Sunday, July 4, 2010

93> In Search of PRT’s “Killer App”

I want to dust-off a topic I have posted on before, and add some new thoughts I have had on the matter. The subject, or perhaps the question, regards what kind of routing layout PRT is best suited for, or should start with. Unfortunately I need to get down to some greasy details to make my point.

First I want to point out something about PRT control. In the very early days of PRT, back in the days of the Aerospace Corporation’s involvement, sensor, computer and communication technologies were in their infancy. The logical approach to vehicle control was to have a big computer manage all of the cars like one big machine. That way not much was required in the way of sensors or computing power on board. (Now, of course, we have more computing power in our cell phones than their whole system had.) Merges were conceived in terms of vacant or occupied spaces that were all moving at the same speed, something that can clearly be seen in the video. This required a uniform “line speed.” I am not sure about Vectus, (seems like someone told me it has dynamic speed control) but I believe everyone else pretty much assumes this sort of set speed. (If my information is dated, please correct me!) The going wisdom seems to be that to be financially viable, the track needs to be packed at all times, and so the system must be confined specific, highly urbanized areas. Therefore the routing involves close distances and so the system doesn’t need to go fast.

Then there is the matter of headway limitations. There is a notion out there that vehicles can only go so fast, because the headway requirements increase as the speed increases. Therefore, more cars can pass a point traveling slowly and close together than by going fast and being more spread out. There is a formula that “proves” this. Unfortunately this has led some to conclude that PRT, as a rule, can only go so fast. I have heard specific speeds mentioned.

I believe the arguments listed above are wrong-headed. First, about the packed track/financial viability thing…Perhaps the reason the track needs to be packed is because it is downtown, moving slow, has many stations, only short trips, etc. This all jacks up cost or constrains revenue. Amortizing this cost requires either high fares or a packed track. The per mile/kilometer cost estimates for PRT generally include several elevated stations, assume many long spans across streets, high construction costs because of traffic, buried utilities, etc. Has anyone, ever, given a quote to go across an empty field? Of course not. PRT is too slow to be useful for long haul, and it is too expensive to go anywhere where the track won’t be filled. See where I’m going with this? It’s a circular argument. Maybe it’s expensive because it is downtown and is downtown because it is expensive.

Let’s go back to, before moving on, to that argument about top speed and headway, since nobody is going to trade a 45-minute car ride for a 65 minute PRT ride. It, too, is a false choice. This is because the numbers going into the formula can be changed by simply designing the vehicle differently, and then the answer changes as well. I looked at the formula and found that the variables that must be entered refer to common sense considerations like braking efficiency, response time, and crashworthiness. Therefore any suggested optimal speed or headway distance is the result of plugging in numbers for a particular system’s capabilities. Nobody, (including me, so far) has plugged in the numbers for a system like I have proposed, but I guarantee that the safe headway would be way, way less than for a system where the first part of the vehicle to make contact in a collision is the passenger compartment itself, which is the case all of the systems currently on the market, yet need not be. They don’t need crashworthiness because they don’t go fast, because of, well… more circular arguments.

As far as the controls go, the technology for dynamic speed control is really not an issue anymore. Thousands of calculations can be done in thousandths of a second and transmitted and received with similar speed, although some intrepid programmers need to step forward and write an open-source version of the control software. An example of a demonstrated system (That even works with truly antique computers and sensors) is the PATH program. Insofar as at least some of it was funded by taxpayer money, I sort of hoped that they would at least respond to my requests for the code they used, but, alas, I’m just a lowly blogger…Anyway, with variable speed, another of the factors holding back PRT from being a commuting tool will have fallen.

One note, however… There is the matter of controlling vehicles that run on simple pavement, like ULTra and 2getthere. There is definitely a slippery pavement issue when it comes to going fast for these guys. None of my arguments apply to them. They really do need to keep to routes appropriate to more limited speeds, at least for the time being.

