With the various advances that have come to transportation
lately, PRT has lost its monopoly on many of the virtues that once made it
unique. It is, perhaps, natural to wonder if PRT’s time has come and gone. Once
upon a time only PRT could manage its traffic because the vehicles were
centrally controlled. Now, with traffic apps, roadside electric billboard
alerts, etc., drivers by the thousands can increasingly be alerted of upcoming
congestion and change their routes accordingly. In the very near future cars
will be “talking” to signs, traffic lights, the cloud and to each other. In the
past the whole idea of a driverless vehicle was unthinkable without a dedicated
track or guideway, simply for safety reasons. That is clearly changing. Once,
PRT alone made electric vehicles practical, because an electrified rail
eliminated the need for the heavy lead-acid batteries that made electric cars
slow and short-range. Another advantage gone. Does all of this mean PRT is
dead? Can PRT’s essential advantages can be had in different ways? Let’s dig a
little deeper.
One must first realize that progress has not been confined
to cars alone. PRT’s centralized control scheme was a liability as well as an
asset – A single glitch could strand everybody. Autonomous driving benefits PRT
right along with automobiles. This is especially important in that it facilitates
variable speeds which, in turn, enable tighter turns and faster straightaways,
making PRT much more versatile. Those sweeping, graceful turns once depicted in
PRT promo material were far from an asset – who would give up their valuable
corner property without a fight? Advances in batteries benefit PRT as well. Now
there are many “third rail” options including none at all, being a discontinuous,
a charge-on-the-go system, supplementing solar collectors, etc. Wireless
connectivity, combined with more “intelligent” PRT control makes for a very
robust and fault-tolerant system. In other words, any PRT system that is
devised today can be far superior to past designs by almost every metric.
Although many designs still represent a basically workable,
even elegant transit alternative, enough has changed in the technological
landscape to justify a re-think of many key aspects of the whole proposition.
It’s not just self-driving technology and batteries. It’s smart phones, the
cloud, how things are prototyped and manufactured. The world itself has
changed, including people’s expectations and behavior. About the only thing
that hasn’t changed is the need. The fundamental problem with “surface”
transportation is that paths inherently cross, leaving no alternative but for
someone to stop and wait, whether you’re a pedestrian, train, on bicycle or on
horseback. The large size and weight of commercial vehicles on our current
roadways curtails extensive use of curative overpasses and even when elevation
is absolutely necessary, the high inertia of these vehicles is such that
massive cloverleaf designs must be created or they would simply skid off the
road at reasonable speeds. This, with the shrinking amount of available ground-level
space, ensures troublesome bottlenecks. Self-driving cars, alone, can never
solve this dilemma. Private passenger vehicles do not require anything close to
such a heavy infrastructure, yet they comprise the lion’s share of vehicular
traffic. There is, therefore, great advantage to be gained by giving such smaller
vehicles a modern, non-stop infrastructure all their own, which can also
eliminate the need for plowing, policing, and save lives. So if a smaller
gauge, elevated (and presumably automated) system for moving people is still needed
what, specifically, has changed?
PRT has always been a mix of utopian dream and practicality.
You walk a short distance to a station, there are private vehicles waiting, and
you get whisked away, non-stop, to your destination. But wait: A “short distance?”
How short? “Private vehicles waiting?” Every time? Isn’t that kind of wasteful,
having that much precious investment sitting idle? What about vehicle capacity?
Should all vehicles that will usually carry one be built for four, “just in
case?” And what about “non-stop?” If a vehicle can pick up a passenger or two
without adding substantially to the travel time, isn’t it kind of inefficient
not to? Or what about “To your destination?” How close are we really talking
about? Above all, is this practical as a business?
Unfortunately, the whole notion of PRT becomes very iffy
when many important stations have yet to be added, because it is that much less
likely that there will be potential passengers, at any given time, within
walking distance of a given station. Trying to start a PRT system without a multitude
of destinations is like opening a grocery store that only stocks pet food,
diapers and milk and expecting it to grow from there. No selection, no customers.
I suspect we all agree, however, that PRT would prosper fabulously were it extensively
built-out to the point of having stations on every corner. That would be a “Walmart”
of destination choices! But how do we realistically get there in stages? This
has always been the fly in the ointment and is where the latest technological
trends may just come to the rescue, even if the remedies aren’t exactly what a PRT
purist would like. Let’s start with the first part of the supposition above,
walking that “short distance” to the station.
