This the first of two guest posts is from commenter “Icebird” looking at PRT.  This post is solely the opinions of “Icebird” and not of the Auckland Transport Blog. 

The (eventual) future of public transport?

Nick R has made several persuasive posts on this blog for consideration of “automated rapid transit” or “light metro” as a solution to some of Auckland’s transit issues.

If you’re familiar with some of my comments on this blog and on the CBT forums, you might remember me for lobbying for a different horse in the “innovative transport solutions” derby:

“personal rapid transit” or “PRT” for short.

I wanted to take the opportunity of a guest post to more fully explain just why I’m still enthusiastic about PRT even in the face of widespread skepticism from many, and even outright hostility from some. Nick’s ART system certainly improves on traditional rail systems in many ways, and it’s a very attractive technology. But at the heart of it, ART is still basically a rail system, with both the pros and cons of any rail technology. But if PRT can prove itself in high-capacity operations, I think it could be a game changer, fundamentally altering the way we plan public transport systems and even how we design our cities.

In this post, I’m going tell just what PRT is (for those of you not familiar with the concept), try to explain why I’m so excited about the technology even in its current, mostly unproven form, give you a bit of a rundown on the history of PRT development (trying to answer the question “if its so great, why hasn’t anyone built a PRT system yet?”), outline some of the challenges that still have to be overcome, give my first-hand experiences of riding the “Heathrow Pod” PRT system, and float some ideas about where a potential Auckland PRT system could be built.

Designing the perfect public transport system

Almost every current form of public transport represents a compromise of some sort. There’s probably a bus stop within walking distance of you right now. But the bus that stops there might not take you directly to where you want to go, and its still subject to the vagaries of traffic, so its rarely going to be faster than driving a car without additional assistance.

Trains? Trains are much faster. They don’t have to share the rails with all those cars for one, and there are fewer stations, much further apart. The downside is that there probably *isn’t* a train station within walking distance of where you are right now. So you might have to drive or take a bus to get to the train.

Now imagine for a second that you were designing the perfect public transport system. What would that look like from the passenger point of view?

For a start, there would be spots to board a vehicle all over the place – think bus stop level coverage, rather than train station level of coverage.

Waiting for vehicles to show up at the stop? Forget about it! I want the vehicles to be waiting for me!

And when I board the vehicle, I want it to take me non-stop to my destination. No stops to pick up or drop off other passengers. No changing vehicles. No stop lights. And I want to be able to go from any stop on the network to any other stop on the network.

Oh yeah, and I also want the system to run 24 hours a day, 7 days a week.

Sounds like a pretty impossible combination right? Using public transit would be more like hailing a cab than getting on a bus.

Here’s the thing: PRT could actually potentially deliver that level of passenger service. I’d be a fan of the concept for that alone. If it could deliver that passenger experience – how many car drivers might decide to use the system, even if they weren’t compelled to by extortionate parking fees?

So what is PRT?

Start with a small passenger vehicle that can carry 3-6 people. Give it computer guidance so you don’t need a driver. Put the vehicles on their own track – at ground level if you have the land available, on an elevated guideway if you don’t. Put the steering gear in the vehicle so you don’t have to put switches in the track.

Then take the stations off-line from the main track (like a siding on a railway line). Vehicles stopping at stations don’t impede any of the vehicles behind. Your pod can bypass all the intermediate stations between your origin and destination.

Empty vehicles are automatically re-routed to restock empty stations. At off-peak times, a vehicle should always be waiting for you. At peak times, you should only have to wait a few minutes at most. Can you imagine a transit system that provides a higher level of service at 3 AM on a Tuesday morning than at 5 PM on a Wednesday afternoon?

Because the tracks don’t have complicated switching mechanisms, you’ve got much more flexibility in how you lay out your network. Forget long, thin corridors like traditional rail, and imagine instead a connected series of one-way loops, with new tracks constantly forking from, or merging with, the track you’re currently on.

