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!