It is no secret that Uber is working on self-driving cars.
Yet as the recent fatal crash of a Tesla on autopilot points out, there will be
a lot of bumps along the way, especially in terms of liability and ethics when it
comes to driverless cars going lethal speeds. For robotaxis, it is more likely that
completely driverless vehicles will cut their teeth on the slower, short-haul
market for quite some time before attempting to navigate amongst drivers who
themselves are often driving unsafely, sometimes on foggy, icy or flooded
streets. A preferable start for an Uber would be, therefore, somewhere that would
leverage the convenience of a ride hailing app with a greater value than a
short, slower ride would ordinarily suggest. Such situations already exist in
cities with long established and heavily used transit systems, where some
neighborhoods are just out of comfortable walking distance to the nearest
station. Assigning a few robotaxis to each station would extend a transit
system’s reach. Better yet, however, would be to service a PRT station, because
that would mean that an entire trip could be arranged in a single step. In
other words, a robotaxi/PRT/robotaxi trip could be arranged by phone, giving
the full door-to-door service of a traditional taxi but with the non-stop,
flyover capability of PRT, hopefully for the lion’s share of the trip. This
would require far fewer PRT stations than the traditional grid approach, with
the PRT simply acting as a wormhole from one part of the city to another. Such
a partnership is as good for Uber as it is for PRT.
Then there is the matter of sharing the ride via Group Rapid
Transit, or GRT. Automated self-driving
technologies enable a mix of vehicles. There can be 2 seaters, 4 or 6-10
seaters or cargo vehicles all sharing the same track. A cloud-based phone app
could do more than simply synchronize the ground transportation for a PRT
passenger. It could also pair passengers with vehicles “on the fly” to create
the most efficient shared routing. Since nascent networks will necessarily have
only a few major destinations to start, it is vital to implement a business
model that can survive this stage. Such stripped-down networks tend to lend
themselves more to GRT than PRT, since it makes little sense to send large
numbers of people to the same destination in separate vehicles. Readers of this
blog will note that the concept of a multiple-tier, yet compatible track system
(Baby, Mama and Papa bear track) has been proposed herein, and GRT track is of
the “Papa Bear” variety, which supports high speeds and heavier weights, but
not steep slopes or tight turns that would be best for confined, densely developed
areas. Although not as flexible as a smaller track, it is assumed that many
important destinations are accessible by major highways anyway, and such track
would generally follow these or other uncontested routes. In a more mature
system these would form an arterial backbone for smaller, yet compatible PRT track
and station designs that are sized to more comprehensively serve neighborhoods
where space and flexibility is at a premium.
This is where cloud-based “intelligent” routing and
scheduling really makes a difference. Consider the compromise reflected in all
forms of shared, scheduled transit: Running infrequently makes for full
vehicles but discourages use of the system while running frequently promotes
system use but it may operate at a loss because the vehicles are nearly empty. With
app/cloud-based systems, however, the need can be monitored in real time and
responded to accordingly. This strongly implies an approach that incorporates
multiple vehicle sizes, something that would make sense anyway, from airplanes
to buses, if only such vehicles could be staged “at the ready,” and there was a
means to accurately predict occupancy. A paradigm of distributed, algorithmically
anticipated, haled (rather than scheduled) vehicles makes this possible for the
first time, essentially turning everything we thought we knew about mass transit
on its head.
In a fully automated, cloud-based deployment scheme, artificial
intelligence would be used in real time to choose both vehicle type and
destination to best eliminate waiting and minimize travel time while maximizing
throughput. Unlike a city bus, which often has a sign that shows
route/destination information, A GRT vehicle’s sign (and destination) might
change as it pulls into a station based on the more democratic principle of
majority rule. Perhaps such a system
could even arrange a passenger transfer to another vehicle, maybe even calling
that passenger by name and giving instructions. For that matter the vehicle
would also “know” if a passenger is making a mistake and getting off at the
wrong station. The system could even respond to passenger preferences and
histories, such as not pairing an unaccompanied woman or minor alone with a
stranger, or only pairing students of a local college with other students. Hmm…
This might give new meaning to the term “speed dating”! Seriously though, bad
experiences can be reported within a passenger app, and with cameras becoming
ever cheaper and clearer, this all bodes well for safety and passenger
satisfaction even without the watchful eye of a driver.