Within those basic parameters, there are various ways of executing the design. The Ultra system uses vehicles with fast-recharging batteries and a sophisticated laser guidance system. The pods recharge while docked, and the guideway infrastructure is largely passive, keeping the construction costs low. Other systems have proposed using linear induction motors, or more fancifully, “mag lev” propulsion.

Here’s the amazing thing about PRT for transport planners: it should be cheap. Elevated guideways sound expensive, but they only have to support small light pods, rather than large, heavy train carriages. So the guideways can be quite small with, relatively speaking, an unobtrusive footprint. A light narrow guideway is easier to integrate into the existing urban environment (by running it above sidewalks or carparks). It can accommodate tight turns and steep climbs. You could attach guideways to existing bridges (I’m looking at you, Auckland Harbour Bridge!).

I attended an Engineers for Social Responsibility evening where the New Zealand holder of the Ultra licence talked about the technology. The cost number he quoted for the system? $13 million per kilometre – total system cost, including guideway, vehicles and supporting infrastructure. That’s pretty competitive with any competing rapid transit technology. As Nick as noted in his Light Metro posts, any driverless system leads to massive saving in ongoing operating costs.

Furthermore building a PRT system doesn’t require an all-or-nothing commitment. You can start small, then expand the system. The nature of the system means that vehicles have the freedom to pursue alternative paths between to their destination. That means that part of the system can be shut down without necessarily affecting the rest of the network. Thus you can continuously expand the network in an incremental fashion, rather than the current model where the rapid transit network tends to expand in large, very expensive chunks, with little activity in between.

Go on, what’s the downside?

This sounds a bit too good to be true, so your skepticism levels might be on high alert. The debate between those who passionately believe in the technology, and those who believe it cannot and will not work is vigorous.

The first major problem of PRT is that its largely unproven. The first “modern” systems have only just rolled out, and only in low-capacity operations that don’t really test how the technology will perform in a busy urban environment. Many of the benefits of PRT will only be realised if it can be succeed in high-capacity operations.

The conveniently brings us to another issue frequently raised in opposition to PRT: “It doesn’t have enough capacity”.

Now a high-frequency rail system will have a higher absolute capacity than PRT. I’ll happily concede that point. But PRT might very well have enough capacity.

The Ultra system is currently licensed to travel at 40 km/hr with 3 seconds gaps between vehicle’s by Her Majesty’s Rail Inspectorate in the UK. This is very conservative licensing. On a motorway, the recommended gap between vehicles is 2 seconds travelling at 100 km/hr. So if the gap in the Ultra system was lowered to 2 seconds, the guideway would have the same capacity as a lane of motorway traffic. (Ultra is aiming to increase the speed allowed by the license to 80 km/hr).

The real benefits of PRT start to kick in however when you lower the gaps between vehicles even further. A commonly cited “target” by PRT developers is half second intervals between pods. Even factoring in capacity lost due to empty vehicles being redistributed throughout the network, PRT’s capacity begins to match about three lanes of motorway traffic – at a fraction of the land allocation.

High-capacity PRT and high-frequency rail aren’t necessarily in competition with each other. The existence of motorways doesn’t negate the need for a local road network. There are opportunities for PRT to act as a feeder to the rail network, bringing rapid transit closer to a much large section of the population than now. Think of PRT as a bus replacement technology, rather than a replacement for the rail network, at least to start with.

The other major obstacle I see to PRT’s adoption is visual intrusion or the “NIMBY” factor. I don’t think there’s any getting around the factor that an elevated system, even with all the mitigation in the world, will always cause some visual intrusion. If you presented the plans to the good citizens of Auckland today, I’m sure most would say “not on my street”. If you built a system somewhere non-controversial (like Wynyard Quarter perhaps) and they could try it, and ride it, and it lived up completely to all the expectations I’ve laid upon it… I think they would still say “not on my street” but might demand that it be built one street over so they had a station within walking distance.