There is the matter of motion sickness, but again, with dynamic speed control, cornering speed would be based on factors including what is comfortable. The individual could (theoretically) even specify the kind of ride they prefer. So the last of the arguments against commuter PRT has been answered. Well, sort of… There is the matter of where to go on the suburban end.

Another thing that has changed since PRT’s inception is the proliferation of “Park & Ride” systems. These are essentially parking lot/bus stops in the suburbs, which are sometimes used in combination with HOV (High Occupancy Vehicle) lanes. The commuter can take the bus or carpool to bypass the clogged freeways. These lots are ready-made outlying destinations for PRT. But why not just take the bus? Because if there is no HOV lane, the bus gets just as stuck in traffic as the rest of the commuters. If there IS an HOV lane, it too, will become clogged over time, when (in some cases) it will magically morph into a toll lane. (Funny how that happens!) Also, upon exiting the HOV lane, the bus cannot take passengers to all of their respective destinations efficiently. And HOV lanes are usually one-way. (reversible) The buses face ordinary traffic on the return trip. Anyway, these Park and Ride lots are generally on inexpensive land that is very close to the freeway and would be cheap to connect to. True, the passengers would have had to drive to these lots, but don’t forget, the downtown traffic comes from somewhere. Typically, the first part of a morning commute goes pretty fast. It is the last five miles or so where the traffic gets really bad. This is nipping it at the bud. Otherwise the ironic alternative might be that the traffic downtown is from people looking for a place to park so they could use the great PRT system! That is one aspect of “short-haul” PRT that has always puzzled me – What does it really save if the passengers have to commute in to use it? (But then again I live in a city where almost nobody lives downtown)

It was recently remarked that PRT needed a network to be effective, that a simple loop or straight line would be a waste. Whereas this is largely true, especially compared to a large network, it is should be pointed out that even on a two-way straight-line configuration travel time can be improved by PRT’s off-line stations, meaning you can go non-stop to your destination, and the fact that PRT is available on demand. This cuts travel time to a fraction of light rail and a fraction of a fraction of bus travel time. In the case limited routing outlined above, though, many passengers would undoubtedly still need further transportation. The Achilles heel of buses is the many stops they must make, both for passengers and for stoplights. But even a very simple PRT loop could eliminate a huge portion of this wasted time. Personally, I wouldn’t like taking a five-minute bus ride to finish my commute, but I would do it if I had already saved enough time getting to the downtown area in the first place. If the last part of the journey were to be taken from a downtown terminal, however, (where an express bus would drop you off) that last leg might be and agonizing 20 minutes instead. I guess I am suggesting a possible symbiotic relationship between the downtown and commuter legs of system.

Finally I want to point out that the cheapest configuration for routing on freeway medians would be actually be a bottom supported design like Skyweb Express, because it would be so easy to construct low-rise track. This is not all that different from the cost/structural dynamics that enabled the spread of traditional railroads. For example, such track could be supported with gravel instead of deeply anchored supports. It is hard to imagine such a configuration costing very much more than a million dollars per mile. In most cases the Park and Rides have structures in place that could be converted into the required elevated boarding areas. In defense of hanging systems, I think they would be much preferred for these very large parking lots since they could pretty much come to your car.

Amortizing a million dollar a mile track is much, much easier than the inner city routes on which it would depend. (OK, it would probably be more, but I like round numbers) Consider amortizing the track over 10 years, with 33 cents per mile going to this purpose. Payoff is 3 million trips, 300,000 per year, or 822 trips per day. That is 34 trips per hour (averaged over 24 hrs) or about one every two minutes. Obviously they are mostly during rush hour, but equally obvious is that Holy-Grail benchmarks like two-second headways probably need not be reached here. More to the point is that a comparable HOV lane costs 5 times as much, and also the size of the parking lot needs to be considered. This may not be PRT’s “killer app” but keeping that many cars out of city center in the first place certainly seems like a worthwhile goal.

Finally, to my friends in the U.S… Happy Independence Day! This is a time when we can all come together and enjoy the sights and sounds that result from the enormous, ultimate, instantaneous release of CO2! :o) Oh well, be Happy. It’s the 4th of July!


