Sunday, May 9, 2010

85> The Enemy of the Good


I just wanted to expound a bit on the subject matter that was touched on in the comments section of Post 82. The conversation centered on the pros and cons of the ULTra system. (Actually mostly cons, in regard to weather, speed and aesthetics.) One statement by alert reader Bruce, in particular, got me thinking -  “I think it would be rather more regrettable if the perfect were allowed to become the enemy of the good. The ULTra design is quite good enough for a wide range of transit applications.”

This has always been a worry of mine. As one who is probing the possibility of a standards-based design architecture, I am particularly averse to imposing arbitrary limits on those standards. The fact is, though, that if I had real-world budgets, deadlines and targeted customers, I, too, would have to dial back the system capabilities to get the job done. I do not want to create unrealistic expectations in regards to what I am doing or cast doubt on present systems. In other words, I do not want to be the “enemy of the good.”  On the other hand, there is also the possibility that the “good” could become the enemy of any and all PRT, if it doesn’t measure up to expectations.

PRT used to have the advantage of being the only practical way to move individuals and small groups electrically. Battery technologies have changed that. Now we can expect the door-to-door convenience of a private car with the energy usage formerly attributable to PRT alone. Suddenly PRT has something else to compare itself to beside gas-guzzlers.

I believe a very strong case can still be made for PRT, but some embodiments make the case better than others. Recently this NY Times article was posted on the Transport-Innovators site. It illustrates how damaging it can be to choose the wrong PRT system for a given implementation. This has given a black eye to all PRT. The layman will read this article and assume that the PRT concept was proven unworkable. At the very least, they will take away that it is “buyer beware” when it comes to PRT. In actuality the problem wasn’t PRT per se but more with what this design was to ride on… pavement. If we lived in a paved labyrinth of levels and ramps, relatively slow robocars would be an excellent choice. But in a 2D world of limited surface area, pavement riding PRT designs must compete with electric Scooters, Segways, bicycles, pedestrians, regular electric cars, not to mention gasoline powered vehicles. Is PRT really the best use of pavement? If so, by what measure? Energy usage? Passenger throughput? Time to destination?  Will it remain that way into the future?

There was a time when one main object, it seems to me, was to free up the pavement to reduce traffic and get a bit more green space. True, pavement roving PRT vehicles are smaller than the average car, so the track for such vehicles is more economically elevated. But such track could also be used productively by opening it up to ALL small, motorized vehicles. This would encourage downsizing.

At the risk of getting sidetracked, I wish to reiterate the point about being smaller and therefore more economically elevated. This is no small deal. All ground -based travel, from pedestrians to supertankers, is subject to interference based on differing directions of travel. That is a fundamental fact of 2D travel. The fact that ordinary roads must sometimes support very heavy trucks makes overpasses, (the non-stop solution to 2D interference) much more expensive. Nevertheless, making them anyway has revolutionized our way of life and greatly increased our prosperity. Imagine, for a moment, turning back the clock, and replacing all of the freeway overpasses in your town with stoplights. This would effectively draw many cities to a halt. This is a revolution that has not come down to the neighborhood level, however. We all still pay homage to the good old red light.

PRT carries the promise of cutting through the busy urban landscape like nothing ground-based ever could. With a system like Ultra or 2getthere, there is the flexibility to have
the system either ground-based or elevated. Ground based is cheaper, and so has that as an inherent attraction. Both companies point this out. But when once you consider that the track must be fenced, and that it will block any cross traffic from pedestrians or other vehicles, this becomes a false choice. It seems painfully obvious that this is partly what the designers at Masdar are now discovering.

 Another promise of PRT is (like most automated systems) to achieve speed by eliminating human error. But we have become accustomed to dangerously small headways between very fast moving vehicles when it comes to cars, yet are extremely unlikely to ever allow such headways on automated systems that rely on simple tire traction to steer and stop. This is especially true considering the possibility of wet or icy pavement. So this promise, too, of PRT is unlikely to ever be realized in such systems. The system’s users will have to be content to go at school-zone speeds for the entire trip.