In the next post Icebird talks about the history of PRT, his personal experience and potential applications in Auckland.

Share this


  1. At a stretch I can see how this system might work in certain areas. Perhaps as a connection between Airport terminals and carparks, or in similar cases to the Roosevelt Island tramway in New York City – not much demand and very challenging terrain to provide any other technology across.

    But really, at high levels of demand or across large parts of the city the idea just seems to be impossibly nonsensical.
    – Elevated guideways down all our arterials – geez think of the horrible visual effects.
    – Needing thousands upon thousands of pods everywhere: geez think of the cost (the genuis of the private transportation system is that cost gets loaded onto us suckers who own cars).
    – In areas of high demand: well I don’t really fancy the idea of having these whizzing much closer than 2 seconds after one another – which puts a significant capacity constraint on the system.

    So yeah, OK in certain areas but generally PRT advocates suggest that they’re the solution for everything and can replace all types of public transport. (My word if I ever see that Skycabs guy again I’m going to go insane). That just discredits the whole idea.

      1. Yeah the idea is old (just like flying cars), However the restricting factor has always been getting it to work computationally. Available computing power doubles every few years making the software challenge that much easier.

        Take a look at the Darpa grand challenges… We really aren’t that far away. When computers collision rates drop below that of humans it makes logical sense to swap over.

        1. “When computers collision rates drop below that of humans it makes logical sense to swap over”

          I suspect that has already happened based on what I have read. But the battles of cost and legal restrictions will be higher.

          I agree driverless cars will effectively give us a PRT network. My thoughts are:

          Taxis will become very cheap. Therefore car ownership will decline. This will lead to a transport system where all modes are effectively public, and services will vary across a continuum from a private taxi to full scale rapid transit, with demand-reponsive shuttle services and conventional bus services in between.

          Other effects – parking will become much less of an issue, no need to store cars where you work (or live) if you dont own them.

  2. I’d like to thank Matt for lending me a soap box here. I’ll be keeping an eye on the comments thread to answer any questions I can.

  3. I think that the only real practical applications would be as a feeder type service to a higher capacity mode e.g. feeding people to and from rail stations or around spread out commercial areas like Albany. The big killer for it though would be if it needed to be on its own guideway, the visual impact would be far to much for most people.

  4. “High-capacity PRT and high-frequency rail aren’t necessarily in competition with each other.”

    I would say PRT would only be of use in conjunction with high frequency rail, bus or ferry. PRT might be a good solution to the last mile problem, a sort of circulator in CBDs or other areas. Albany perhaps?

    But three just seems to be no way it can be a single panacea, not that anything really could be. It’s really the same as a driverless car system, if we build one for everyone to use why would it be fundamentally different from the way our roads are today?

    It was mentioned above that PRT could have the capacity of a motorway lane if the technology continues to develop… well that kinda proves that it’s no good for the backbone of a public transport system. That means we’d need a six lane PRT freeway just to carry the same amount of people as the northern busway does today, or about ten or twelve lanes to match it’s maximal capacity. I don’t think we can attach ten PRT guideway lanes to the harbour bridge.

  5. PRT strikes me as perfectly combining the worst aspects of car system and the worst aspects of rail systems without the advantages of either. Just doesn’t make sense anywhere outside of Disneyland.

    1. …plus the need for an entirely new network of infrastructure which will need to correlate to a large part of the road network in order to obtain catchment, and positioned within highly constrained local road space. Few will give air rights over private property for this type of installation. The real costs of negotiating space in the public road reserve, and obtaining consents, will make a mockery of the quoted costs of a system. I’d love to see a concept drawing and modelling of passenger flows/waiting patterns for one of these installations serving Symonds Street for example. I suspect the scale of interchanges and offline loading stops to enable the main network to flow freely would be horrific. Forget a city with trees along the streets.

