Wednesday, October 28, 2015
In the last post I referred to PRT as a kind of “Urban Wormhole” and spoke of how self-driving taxis could never replace PRT. I would like, in, this post, to follow up on that a bit. I think it is important to make the relevant arguments clear and on the table for all who will listen. An entirely new and untried transportation infrastructure is a tall order, yet I believe there are unassailable arguments why such an augmentation to our current systems is necessary and inevitable. I have included a short quiz in this post, designed to (hopefully) win someone over. Now, if I could just come up with a really catchy slogan….
The robotic car push reminds me of that stage of the internet revolution that centered on perfecting the dial-up modem, which of course, can only be as good as the phone wires it is connected to. In the case of mobility, at least in urbanized areas, the main problem is that there is an inherent cap on our surface transportation’s efficiency. It is, at best, 50%. The reason is simple. Simple physics dictates that if 50% of traffic wants to go east/west, and the other half wants to go north/south, each will have to yield right-of-way 50% of the time, once a line for each direction has developed. Nothing but passing over or under that crossing traffic can improve this dismal number. And that is the best case for the intersection itself. Were we to measure efficiency based on the time difference between “making the light” in no traffic and what can typically happen in rush hour for individual cars, that efficiency number would be much, much worse… 15 – 20% perhaps? And that is only one, and they add up! In what other endeavor would we put up with such inefficiency?
This is all unfortunate because, with the possible exception of bike trails or sidewalks, there is no current surface transportation infrastructure that can be elevated or buried economically enough to generally allow multi-level, non-stop traffic flow. If it WERE economical, we would not have such gridlock today!
Vehicles, and the surfaces constructed for them to roll upon, (this includes rail) have evolved to be too big, cumbersome, and expensive to be the only alternatives in space constrained, urban areas. How ironic that, in a quest for the efficiency of carrying more load per vehicle trip, we have accomplished exactly the opposite! In all fairness, bigger really IS better, once you get out of town a bit – yet gridlock is the elephant in the room when it comes to urban mobility and robotic cars can only be of peripheral help in the current context. Any real solution demands an infrastructure specifically designed for non-stop travel in all directions at once, and logic dictates that this architecture be smaller, not bigger. The fiber optic cable of transportation! Actually, it is within this framework that automatic driving technology can really shine. With a faster, yet smaller “pipeline” the driving decisions would come at a much faster rate as well. No place to be texting!
So here is the quiz. It is more for making people think and to stimulate conversation than anything else. Maybe it will help win a few converts!
1] Non-stop ground transportation can only be achieved by incorporating overpasses/underpasses but this is impractical for widespread use because of the heavy loads that our current roads and rail systems are designed to carry. True/False
2] The majority of vehicles on the road are carrying payloads, including people, that weigh just a tiny fraction of what roads are built to carry, and this represents a waste of resources if more appropriately scaled infrastructure is possible. True/False
3] The ONLY way for most travel to be non-stop within an urban/suburban environment is to create a new, more affordable infrastructure which is necessarily aerial and sized appropriately for lighter payloads, such as people. True/False
4] The technologies for automatic vehicular and traffic control to utilize such an infrastructure have now come of age. True/False
There. Saying “False” to any one of these will hopefully start a thoughtful debate at least. “Grass roots” movements have to start with consensus, and consensus must start somewhere!
When I started this blog, part of the mission was to create some standardization, particularly with regard to the track. Seen in this light, it can be better understood why so many PRT bogie/track designs have been explored on this site. The world needs an infrastructure for urban/suburban mobility that allows non-stop travel. Dual-mode? Fare based? Privately owned? In a way it really doesn’t matter. To me the question is, “What are the mechanical/architectural underpinnings that will best encourage the development and proliferation of such a system?” We need the combination of present practicality and boundless future possibilities if we want to propose it as a solution worthy being added to skylines across the globe. I believe a PRT track can be designed that includes very little beyond the architectural structure that is required for spanning between support posts. Sort of a standard PRT building block, which (as most of you know) I have dubbed the SMART (Suspended Multi-Axis Automated Rail Transport) platform.
A brief progress report is, perhaps, in order. In the design pictured up top, I have continued with the theme of using off-the-shelf-parts, and experimented with putting the four motors between the drive wheels instead of off of the ends, and this shot highlights a new cam-driven lever-type switching-guide-wheel mechanism.
Right this minute, the holdup is this – I love the idea of being able to remove the side of the track that normally switches off (right if you are American, left if you are British) without diverting PRT traffic. This would allow switches to be added or removed with minimal disruption in instances where no alternative routing exists, such as is likely to happen again and again on the outer edges of any growing network. Unfortunately this entails running on the left wheels alone and doubles the load on them. If the wheels are to be soft enough to cushion vibration and smoothly handle expansion joints, and especially if they use ordinary, safety-rated pneumatic tires, they will compress under the load and maybe even deform side to side, adding substantial complication to what could otherwise be a super simple switching scheme.
In these last two pics first note that the steering wheel guides have been turned upside down (compared to the one on top) and there are no longer two sets per side, like in previous posts. It looks like this would be sufficient, even in this "half-track" mode, if we wanted to use custom solid tires designed not to rock or compress too much. Unfortunately I would like to make this cheap and straight forward enough for an individual, company or university to build for experimental purposes…, hence the “off-the-shelf” trailer tires. (Smaller, higher pressures and stiffer sidewalls than automotive)
Finally note how the track’s spine is missing the opposing C channel, since that side has been removed. That otherwise sandwiched plate is a splicing means, a potential hanger for cable stays and placing an upside down “U” channel over it can create a waterproof seal, like in a standing-seam metal roof, when used with the sheet metal sheathing, which is curved to stiffen it between structural ribs. Work continues!