Andrew F said...

Great post, Dan. I agree that some people erroneously believe that because PRT is most powerful as a network, it can't perform in a simple line configuration.

I was thinking about the ideal starter system, and one thing I was looking at was replacing suburban bus routes that feed into higher-order transit stations, such as subway or heavy rail. I was trying to look for one such route here in Toronto, if only because I know the city best. I identified a couple routes that are interesting because they have (i) highish ridership, at 15,000 trips per weekday and (ii) they have low fare recovery, at 50% or less (for a well-used route, this is low by Toronto standards!). If you're interested in some statistics, I found this report from the local transit operator:

Check out page 35, and look at route 45 Kipling. This route costs the transit operator $28,200 per weekday to operate, serving 18,300 rides. That's over $7 million per year in operating cost. The route actually overlaps significantly with 46 Martin Grove, and could form a loop. Since 46 is a new route, I needed to look at more recent statistics (2008), with 46 and 45 together serving 16,100+18,500=34,600 weekday trips for a cost of $33,900+$33,800=$67,700 per weekday, or $17.6 million per year.

This route could be served by a simple loop with periodic connections between them to minimize distance traveled. The loop itself would be about 30 km of single-direction guideway and perhaps another 5 or so km in connections joining each side of the loop:,-79.519386&spn=0.161347,0.338516&z=12&msid=115449720311537449338.00048a9cd3849b3973ded

Of course, a system this scale is not exactly small. But it does have a more or less guaranteed ridership base, and an existing operating cost that could be used to help fund it. The current operating cost could cover $283 million in capital costs at 6% discounting. Could we build a system in a suburban area at this scale for a bit shy of $10 million per km? I think so. Of course there is still operating cost to think of, but then I'm also assuming that ridership wouldn't improve and fare revenue wouldn't rise as additional benefits.

Something to chew on, at least.

Ryan Baker said...

Speeds almost definitely will be variable, but I don't think it's quite going to be a matter of preference. In a given area, I don't see much reason for much variation since there will generally be just one track. It doesn't require a track to be near full for a single slower vehicle to impede the progress of all other vehicles then.

The software can handle all that stuff, but I have a suspicion that the limiting factor won't be the software but the bureaucracy. Simply put, a system that isn't validatable on a napkin will have extra hurdles toward regulatory approval. In time those barriers will dissolve, but not right away.

One last note.. I don't think it will be necessary, but honestly I would trade a 45 min drive for a 65 min PRT ride. Thats because I could read for those 65 minutes and it would be safer.

On cities vs. suburbs, or network vs. loop vs. corridor, I think there is definitely a sweet spot in citywide networks. However, those are in general a very tough nut to crack. But since they are so sweet they are kind of like a pinata, land one city and the rest will fall out like candy.

The suburbs are more like an easter egg hunt. There are many suburbs and none are really that big of a prize, and finding one doesn't help all that much to find the next, but on the other hand, and the opportunities in the suburbs are all well hidden because you need to find the oasis within the quagmire in which any modest system can compete with the already established car.

On the other hand, there are lots of those suburbs, and as a result plenty of easter eggs so if you keep trying you're have better odds of finding something that the other kids missed.

In the other thread there was mention of Nathan Koren's paper, and a couple other suggestions that PRT proposals should steer clear of places LRT is working on a proposal. While I understand the idea that it's better to find an uncontested niche, I think it's important to realize that PRT has to do more than find a place uncontested by LRT to be in an uncontested niche, it would also have to find one uncontested by the automobile. There are not so many of those.

To me this means that PRT is going to have to compete with someone long before it's been developed to the point of self-sufficiency, and for various reasons I think it's easier for PRT to compete with LRT than it is to compete with the automobile.

For one, the organizational structure required to run a PRT project has more in common with LRT than the owner-manufacturer-highway department structure of the road/automobile system.

Anyhow, almost anywhere the automobile has failed, someone is going to be proposing bus service, BRT, LRT, heavy rail or something.

Anonymous said...