True, these problems are of little consequence for applications like airports or campuses. Creating a profitable business model around these platforms would seem to be a positive first step for PRT.  But many people are holding these systems up as the urban/suburban transportation of the future, using arguments borrowed from faster, all-elevated (and sometimes purely theoretical) systems. Somewhere in the definition of PRT is the implicit supposition that the system is a viable means of urban transportation. With top speeds that are 10mph less than the current speed limit for un-posted city streets, I really have to question that, at least for the sprawling cities I know. I very much worry that such a system will be tried and then fail to live up to expectations. Imagine what the folks from light rail would say then.

6 comments:

cmfseattle said...

Batteries for long, level stretches and sliding contacts for slopes.

afransen said...

A few things:

-even with all-electric drivetrains, cars will continue to be expensive by virtue of the fact that the infrastructure is very expensive, the vehicles are heavy for crashworthiness, and congestion limits average speeds in urban environments.
-automated cars are pure fantasyland, at least for the next few decades, for the same reason why we can't have ULTra level crossings at grade: traction in adverse weather conditions and the insurance required. I also am skeptical AI can supply vehicles with the level of reliability that vastly surpasses human operators in these kinds of conditions.
-We shouldn't allow the 'okay' to be the enemy of the 'good'. We have seen this in other areas, with the modern social welfare state being built on income taxes and welfare, when there are better models available. We are stuck in a bad equilibrium, where the system works after a fashion, but there is a better equilibrium that could be reached with sufficient political will. I suppose the same goes with the electoral system we use in much of North America (first past the post).

Dan said...

Dan The Blogger Responds-
Not a lot to add, guys, other than to say I'm watching the progress on the battery/capacitor combos very closely. Being able to dump a lot of power into a vehicle's battery as it passes would have obvious advantages for PRT! Expect a post about it soon.
Alfransen, half of the bad equilibrium is having a population that is so conditioned to appreciate cars. After all, it's pretty nice to drive a fine sports car on a winding, scenic road. Until the pavement, pollution, noise and traffic totally take over where you live, it's pretty hard to recognize the self-destructive nature of the automobile/fuel/roadway system. It is a shame that this system rewards excess fuel consumption with speed, control and status.

Bruce said...

I agree with the point you you start off with, that a bad early implementation could harm PRT, but I still think you're being far too harsh on the systems you mention (ULTra and 2getthere).

One of your complaints is that 25mph is too slow to be useful. Actually, at 25 mph, these PRT systems can claim to be among the fastest urban transit systems available. Average trip speed is what counts, not top speed. Buses in cities achieve an average trip speed of just 8 mph. Light rail manages 17 mph, and metro rail gets you there at a blistering rate of 20 mph. In most cities, automobiles average less than 25 mph; in some big cities, it's more like 11 mph. By comparison, then, these PRT systems are pretty quick.

Various studies, as well as ULTra's experience at Heathrow, suggest that the ULTra system is cheaper than both light rail and bus for a wide range of applications. It's also cheaper than the group-transit APMs that are common today in airports. If it's cheaper than existing transport systems, and at the same time faster and more convenient for passengers, even if it does not represent the ultimate in what PRT can potentially achieve, is it fair to say it is not good enough? I don't think so. Perhaps you disagree.

You suggest that Battery Electric Vehicles are now good enough to make PRT (or, at least, the ULTra and 2getthere designs) redundant. I am sure this is wrong. Batteries are still too expensive, the range is nowhere near adequate, and convenient charging is not available, therefore BEVs are not yet competitive as a means of day-to-day family transport. With a huge investment in battery-swap infrastructure, they might become so, but it will take a while. The ULTra and 2getthere vehicles are battery-powered, but convenient charging is designed into the system, and the uninterrupted traffic flow on the guideways is good for range, so they have a big advantage over privately-owned BEVs operating on city streets.

You say that ULTra and 2getthere can operate very cheaply at grade, which in itself is a good thing - they can go at grade, but they don't have to. There are situations where this can be an advantage, so the fact that it can do this is not a point against it.

Any PRT system, regardless of the guideway design, could in theory permit private, non-PRT vehicles to enjoy unrestricted access the PRT's ROW, but this would be stupid in every case. The weird negative statements from Masdar about PRT, since they make no reference to any problems highlighted in testing, or even any theoretical problems with PRT, but only complain that cars are excluded from the city, which makes it sound as if the person speaking hasn't really understood the masterplan. I think, therefore, that the statements can be ignored. What will matter is not such statements, but how well the operational testing, due to start this month, goes. Meanwhile, the Heathrow system has been in operational testing for more than a year, and is due to go into public service next month.

