping options open unless the doability isn't there...

qt said...

Oh, yeah. Just in case I didn't mention it, I'm NOT talking about SUV's or even SMART's. The EN-V (or a cruder but equally small competitor) is about the upper limit I was thinking about, too. For an urban system, we're talking about a rail and a golf cart (in a manner of speaking).

When I think about "real cars" in a dual mode system, I think about INTER-city travel, not IN-city. Taking the AutoTrain to see Grandma on the farm a hundred miles from Memphis, or the like. Not the same thing at all.

Just so we've got the terms straight...

Andrew F said...

Seems to me that a dual-mode system using something with a size on the order of the EN-V may not lead to substantial compromises on the guideway side. Guideway utility increases faster than cost against payload weight up to a certain inflection point which might be around 1000 kg or 1500 kg. I say that the utility goes up because I think the sweet spot for handling freight is in the area of 2000 kg payload. Limiting freight to loads under 500 kg might mean that each load is too small and requires too much handling at either end. A 500 kg payload capacity system would likely still be useful and used, but the economics would probably work better with slightly higher capacity. And freight is a great way to pay for the infrastructure. PRT is like a nuclear plant. It can churn out cheap transportation 24/7, but the demand for transportation of humans has large peaks during the day that drive system sizing, and will be underutilized for much of the day and night. Running freight adds a lot of value without a lot of cost.

Veering back from that tangent, I'll note that the Smart Fortwo has a curb weight of 730 kg. Add people and luggage and you're looking well into excess of 1000 kg.

I have to wonder why people would necessarily have any desire to spend $20,000 - $30,000 on a crappy low-speed, low-range vehicle with no cargo capacity. It would be at least a second if not third vehicle in the family. Is this really a valid paradigm for PRT? Or would it be like Prius, with very low uptake?

Dan said...

You are quite right qt. I was distracted I guess. The bogies should have some autonomy from the cab in this situation. There does need to be a certain amount of control within the cab, but not in the aspects that would cause the problems I outlined. Bogeys need independent control. Thanks for setting the record straight.
The lure of more capability with greater weight capacity is powerful indeed. Many PRT designers have endorsed the kind of weigh limits you suggest, Andrew. I, however, am not one of them.
I think the sweet spot for PRT, as a people moving service, is more like 120 kg, but ADA-type restrictions force the acceptance of much heavier loading. After all, the average automobile occupancy is only 1.4 people per vehicle. The cost of the track that would be adequate for those loads is, by my guessimation, at least twenty times cheaper than for what you suggest. So what would you rather have? 20 km of track or one? (OK, that’s unfair, since I’m not including stations, but still…)
I do not, however, endorse the 120kg weight limit and the dirt cheap track it allows since the big fuel sucking US cities require both higher speeds and ADA compliance. I am forced to accept something many times more costly. There is a cost curve where the difference between 150kg and 450kg is perhaps 6 fold, yet the same 300kg added to a 1700kg system might only add 10%. This is why it is so irresistible. Cmf could probably speak to this better than I, but it seems to me that Raytheon got sucked in to tune of 50 million per mile. (thirty five million over a lighter system) I have never totally agreed with all of Ed Anderson’s design choices, but in regards to the size of the track and the reasoning behind it, I am in 100% agreement. It’s a pity about the freight.
I have seriously considered (within this blog, I believe) that a heavier capacity trunk line capability might be included as a future option and that PRT vehicles should be compatible with it. I just don’t think that kind of track should be making it into most neighborhoods. Just think of the forces that 2000kg applies, say, going around a turn. Or ten of them slamming on the brakes in an emergency. Do we really want to build for that when the average human payload is so much less?
Oh yeah… Good point, qt, about weight limits. I was thinking the same thing and I’ll bet it’s easy to do these days, in terms of sensor hardware. It would really simplify a lot of things, and even enables stuff like variable safe headway maintenance.

qt said...


Dan wouldn't hang a SMART on his rail, I gather. He seems to think the EN-V as about the upper limit. For an in-city system, so do I.