In my opinion ideal starters are on the one hand airports, on the other hand projects like these:

Then there are new development suburbs, my home town has a couple such projects where PRT would indeed make sense (for one of them, government's actually appointed a study group:ÖKSY

(only in Finnish, don't press the 'in English' flag)

To me, the concerns Dan brought out in this post seem unnecessary. Yes, some people have historically thought of PRT in that way. But the actual transport planning section - at least in Europe - is rather new to PRT and does not have mental obligations one way or the other. If it works, they'll use it. We will need quite a lot of educating though, to make planners utilize PRT the way it should.

Andrew's sample from Toronto sounds exactly as such a case. We just need the Product.

This is at least where we are aiming with BM Design.

Ryan Baker said...

Large airports are good enough, but how many airports are large enough that anything more complicated than moving walkways are worth it if the system goes no further than the parking? 20 in the U.S., 100 Worldwide, and a number of those already have something in place like a monorail or something similar. Of those that remain, you have to be lucky enough to be approaching them at a time when they are open to spending money and starting a new project.

That list could be expanded by targeting airport campuses. Even the smaller airports tend to have some reasonable degree of nearby commerce, and cities would be happy to see this become more attractive as a place to conduct business and thus expand their tax base without putting a strain on other city services.

Without a campus, even the large airports are only "okay" in terms of taking advantage of PRT. They are good because they do have all hours traffic (an area in which anything automated has an advantage). They also have large quantities of traffic. But the network effect is some muted. For the most part passengers are going from the entrance to the gates, so straight-line services. In very large airports there are plenty of transfers but even there that's 30% of passengers at best, and most of those transfers aren't in different sections of the airport.

Anyhow they are good enough to get positive value, but I wouldn't say they were ideal.

Ryan Baker said...

Hmm.. I think some of my comments have been a little negative, I don't mean it that way.

I think I am trying to make the same point from a different angle.. don't count any opportunity out. PRT has so many superiorities that even in the non ideal conditions it offers real benefits.

Right now it's not about finding ideal opportunities, it's either about finding opportunities with few roadblocks or finding so many opportunities that your bound to find one where luck is in your favor (and luck can be as simple as one favorable politician or influential resident).

Dan said...

Andrew; Thanks for the post and the research. I wish I could say I’ve had the time to really take a close look. I’ve mentioned many times that I really should be doing other things besides even writing this blog in the first place. That being said, I have questions. First, how long are these routes? It’s kind of hard to work the math without knowing how much the passengers are paying to go how far. Then, what is the passenger experience on these routes? How fast do these bus systems get you where you are going? At less than a dollar per trip it certainly is priced right. How many vehicles would need to operate on how much track, and how many stations would be needed? Buses typically stop on every block. Would passengers walk further for a faster ride? What kind of speeds would the PRT system need?

Ryan; have you read some of the FUD that the light rail spin-artists put out? It’s pretty darn convincing to anyone not totally familiar with PRT. Cars, at least, don’t fight back. Also, it’s quite easy to find routes. Just look for the slowest traffic, and places where it is slow because the road has already been widened as much as there is room for. That forces the issue of raising any type system off the ground, and that puts PRT’s best foot forward. Most of the cost of PRT is in stations and installing supports. The freeway routing could cost 10% of the inner city routing but requires that inner city routing to be useful.

As per the Airport thing, that would be fine for a very inexpensive system. There are often remote parking lots, and I would wager that many people would rather be picked up at a local eatery, especially in very busy airports, or perhaps it could also go to nearby hotels. I say inexpensive because the system wouldn’t need to be especially fast or smooth, and I’m not sure that the traffic volume would be all that great. It would certainly be handy for the small, steady stream of passengers who would use it. I am assuming here that we are not talking about connecting with downtown, since that’s usually pretty far.