      It’s an interested concept for settlement of Mars, but I think the argument for it falls apart when you ask how it marries up to present reality in most urban areas. It’s effectively loading more demand onto the local street network while looking decidedly hopeful rather than proven in terms of any improvements in capacity or speed. I suspect Nil advantage, huge cost.

      1. I went to Engineers for Social Responsbility meeting where the NZ right-holder for Ultra was giving a presentation. He said he had received quite a positive response from commercial property owners – by integrating stations into their buildings at first floor heights, they could then charge ground floor rents to other oocupants at that level.

        How you choose to integrate the system with the existing roadworks would largely depend on the road in question. Jervois Road and Ponsonby Road have large painted medians for instance – you could run the main guideway down the middle of the road, with the guideway branching off to the side of the road for stations. On other streets, you might run the guideway over top of parking spaces for instance.

        In most intances, you can get away with running a guideway in only in one direction along a street (think of network design in terms of interconnected loops rather than long thin lines), so complex interchanges don’t really exist – guideways are either merging together, or diverging apart. I’m not really sure how you can say its loading *more* demand on to the local road network when its more about creating a completely parallel infrastructure to *reduce* demand on the local road network.

  6. the real issue with any elevated system is public acceptance and thus getting consents, it’s hard enough to get bus stops and shelters in, but “an elevated PRT station outside my house where Joe Public could look straight into my teenage daughter’s bedroom? Not a snowball’s chance!”

  7. I don’t see what the benefits are. Sure you’ve listed the benefits of PRT over traditional rail and bus, but they’re the same benefits that cars already have over rail and bus. So we spend $13million per kilometer AND wait for a whole lot of improvements in the current technology AND build what are essentially ugly flyovers all over town and we end up with a mode of transport that is almost as good as a car. You save the cost of owning and maintaining your own car, but on the other hand you’d presumably have to pay a fare. And you’d still need to walk to a stop, whereas most of us have a car sitting on our drive or close by.

    I think maybe you’ve just assumed the benefits are obvious and so haven’t bothered to list them. They’re not… to me at least.

  8. Years ago, I was talking with a Wellington City Councillor about extending the railway line south of the station, and asked if it could be done using some sort of elevated railway. I was told that that would be absolutely impractical; any extension would have to be underground or at-grade. This technology is an interesting one, but its use of flyovers and elevated track is a massive disincentive to its wider use.

  9. It’s just about trying to reinvent the car, but in a much less practical, and much more expensive way.

    And just think of the etching, graffiti, rubbish and urine that you’ll find in them! Or will there be a few hundred people cleaning them all day and night?

  10. Heh, comments thus far going pretty much as I expected. I can fully understand skepticism that PRT *will* work – but isn’t it the kind of public transport system you would *want* to work?

    Anyway, to address a few of the specific issues raised so far:

    @Nick R : I think you misread what I wrote about capacity. In a “high capacity” operation (vehicles operating with half second headways), PRT’s capacity would be equivalent to the *three* motorway lanes. If a particular route demanded more capacity than that, its probably a candidate for a busway or rail system. As I eluded to in my post, PRT lends itself more to dispersing demand across multiple routes than rail systems.

    @Nick @Geoff @Obi : “It’s duplicating the car network!”. To a certain extent true – but better. I’ll give you one good reason why PRT would be better than a car trip : non-stop journeys. You don’t get stuck in heavy traffic, you don’t have to stop at red lights, and you don’t have to find a park when you reach your destination. Plus its cheaper (since you’re essentially just renting your vehicle for the duration of your journey). I think this blog have covered both the obvious and hidden costs of motoring in great detail.