All of the above stands in stark contrast to the “everything
or nothing” proposition of traditional PRT, and we all know which of those two cases
has come true to date. Is PRT “dead?” Perhaps, in a way. If this is so than it
is death by a thousand cuts… a business model that is not quite compelling
because dozens of very minor (though often solvable) factors add up to a no-go,
especially in the early stages when there are too few stations to create the
“network effect.” Still, besides
creating a dizzying array of choices, our current technological prowess has
made the path towards those original goals more likely and achievable, not
less. At present it seems that GRT (rather than PRT) is probably the way to
start because the drawbacks of group travel have been largely eliminated and
GRT offers a better business model for the fewer stations that are an essential
stage in building out a network. GRT, like PRT, with a robotaxi at each end,
offers true door-to-door service, ideally with near zero wait time. It is also
notable that even with a GRT system there would be naturally be a need for
smaller vehicles. Late at night, for example, it would make little sense to use
vehicles that are sized for rush hour. This bodes well for the prospect of arterial
track sections that are eventually populated by both PRT and GRT vehicles.
Any ground-based leg of the trip, of course, will still
experience traffic delays. That, for PRT (and elevated transport in general) is
a good thing, as it will encourage expanding the aerial network into more and
more areas, and encourage players like Uber, Google, or even Ford to enter the
elevated transit business. The contrast between crawling along on the ground and
flying over the city will be like night and day, and it is hard to imagine that
they will not see the light. It is also noteworthy that future robotaxi logs
would give solid statistical evidence as to where the elevated track should
expand to next, by predicting how such a “spur” would perform monetarily,
removing the financial risk of such an expansion.
PRT does seem dead or dying as a singular, all-inclusive product/service,
in that the old model is analogous to treating
cars and roads as a single thing, when they are many: There are many types of
roads and many types of vehicles that drive on those roads and that’s a Darwinian
strength. The specific vehicle/track/operational methodologies of many past PRT
designs were often tightly integrated to compensate for technological
limitations of the day and so now require total revision in the face of the
game changing advent of autonomous vehicular control. In this new world the
track itself is the most important part to get right, because it is,
ultimately, the limiting factor. Track that is too expensive, uses too much
real estate, requires stations that are too expensive, is noisy, is affected by
weather, cannot easily be modified for various loads or spans, cannot support
high speeds, cannot be quickly and inexpensively constructed or modified, etc., won’t fulfill
its promise, or the promise of anything running on it. Above all it needs to be
flexible, and that means being designed for much more than PRT. It seems
increasingly likely that vehicles from multiple venders may be the business
model that is most likely to flourish in the ecosystem of grade separated,
automated transport, so we have to keep the track simple.
The roll of the “control system” has clearly changed. There
has always been some degree of autonomy in PRT, say to slam on the brakes to
avert a collision, for example. With newfound autonomous capabilities however,
centralized “control” becomes, more and more, merely a role of scheduling and traffic
optimization. Under such a scenario, the central computer basically makes
suggestions in real-time that are normally followed, so it is essentially the
same as central control. The difference is that the vehicles are quite capable
of working independently, just at a more cautious pace. This may seem like
splitting hairs, but it is an important distinction from a business
perspective, because it redefines what role a PRT company would have in
continuing operations by reducing an important role to a discreet, probably largely
cloud based, software layer.
What if, we might dream, a city were to say to a Google,
Tesla, Amazon or an Uber, “If we provide this track and these stations will you
design and build robotic vehicles for it? Or perhaps provide the central
traffic optimization (control) layer? While it might seem, at first glance,
that such companies would have little to gain, it is actually a pretty
interesting sandbox, as described in the previous post, and the cost of
prototyping and mass producing the actual machinery is falling every day. There
has always been a natural dichotomy in PRT between that which is naturally a city’s
business and what a PRT company can be expected to produce and perform.
Autonomous vehicles enable a “dumb” track that requires less oversight, is less
likely to become obsolete, is less tied to a specific vehicle manufacturer, and
is therefore generally less burdensome and risky to a city. This, in turn,
relieves vehicle manufacturers from a business they want no part of, that being
planners and builders of urban infrastructure. The PRT provider really becomes
more of a go-between, a builder of partnerships. Everybody’s happy!
The PRT of old seems pretty much dead... if it was ever
really alive to start with. Loosely defined, however, where we are simply
referring to smaller, haled robotic vehicles operating on a network of lightweight,
elevated tracks... well that, my friends, is alive and well. Long live PRT!