Akauppi; I am a bit confused as to what you mean by “We just need the product.” What shortcomings, specifically, do you wish to remedy with your designs? Anyway, you are lucky that people in your part of the world have more open minds to this kind of thing. I really doubt America will ever lead in PRT, unless it happens long after it is widely tested in real-world service elsewhere. By the way, that Italian designer sure would have some explaining to do if someone funded his vision actually thinking that such structures and vehicles could be built as shown. The track is too thin to even support itself, and rests on skinny little supports that would just fold. The vehicles seem to have no propulsion or levitation means, nor a power supply nor batteries. Just the air conditioner for such a greenhouse-like vehicle would be huge. Not to mention that he seems to think he can just go drilling into those old bridges for support. I mean, what is the point in getting everyone excited about designs that can’t possibly be built or comply with safety codes?

You guys all remind me to extend my imagination beyond the sprawling U.S. Sun-Belt cities, where I have spent most of my time over the past years. Moving around a pedestrian-rich inner city would seem to require a less robust vehicle than higher speed commuting. The question remains though, what happens if an inner-city system grows until it has real distances involved? Some will have no problem with a slow system. They will just do some work or read book. But try selling that to parents paying for childcare instead of having a home life. To them every minute traveling is a precious minute wasted.

Andrew F said...

Hey Dan, no worries. This blog shouldn't be a burden. I like it because it lets me think about something pretty different than what I do professionally.

The two routes I mention are about 13 or 14 km long, running parallel north-south about a kilometer apart. At the south end, they funnel into a subway station (the terminus of the line) and a commuter rail station. There is another commuter rail station about mid-way on one of the routes. If I had to guess, I'm guessing the average rider is travelling about 6 km. The cash fare is $3, transferable to the subway system, but not the commuter rail. The buses can average about 21 kph. I think there are about 50 stops on each line. I think they could be spaced a bit further apart, should that be necessary.

My estimate for how many vehicles would be needed is based on 80% of trips at 1.5 person occupancy taking place during rush hours, of which there are 90 minutes each in the morning and the afternoon. This gives about 6,000 system trips per hour. Assuming 50% empty travel (to balance vehicle flows) and 6 km average trip distance at, say 60 kph average speed, a vehicle can serve 6.6 trips per hour. thus we'd need about 900 vehicles at peak, without promoting ride sharing.

Of course, I only used these routes to get a sense of what was possible in terms of ridership in a real-world situation of replacing a bus route. Perhaps a smaller loop (same terminus at the south end, but doesn't go as far north) would be more advantageous. These routes are also pretty close to the airport, and could easily connect to a system serving it and the surrounding hotels, etc. I'm curious of what you think a system using your paradigm might cost in this kind of environment (suburban 4-5 lane steets, buildings set back from the road). If you allow $40k per vehicle for 900 vehicles, you get about $1.2 million per km. If you have supports every 15 m or so (which seems to be the spacing for the light standards) at what, $50k each, installed? That's another $3.3 million per km. If you allow $2000 per m for the guideway and truss, that's another $2 million per km. If stations are $350k each and spaced every 300 m you get another $1 million/km. This gives us $7.5 million per km, plus any additional infrastructure costs. I have no idea if these costs are reasonable. If ULTra can do it for $5 - $10 million per mile with their heavy guideway, I'd think it should be possible to do it for even less than that with a better designed system.

Ryan Baker said...

I don't think all the FUD is from light rail advocates. I've received just as much negativity from die hard car people. I've heard a lot of FUD over the idea of anything automated. I've heard "freedom" stuff about how it's so important to be able to drive 90mph while tailgating and texting. I've heard "creepy".

Cars fight back in the way they operate, lots of little inefficient contributions, but it's everywhere and it never stops. Cars fight back against light rail too, and so light rail only goes to places it thinks it can be successful. And unfortunately the characteristics that make an area favorable for PRT winning a battle against the car culture also make it favorable for Light Rail. PRT is more flexible and as such there is a gap. But add in some of the "first timer" obstacles, and that gap can be as difficult to fill as competing directly with LRT would be.

Once those obstacles start to disappear though, then PRT will win the gap and the top quite easily.

cmfseattle said...