    @almost everyone : Visual intrusion. I’m not going to deny that visual intrusion is going to be a major sticking point for a lot of people. Is it an insurmountable obstacle? I don’t think so. When it comes to consideration of any transport infrastructure, I think people weigh up how disruptive it will be to them compared with the potential benefits it will bring. The Auckland motorway network is about as intrusive as it comes with massive viaducts, numerous flyovers, and acres of concrete – yet there doesn’t seem to be an active “tear up the motorways!” lobby. Close neighbours of the motorway may not like it, but they accept it as a necessary evil. The lightweight infrastructure required to carry small pods would be less disruptive than virtually any other form of rapid transit apart from perhaps bus lanes.

    1. Non-stop journeys? I think not. As soon as you have any sort of junction with one or more of the legs running minimum headways there will be a need to stop one of the routes until there is a suitable gap in the traffic. These claims of vehicles waiting for users at stations and no stops in the journey assume a surfeit of capacity over demand.

  11. Nice article. I am cautiously supportive of this idea. It is no silver bullet, but has great potential. A large cost of PT is labour and this system would reduce it. An electric based system would be far more sustainable than oil based transport. I see it supporting rail but if the PRT line gets overloaded, simply increase the prices at the choke points and the demand will sort itself out. Unfortunately, it will happen far later than we could have it because people generally lack vision to see the potential. The canal owners used to laugh at early rail. The carriage builders used to laugh at automobiles. One day we won’t be able to afford the petrol to drive our cars. Driverless cars are a nightmare and technology is in its infancy, it will be decades before sensors are capable of driving safely in an environment where pedestrians jump out in front of vehicles all the time. The human eye is a marvel that engineering science has yet to replicate.

    1. “it will be decades before sensors are capable of driving safely in an environment where pedestrians jump out in front of vehicles all the time. The human eye is a marvel that engineering science has yet to replicate.”

      You might be surprised at how far LIDAR technology has come recently. I have seen some demonstrations with very much non-state-of-the-art equipment, and it is very impressive.

      1. Sensors are great at detecting something getting in your path. That’s why automated cars in testing will slam on the brakes when a plastic bag flies in front of them! Great at detecting potholes as well….unless they are filled with water, in which case in you go. The best way for a car to be driven is to put a person behind the wheel.

  12. I think the visual impact would be the greatest barrier to this system. For the kind of bus stop coverage you’re talking about, there would be literally thousands of pylons across the city. Yes the motorways are ugly, but aesthetically they only impact the people living closest to them. These pylons would be everywhere and affect everyone.

    Maintaining thousands of these pods would also be a pain in the arse.

    Sorry for the negativity, but I would rather see an extensive light-rail network or under-ground metro for the inner-suburbs, complimented by high-speed links to the outer-suburbs.

  13. Hmm. I would be supportive of us building some of those nice swooping elevated roadways and running bikeshare on them – of course, purely as an interim step, y’know? #cycletroll

  14. I think its hard to say what system we ‘want’ to see. Some of us are rail or bus gunzels, and want to see rail or bus respectively regardless.

    Transport should always be seen in terms of efficiency, economic, social and environmentally speaking.

    Powered transport only exists because it produces productivity improvements over walking, and cities only exist because of agglomoration benefits.

    The comment above was right – motoring tricks its users into purchasing the vehicle, and by making the vehicle sexy people take ‘ownership’ of the vehicle where in fact they are quite expensive pieces of equipment and depreciate very quickly. Hence quite irrational to actually own one, EXCEPT where you get some hobby value out of it. But to own it simply to get around when there are good trains or buses, is irrational.

    Except it isn’t irrational BECAUSE there aren’t good trains or buses in NZ or Aust, by comparison with other places.

    Cities are cities. Decisions on how cities are built are always political (even laissez-faire requires a political decision to ‘laisser’). So the shape of your city is the outcome of decades of political decisions, nothing natural about it. Other cities chose differently, they don’t need PRT because they are immediately walkable with fixed rail and good bus transit backing up the unwalkable journeys, and motor vehicles in a residual role.

    In fact, Auckland having isthmuses and peninsulas should have made it easier for buses and trains (and provide ferries as a viable alternative) but the choice was made to favour motoring, with its vehicles ‘offloaded’ onto the user.

