Let’s start with a bit more about
minimal systems. In my recent post, “For
Example,” I experimented with the limits of capacity within the confines of a
minimum of track (4 miles) and (4) stations. The
reason such exploration is necessary is because for PRT to be adopted by a city
as a viable mode of transportation, it must first pass the litmus test of being
the cheapest solution to an immediate problem. Bureaucracies aren’t known for being far-sighted
or visionary, and individual decision makers need to cover their butts every
step of the way. They are, after all,
custodians of taxpayer money. Therefore the fact that PRT should be set up as a
distributed system with many small stations really doesn’t matter. To these people, at this stage, any small
station is one that should be eliminated to save a few bucks. Their mindset is essentially reactionary - “If
it ain’t broke, don’t fix it!” Widening
roads is their first instinct, not making a pedestrian-friendly city. The exercise in “For Example” imagined stations
with mythic levels of pedestrian traffic, just to examine the logistics. What is not so imaginary, though, is that only
moving great numbers of people will get the attention or funding that a project
needs to get off the ground. ULTra’s
Amritsar project, I think, is case in point. With up to 100,000 visitors per day and only 7
huge stations, it is not at all what most PRT pioneers envisioned. Yet that was what got enough traction in the
real world to actually get funding.
Even without the timid bureaucracy,
there is a basic problem with a small, starter PRT network - there are liable
to be too few destinations available to attract a steady stream of walk-up
customers to any given station. Or put
the opposite way, there are too few stations feeding any given destination. Either way you look at it, it is the network
effect in reverse. It’s the internet
with only a dozen web sites. In addition
there is a matter of distance. For track
to pay for itself it needs to be used. If
the stations are far apart, there will need to be more vehicles on route to pay
those bills. In the “For Example” post
there were vehicles leaving four stations at one per two seconds at each
station to keep the track at full capacity. Suppose we had twenty stations over a similar
four mile loop. That is still one
vehicle leaving each station every ten seconds if you expect to have the track
at full capacity. Now where can you find that kind of pedestrian density for
all twenty stations? Luckily, with
proper engineering, both track and stations can be made cheap enough to break
even at far less than full capacity, and vehicles ought to be mainly amortized
by mileage, so there is still hope. But
the problem of small networks is still real, nevertheless.
So PRT badly needs a strategy to
“get a foot in the door” so at least one network can grow to reach critical
mass. Otherwise it is very hard to see
how this “chicken or the egg” dilemma can be broken. Trying to ensure that every possible situational
roadblock has been addressed, I have designed ultra-small open-air stations,
ultra-high capacity stations, track that can turn any corner, vehicles that can
even drop down vertically … you name it. But the best strategy is to have some kind of
a way for a transit authority to ease into PRT - to “dip their toes in,” so to
speak. This must involve some kind of modest starter network that doubles as
being clearly the best, most cost effective way to solve some big, immediate mobility
problem.
One very insightful reader
commented that a good place for PRT to start might be a city (or cities)
straddling rivers or other bodies of water. I must say that this is the best suggestion
that I have heard in quite some time. Let’s examine it.
In such cases a good percentage
of the mobility problems might be for lack of bridges or good approaches to
them. Bridges, like roads in general,
must be engineered to handle bumper-to-bumper cement trucks, so they are vastly
more sturdy and expensive than they need to be to accommodate a steady stream
of puny humans in evenly spaced, featherweight pods. A bridge for PRT vehicles would be absolutely
tiny - in both stature and cost - even while being capable of delivering people
at a prodigious rate. But the bridge itself
is just the beginning. On either side of
the bridge there must be approaches to it.
These days to justify a new
bridge, you pretty much need to be building it as part of a freeway. When is the last time you saw a city inaugurate
a brand new two lane bridge? Consider the
devastating effect that steering that much traffic towards a new crossing point
would do to the riverfront real estate on each side. Also, it’s not just on the banks. Unless there are already riverfront highways
on both sides, such roads will cut neighborhoods in half, bring noise, and, of
course, will be terribly expensive and disruptive to build.
Adding a PRT bridge would
require no new roads, no demolition. Transit
planners would have a totally unique opportunity to create a painless shortcut between
the most important destinations on each side. Also, cities often make riverfront property
into parks because of the possibility of flooding. In many cases these are
important tourist destinations, with nearby businesses catering to pedestrians as
well as drive-up customers. Joining such
car-optional areas on either side of a river would be a boon for such destinations.
Car-free zones are highly symbiotic with
PRT, since every additional loop extends that “cars not required” status further.
Add a zoo, theaters, museums or a
shopping mall, and the system gets real gravity. A group of destinations
becomes the destination itself, once it is all walkable. And let’s not forget,
apartments and condos on “The Riverwalk” would then follow, and those folks
could live quite well without a car. Real estate developers love this kind of
stuff. One deal leads to another as the whole area goes “upscale.”
One twist I would like to mention
in passing is the possibility of using old bridges. I recently heard of a case in Louisville,
Kentucky where they saved the old “Big Four” railroad bridge across the Ohio
River, and converted it to pedestrian use. This reminds me of the “Rails to
Trails” movement, where they convert unused railroad lines to “hike & bike”
trails. I’ve often wondered if they would consider sharing their trails (bridges
and all) with a nice, quiet and green PRT system!
Anyway, in a nutshell, the premise
is this; Building a shortcut between important destinations
on either side of a body of water may be too expensive and disruptive to
contemplate for ordinary road or rail. PRT, however, being lightweight and elevated,
can make the overland portion with the least disruption, and requires a bridge
costing only a fraction as much. To top
it off, bodies of water typically have parks along their banks that could use
PRT service as well. These factors might
combine to create the potential for an inexpensive starter PRT system that can
still attract sufficient ridership to turn a profit.
Could this be the “foot in the
door” that we’ve been looking for? It certainly seems to me that PRT developers
would do themselves a big favor by having the resources in place to accomplish such
a project.