"The guideway was sized to permit the demonstration of constant speed operation, slot slipping and slot-advancing maneuvers, merging, switching and emergency stopping. The nominal operating velocity for the scaled vehicles was 3 feet/second, representing a full-scale velocity of 30 feet/second."

From this, I can see how there has been some misunderstanding... however: "slot slipping" is when a vehicle slows in order to allow another vehicle ahead to merge. "slot-advancing" is when a vehicle speeds up in order to accomplish same. Therefore, the line speed was in fact variable. (Also, if you watch carefully at the beginning, you can actually see the some of the "vehicles" changing speed in order to open up "slots.").

ULTra currently uses a "synchronous" management software design: vehicles don't leave the station until their entire journey has been reserved (no conflicts). So, if a vehicle isn't where it's supposed to be, when it's supposed to be, there's a problem.

In asynchronous designs, vehicles only have to wait for a merging opportunity. During peak traffic, the line speed could be reduced or vehicles would clog stations. (But at least there wouldn't be aggressive types who dive into merges at the last possible moment, resulting in even more congestion for everyone following).

I've found Ian Ford's Routable Transit Network Design to be good food for thought.

Anonymous said...

Dan: What I meant by "we just need the product" was for PRT industry as a whole.

By sellable I meant something like Siemens, Bombardier would be offering (though not necessarily those companies). Communities don't want to be guinea pigs; let alone support some noble thought that might or might not work. They need a riskless solution where performance and costs are calculable. Business as usual. Such a PRT product does not exist.

About the Rome case. I agree with your criticism, but the generic idea of using PRT as a *component* of Tiber river side revitalization is in my opinion valid. Ultra has done their share of similar concepts for the city of Bath in UK, as I'm sure you are aware of. They are more realistic.

p.s. Your comment on July 8th is saved twice. Can you delete the latter (which is a subset, though timed 1 min later).

Dan said...

Dan the Blogger Responds in two parts…

Andrew, that tells me a lot, especially the part about the interface with other public transportation. It appears that there are significant non-auto transit choices in Toronto, which bodes well for PRT because people can actually get somewhere without a car. While you are a being a pedestrian you are not being a driver! PRT has traditionally been designed for such pedestrian rich environments. I must say, though, that on my virtual walk-about on Kipling Ave. it was pretty devoid of people. (wrong Kipling?) Anyway, feeding traditional mass transit has always been a winner for PRT in my mind. It brings up a different aspect of the “network effect,” that being the potential amplification of PRT’s effectiveness by means of other forms of transit.

In Houston, by contrast, there is only one 8-mile two-way stretch of non-road-based transit (light rail) serving its 600 square mile (1600 square km) area and 2.3 million citizens. (I doubt even 4000 people live within walking distance of the line) Most of the people, however, (an additional 3.6 million) live in the much larger (9000 square miles) greater metropolitan area, and commute. The reason I bring up the need for a commuter capability for PRT via freeways is because there is little else to leverage. Those Park & Rides are the only places where people leave their cars behind.

I recently saw a “Frontline” documentary on TV that compared a city like Houston, (Tyson’s corner) with nearby, pedestrian friendly Arlington, VA, which is emphasizing its rail system and mixing residential and commercial development. If you are interested in the segment , it’s “chapters” 12 and 13 – scroll to 1:35 seconds into chapter 12, unless you are cmfseattle, since the preceding segment is on Seattle and the Puget Sound)

Dan said...

Ryan; I just am still just amazed by the craftsmanship of the PRT Keeps Colliding with Reality piece. The subtle use of negative adjectives – the strategic selection of facts – the half-truths – the omissions - the raising of non-issues or issues specific to a single design as though it is a generic problem. It’s a very pretty piece of spin. Pure crap, but well crafted. True, car lovers or (anyone else who thinks there really isn’t a problem) will spread FUD as well, and they are more numerous. They are just not as organized or well financed. I would particularly avoid using proposed light rail routes as examples of wasteful spending compared with PRT. Any public transit beats cars and can benefit PRT by making pedestrian travel more viable.