    Personal Rapid Transit solves a problem that has yet to be invented.

    If we’re talking futurism, I’d rather have the flying car thanks. Plenty of space in the skies!

    1. PRT is here already. Fortunately flying cars are not. Adds a whole new dimension to drunk driving!

      What is easier? Changing the fact we all live far away from where we work/shop/play or changing how we get to and from these locations? Obviously the former is more preferable, but the latter is more likely. Buses and trains make no sense off peak. Private vehicles rule the off peak due to convenience in a way bus/rail never will. Having buses and trains alone in a car dependent city is useless because most people will still need to own/use cars. In a well designed PT network, PRT will increase rail and bus usage and will give people less reason to own cars.

      1. Flying cares are here already, but like PRT they are very small niche applications still in a development phase. The fact a few models of flying car exist doesn’t prove they could ever be adopted on a citywide scale. Likewise pseudo-PRT applications as a carpark circulator or a university shuttle don’t prove that PRT could ever work on a citywide scale.

        Sorry if I’m being rude Ari but comments like “Buses and trains make no sense off peak. Private vehicles rule the off peak due to convenience in a way bus/rail never will” sounds like you have spent your whole life in some outer NZ suburb. Buses and trains make perfect sense off peak, even more sense than car ownership, parking provision and all that goes with it. I’ve lived in cities overseas where owning a car is a liability. In Buenos Aires and inner Melbourne a private vehicle is expensive and the slowest form of transport you could pick, even in the off peak. To much traffic, too many traffic lights, too much time wasted looking for car parks or circulation in parking buildings… it’s much faster and more convenient to simply take the bus/tram/train which run very frequently, connect across a wide network, and consequently stay full all day and don’t cost much as a result.

        The fact that Auckland’s conventional public transport system is one of the most inefficient and ineffective in the world doesn’t mean we need a fandangled automated pod network to increase rail and bus usage. All we need to do is redesign the system to something like the rest of the world uses.

        1. Nick, you aren’t being rude, this is just a discussion between people who want to improve things. We both agree that PT in Auckland is bad and that it needs to change. Bare in mind that I am coming from a resource consumption perspective rather than cars vs bus vs rail vs something else.

          Yes, I am aware of prototype “flying cars” but they are not practical in any way, nor feasible on a large scale. PRT at least has significant potential as a great option in a overal transport mix that can scale at lower cost than rail.

          Regarding my off peak comment, I am talking in the context of Auckland of which many people live in the outer suburbs. I know things may be different in other cities, but in car centric Auckland you need a car or you choose to miss out on various social activities.This leads onto another big topic of why people don’t live near where they work/socialise but that is a whole other topic.

          I often go out to visit friends at night who live on the other side of town. It is no way financially viable to run a bus/train at midnight for even a few people. Thus, cars rule the off peak. Even at peak times it is quicker and cheaper for me to take a car. Sure, if they increased car costs it may make PT more attractive, but generally in Auckland during the off peak, taking a car is quicker than bus or rail. Until that changes, Auckland will remain car centric.

          I see PRT as a way to get people out of using cars altogether while remaining financially viable in a way that buses or rail may not and consume far less resources than a car dominated transport system.

        2. My point was that you are looking at the status quo and effectively saying that our worlds-worst public transport can only ever be the way it is now, awkward, expensive and disfunctional. Auckland isn’t car centric by the will of God, it’s car centric because we’ve spent decades dismantling our public transport system and only spending money on roads and car infrastructure.

          We don’t need a brand new automated pod network to make public transport work, it would be far cheaper and easier to simply make public transport work. Buses and rail can indeed get people out of cars and remain financially viable. The system needs a big overhaul for that to occur, but that basically just a matter of planning. We have almost all the vehicles and infrastructure we need for world class public transport already.

          If building an entirely new PRT system right across the outer suburbs is the answer, we really need to revisit what the question is!