The great thing about having two pioneering projects on the go at once is that neither is critical by itself for the future of PRT. If one fails but the other succeeds, PRT is still okay. I think there are good reasons to expect that at least one of the systems will succeed, and I'm especially confident of the ULTra project, as they seem to have tested everything testable, and taken a cautious approach from the start. What nobody knows yet, and what ULTra will discover soon, is how the public will behave with these vehicles in an actual service environment.

Dan said...

Dan the Blogger Responds-
Thanks for crafting such a thoughtful and researched comment, Bruce. You make some very good points. Your comments remind me of something I written about in the past, that cities are very different and have differing transportation needs. Part of the reason I have reexamined and redesigned PRT in the first place is partly because the current offerings are illsuited to the transportation needs of the cities I frequent. In particular, most offerings are designed to get around a city’s central business district. This is not really an issue in newer cities that have grown outward along their freeways. These cities don’t have much going on downtown, and do not have many pedestrians or destinations for them, except for the lunch crowd. The shopping and entertainment occur in satellite communities.

This environment requires PRT that is designed for longer distances and lesser pedestrian densities. The “robocar” PRT design seems particularly ill suited for this task. Of course being so closely related to “drive-by-wire” automotive designs has other advantages, and I won’t knock the business strategy. I just wish that the people introduced to PRT by such systems didn’t get the idea that the PRT concept is defined as robotic cars on paved roads. I am afraid that this misconception will, in the minds of many, place PRT outside of consideration for that large proportion of U.S. cities with suburban sprawl. They need PRT as badly as anyone.

As for electric cars, I am perhaps a bit ahead of the timeline, but I can see the writing on the wall. After all, by the time any new PRT contracts are inked, a lot will have changed.
Chevy is introducing the Volt. Nissan, the Leaf. Tesla is taking orders for a sub 50g sedan that goes 0-60 in 5.6 seconds and has a three hundred mile range. Warren Buffet bought 10% of a Chinese battery maker turned carmaker, and they will be start importing within a year. There is another Lithium battery maker in China that is on the same page. Both are getting huge subsidies. Battery prices continue to drop. Meanwhile research continues on “supercapacitors” which enable ultra-fast charging. Coleman now markets a screwdriver that can recharge in 90 seconds.

I should also mention a case where ULTra, would, in theory, be just what the doctor ordered. That is the mega retirement communities known as “Sun City.” Here seniors need a way to get around and what do they use? Golf Carts. A quick trip to the GEM web sight will reveal vehicles that are the functionally similar to ULTra/2getthere except they are human driven. Such vehicles are also common in Florida Golf communities. Would these users want to switch to automated vehicles for the price being asked? Remember that these vehicles don’t require any fencing to run at ground level, and I also believe they are street-legal in many states.

As far as Masdar is concerned, I understand it has been scaled back to the point of near irrelevance. I am afraid that the main impression that a visitor will get is that the guideways can’t be crossed. If I get it right, the PRT is on a basement level, or at least not overhead. Crossing the guideway has always been a problem for systems with constant, automated traffic. Not elevating it is, well, not exactly putting PRT’s best foot forward. Hopefully it will turn out to be a good showcase anyway.

Bengt Gustafsson said...

Yes, Masdar PRT is at basement level, which is physically on ground, but all streets are decked over at about 5m so the impression for the visitor is that the PRT (and heavy trucks when needed) is in the basement while walking and biking is on the open level.

I don't think they will scrap the PRT, but the buildout of the entire Masdar will be much slower than planned. The reason for this belief is that they would have to replan everything to scrap the PRT: There is absolutely no room for parking anywhere in the city. With parking added the entire planning falls flat: The narrow streets become significantly wider, which is a bad thing when you want to deck them over. Also they want narrow lanes on the open level to let houses shade the sun. So I would say that either Masdar gets built as planned (eventually) or it doesn't get built at all.

One aspect which could be of importance is: Do people want to live with their car parked a mile away. Or even if they would if they tried it, would they think so beforehand -- when buying the house?