Cmf, did you catch that piece on Seattle’s storm run-off? Anyway, that IS a pretty good paper on routing. I’m not sure he would feel the same way about 2-way track if he were working on a suburban sprawl model instead of Albuquerque, however.

About the variable speed thing… I never really considered bumping up a slot or back a slot as variable speed. That’s just line-speed plus or minus “x” To me real dynamic speed control is where (for example) it’s too late for a merge unless the vehicle can speed way up to catch up with the vacancy. It would be where vehicles would go faster on straight-aways and slow down for curves, traffic permitting. It would be where vehicles speed up to clear a segment to benefit heavy traffic coming from behind. It’s where the vehicles can behave like suspended particles in a piped fluid responding to pressure. They can move faster in response to traffic volume, and can disburse, distribute, or aggregate in ways that maximize throughput while still considering each passenger’s comfort.

Akauppi, They said my comment couldn’t post but then posted it anyway. I actually deleted 2 others and that one got through. I guess even Google goofs sometimes. Fixed now though.

Ryan Baker said...

Dan, don't underestimate the car groups. Talk to a light rail advocate about what their opposition is. Light rail advocates are spending most of their time trying to convince the government to spend money on LRT while the other lobby is asking for more highways.

It would be very useful if PRT and LTR advocates were more collaborative, since ultimately both have similar objectives. You are saying some things similar to that, but I think there is a better way to do that than intentionally avoiding all competition.

In the realm of competition, a big possibility is the robotic car. See this for some tracking of progress on that front.

PRT has advantages over robotic cars, but if robotic cars get a foothold it's going to be a tougher battle convincing others of the value of lighter weight, elevated vehicles after accident rates have dropped, traffic has been improved (though maybe not solved), and people no longer have to manually navigate the traffic.

Andrew F said...


Toronto has pretty high transit ridership by North American standards. Ridership per capita is second only to NYC. So yes, even on seemingly desolate suburban thoroughfares like Kipling we see decent ridership levels. I suggested Kipling because it is a street that is not currently slated to get LRT. There are some even juicier routes that are slated for LRT, but I would be skeptical as to whether a starter PRT system would be able to handle that load. I think even the established load from the Kipling/Martin Grove loop I suggested might be a bit high (I'd think it should be phased in, perhaps with another set of north-south guideways for added redundancy). And considering how poor bus share is as a proportion of trips, I suspect ridership could rise significantly with PRT. This area, being on the boundary of the city proper, is not currently very well served by transit. In fact, if you look slightly to the west along the highway 427, you'll see some pretty high density development (the census tracts there have density over 5k per km^2/13k per sq mile). Lots of very low hanging fruit in this area, in my opinion, but under-served because it is on a political boundary.

Andrew F said...

The paper cmf linked to was very good, I though, except his conclusions about two-way networks. I can see the value of more coverage per dollar with single-direction infrastructure, but eventually capacity concerns will make less circuitous trips appealing because they free up the vehicle faster and consume less guide-way space. I think there are a couple strategies he missed for addressing bidirectional networks because he dismissed them so quickly. It is the left turns that are costly at intersections, and a right only intersection could be done on 2 levels with essentially no added complexity over one-way networks. You could accommodate left turns by sparingly adding some 'u-turn' sections away from intersections and in locations where they are advantageous from a network perspective. Essentially a siding that would slope up and allow the vehicle to decelerate, make a slow, very tight turn, and accelerate down to the opposite direction of original travel. Most trips could be accommodated using only right turns, without undue delay, so these could be used quite sparingly.

As far as opposition from various interest groups, I'm not sure why PRT should have enemies in car proponents. Car interest groups generally oppose surface transit, and especially BRT/LRT, because they compete for lane-space. So in a situation like Tyson's Corners, it seems to me that car interest groups ought to support PRT where they concede transit is necessary. A circulator bus or LRT would take away valuable lane-space. And either transit service would likely need dedicated lanes and priority signalling to be very effective, and these things make drivers steam, as they see a bus whiz by while they are stuck in traffic, and they eye the lane that seems underutilized (even though it might be carrying more people than the normal traffic lanes).