    2. Car ownership is only irrational if you want to live a life where you only ever go where buses and trains are. For the 99% of us who value freedom of movement, the car is by far the best way to get about.

  15. motorways are not a valid comparison, by their nature, they’re not common, but to be effective, PRT would need to be pretty much within walking distance of many homes, at least as much coverage as the bus network, apples and elephants

    the other issue is occupancy, with dispersed travel patterns, it’s unlikely that the vehicle would be full except at peak times, therefore there has to be quite a bit of redundancy built into the system to accomodate this diversity, plus all the energy needed to relocate empty vehicles to stations as you suggested

    where I can see an application is in major airports moving people between check-ins and gates, but I just can’t see it as providing a viable urban transport network

    1. I’m not sure what you’re getting at with your first sentence Steve. You’re right that you would probably build it densities closer to the local roading network than a motorway network, but the potential carrying capacity and smooth-no-stopping-operation are closer to the motoway travelling experience. (And no, I’m not suggesting that the entire Auckland region will be blanketed in guideways overnight).

      Maximising the occupancy of each pod isn’t the point of the system. Like a taxi, the point of the pod is that will go non-stop to where *you* want to go. You can charge trips “by the pod” rather than “by the passnger” (again just like a taxi) as an economic incentive to share a vehicle if you happen to be in a group going to the same place. In terms of energy use, I’m not sure you’re wasting any more energy relocating vehicles than in traditional transit systems, where for every full train or bus heading with the peak hour traffic, there would be a significantly more empty one heading against the peak traffic flows. And the overall energy use of the Ultra system is pretty low.

      Sure there would be a bit of redundancy in the system, but I think thats true of almost any transit system, where the resources required to move people at peak periods are far greater than in off-peak times. But PRT would have a lot of flexibility to adjust fluctuating demand patterns by moving vehicles to where they’re needed, and having lots of vehicles to cope with peak demand means at off-peak times there would always be a vehicle ready and waiting at your nearest station.

  16. When I read through the Ultra website my engineer’s BS detector is triggered:
    Claims of very low energy use per passenger-km with no information as to assumptions of occupancy, ac and/or heating provison, starts and stops, whether electricity generation efficiency is factored in etc.
    Failure to point out that by limiting maximum speed of 40 km/h one invariably improves on specific energy consumption.
    Claims that the vehicles are well-proven and reliable when operating systems are few and very limited in size
    Claims that “Analysis shows that most forms of transport, whether they be public or private, have similar levels of energy use and emissions output” (Clearly nonsensical).

    Let’s look at the published data for these vehicles:
    180 Ah of lead-acid battery at 48V. That’s NOT a fast charge battery nor is it a battery capable of heavy cycling. It’s an 8.6 kWh battery to power a 7kW motor plus whatever other ancillaries the vehicle has. In summer add 1 kw of AC load and in winter add 1 kW of heating. Taking the claim of an average 2 kW demand for traction purposes (seems low but we’ll play along). Add the AC load for a total of 3 kW (and that’s ignoring lighting, cameras, LCD, comms etc). Limit the battery to a 50% discharge so that it will last more than a couple of weeks and we get a little under 1.5 hours of use from a full battery. Now to charge these batteries without damaging them we are looking at a minimum of around 6 hours so for every vehicle in use 4 are being charged. Might be workaable if the peak does not exceed 1.5 hours but add in 2 second headways and the question becomes where are all these vehicles going to be charged? Some sort of large parking lot at each station?

    Mention has been made of 80 km/h operation. The current spec vehicle is not capable of it so is this vapourware? Claims of superior enegy efficiency go out the door when these sorts of speeds are being considered. How can this vehicle achieve a claimed three times the energy efficiency of a battery electric vehicle when it is also a battery-electric vehicle and a crude one at that?

    Sceptical? Absolutely. I have seen better piches from second-hand car salesmen.