Myself, I'd go for a weight limit, a set of dimensions, and a standard attachment interface, with something like Bluetooth to let you enter a destination. Then let the market figure out what kind of drivetrain, etc., would work best. The SMART is too big. I suspect the EN-V would be too pricey.

qt said...


120 kg? 250 lb? There are days I couldn't even get on it! :-/

More seriously, the "ski lift" approach to PRT does sound kind of nifty. It might even be workable in a campus situation or the like--where handicap-friendly alternatives are part of the overall mix, rather than required of every single transit choice.

(Hey, nifty. And I haven't heard anybody seriously discuss taking advantage of that. Mini-PRT for shopping malls, college campuses, airports, etc.? Everybody wants to build big there, too...)

(See what happens when you run off at the, um typing fingers?)

But as you said, ADA will force real weights on you anyway, in a city-wide transit system. And if you have to build it to haul the fat guy and the scooter, you might as well add the last-mile solution as an extra selling point.

And it is one, I think. If I'm just going to visit someone, I might not bother--I actually enjoy walking. Or I can carry one of those little electric kick-scooters (I've got one I carry in my semi in warm weather, just in case--not even electric...). If I'm going a little further, or carrying a little something, my folding bike with a handlebar basket is good for a fair bit.

But even I want a way to get around the neighborhood in comfort in hot or cold weather. Or if I have more than a couple of small shopping bags. And if I could get something like a golf cart as a second car--for a reasonable price--AND use it to run errands on the other side of Atlanta as a bonus...

If you've got to build the rail that big anyway, it's at least worth thinking about.

Andrew F said...

If you have to carry four passengers at up to 150 kgs plus some belongings, you're not far from a 750 kg payload anyway. That's about a pallet of reasonably light goods.

Limiting the system to 120 kg payloads would make it useless for freight, and of limited use for persons.

There's lots of interesting applications out there. One of the PRT proponents suggests moving heat on such a system. You can take waste heat from industrial processes and power plants in the form of hot water and deliver it to buildings throughout a city without an elaborate network of insulated pipes and pumps. I'm sure there's other ideas that no one will conceive until the infrastructure is in place. Light weight is nice for cost, but ultra-light weight will mean ultra-limited potential applications.

Andrew F said...

That said, of course, I could see potential for light-vehicle-only loops off of the main network that will run down suburban streets, etc. But, I would expect the main trunk lines along thoroughfares to be capable of handling heavier loads. Maybe we're not disagreeing after all, Dan!

I can also envision a much-scaled up system capable of carrying cargo containers and running along rail ROWs and highway medians, but capable of moving freight from the west coast to the great lakes in maybe 36 hours, or fresh fruit and vegetables from California and Florida. There's a lot of room for value creation there. Consider something similar in Europe, which has a woeful cargo rail network and higher fuel prices or China and India, where they simply don't have the room for all those highways.

Dan said...

I’m going to move to the next thread as far as general configuration matters are concerned. I would, though, like to address Andrew’s comments about freight here. (not that talk about freight isn’t welcome in the next post, just that we are already on the subject here.

I, personally, do not see any real benefit from designing the system for palletized cargo. I think that the real problem is that the current road system is designed for trucks, yet is congested by cars. Most road traffic has a ridiculously small payload (the driver) for the size of the container (the car) and the massive infrastructure that it is rolling over. The real problem is that cargo can’t get through the auto traffic, not that a road is such a bad way to move heavy loads. It seems to me that the heavier something is, the stronger the case for leaving it at ground level. Energy wasters like traffic lights or stop signs can be largely dealt with through automated navigation and computerized right-of-way management. Also often pallets are often holding a large number of items that could be packed in smaller groups. Some of the reasoning behind the quantities of items shipped has to do with the fact that there are human drivers to pay, and traffic to contend with. Perhaps PRT would encourage mini “just in time” shipments that would reduce the need for giant warehouse stores laden with excess inventory.

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