    1. I would be skeptical of anything not proven, and they still have to prove themselves. I’m suprised they are using lead acid, but I suppose it was based on cost and the fact they are running at such low speeds there would be slower drain on the batteries. Regarding charging, I presume a system with higher demand and further range would require lithium batteries and would have vehicles that use inductive power charging placed into the main guideways so that the vehicle charges while moving or sitting at the station (just like electric vehicle robots in many large factories). In such a system the batteries are only as backups. I presume it would just be the motor that would need changing to increase speed as other electric vehicles go a tad faster than 40kmph.

      1. Inductive power charging? Sure, you could do it but you can forget $13M per km for the guideway/track.

        At 80 km/h the motor power required just to overcome drag based on 25C ambient temperature and still air (ie no wind) is about 7 kW (using the published dimensions and an estimate of 0.29 for the Cd). Add in rolling resistance, the need to overcome headwinds and perhaps a soft tyre plus the need to accelerate (at say 1 m/s²) and climb and a 35 kW motor is more realistic.

        Consider, also, that at design speeds of 80 km/h there will have to be acceleration and deceleration lanes parallel to the main guideway. With a 1 m/s² acceleration rate (and assuming that the motor power is sufficient to achieve this) these lanes will need to be 220 m long each side of a station. Add in say 30 m for the station itself and we are close to 500 m of double-width guideway for the station.

        1. I’ve enjoyed reading analysis based on engineering and physics. It brings some rigour to the discussion. Thanks! Can I ask if you get a feeling that the figures are wrong the moment you see them, or do you have to do the calculations first?

        2. The impression is that the published figures are generally not wrong (with an egregious exception or 2) but are carefully selected to illustrate absolute best-case scenarios and important assumptions/conditions pertaining to these assumptions are not stated. For example the claim that these “pods” are 3 times more energy efficient than an electric car requires, I suspect, that the pod travels at no more than 40 km/h whereas the electric car travels at 100 km/h and stops and starts an unspecified number of times but since the conditions are not stated that is just a guess. I am suspicious as to the reasons why relevant facts are not given. The claim that these pods are so much more energy efficient than *any* other form of transport instantly sets alarm bells ringing.

        3. You might have doubts about how the system will scale to higher speeds, but Ultra ought to have a pretty good idea of the power usage of the system as it exists at the moment – the Heathrow system spent almost two years in testing, and they were running the test track in Cardiff for several years before that. My understanding is that vehicles charge up at the stations, so the batteries are essentially getting recharged any time the vehicle isn’t actually moving.

          The Taxi2000 aka SkyWeb Express system proposed using Linear Induction Motor drive technology (as used by Vancouver’s SkyTrain) which always seemed a more elegant solution to me than batteries, but Ultra got funding and Taxi2000 didn’t, so here we are with battery-driven vehicles. But batteries are from the only way to build a PRT system.

        4. Recharging batteries is a requirement of the Heathrow system. While recharging is taking place the vehicle is out of service so a key parameter is the utilisation factor – for every hour of use how many hours (or part thereof) is the vehicle unavailable because it is being recharged? Immobilised lead-acid batteries are not known for tolerating fast charging.

          With such short end-to-end distance determining whether a vehicle has sufficient charge to undertake a given journey is relatively simple. With a bigger network and consequent variation in possible journey distance it is not trivial.

  17. my point, icebird, is that there really aren’t a lot of motorways (five, southern, northern, northwestern, southwestern and upper harbour) but to be of any use at all, you would need for a PRT system to have a coverage at LEAST as good if not better than the bus network, therefore it’s not a valid comparison

    and there’s a chicken and egg issue with that coverage, if you don’t have the coverage, it’s not a useable system and if you don’t have a useable system, you won’t build the case for coverage

    with the current global financial issues and the money invested and being invested in conventional PT, it’s just not a goer

Leave a Reply

Your email address will not be published. Required fields are marked *