If you live in a major city, one of your
biggest irritants is probably traffic.
For many suburban residents the daily
drive to work takes an hour each way--with much of it spent creeping along
at 15 mph.
The emotional cost alone is huge,
not to mention the cost of the wasted time.
One of the reasons traffic is such
a problem is that the population of the top 20 U.S. cities is growing by
about two percent a year. There's nowhere near enough money to expand
highway capacity by that much each year.
Imagine 20 percent more cars
trying to use that same highway you're crawling on now-- because that's
what you'll be having to cope with in just ten years if the current growth
rate in popular U.S. cities continues.
Many ideas have been proposed to solve
the traffic problem, such as increased carpooling, building HOV lanes (which
encourage having more passengers per car), and creating more 'telecommuting'
jobs. All these are indeed being implemented. But there seems
to be a limit to how much they can help.
Another option is to try to persuade
more people to use public transit. Unfortunately existing urban mass
transit just isn't attractive to most people, especially if you already
own a late-model car. Modern cars are so comfortable--perfect climate
control, great sound systems, luxurious leather seats--that it's easy to
see why so many commuters would rather drive, even if that means an hour-long
commute at an average speed of 20 miles per hour!
But what if there was a way to make
public transit far more attractive to potential users?
Suppose a public transit system was
as comfortable and secure as a Lexus or Mercedes, and also had a vehicle
waiting whenever you were ready to go ('on-demand service'). And
suppose this system let users fly over gridlocked freeway traffic, so that
total door-to-door trip time--including end connections--was faster
than driving.
It seems likely that these features
would persuade a lot more people to use public transit.
The concept of such a transit
system has been around for many years. It's called Personal Rapid
Transit, and its distinguishing feature is the use of 'many' small, fully-automated
(driverless) vehicles running on an elevated guideway. IF such a
system could be made affordable, both in initial and operating costs--traits
that have yet to be demonstrated--it would have several extremely attractive
features:
Although there have been lots of
small-installation successes, no city-size
PRT systems have been
built. There seem to be three main reasons:
The first is initial or capital cost:
It appears that the PRT designs demonstrated or described before now would
probably cost around $30-40 million per mile--which is almost as much as
the cost of a mile of elevated expressway. If PRT can't show a significant
cost
advantage over building new expressway, it's hardly surprising that no
city politician would risk supporting an untried alternative.
By contrast, we estimate our design
will cost around $10 million per mile--less than one-fifth of the cost-per-mile
of urban expressway.
A second problem is operating cost
(including maintenance). The cost of operating and maintaining conventional
public transit systems is huge--$3 per passenger-mile isn't unusual.
Of course since PRT vehicles are driverless, our main concern is the cost
of vehicle maintenance. The small size of the vehicles means a PRT
system would have many more of them than public-transit agencies are accustomed
to, so transit operators are understandably concerned that the maintenance
cost of PRT could be prohibitive.
Later we'll discuss design features
we've incorporated to reduce maintenance time, and other factors that suggest
our maintenance costs will be much lower than with existing transit systems.
The third obstacle to PRT is that
most ground mass-transit systems are owned by some type of government entity.
Thus any innovation or change would need the support of a majority of an
area's politicians--and as noted, politicians are decidedly risk-averse.
Interestingly, a few fully automated
public transit systems have been built. However, they all
use much larger vehicles than true PRT. For example, way back
in 1973 a division of
the Boeing Company built an automated transit system in Morgantown,
West Virginia that's still running today. But because its vehicles
were designed to carry about 20 passengers (8 seated, 12 standing), during
high-demand periods they typically stop at every stop on the route.
By contrast, our much smaller vehicles
will usually be carrying only one passenger at a time--by design.
As a result,
there's never a need to make any intermediate stops.
(There's no advantage to pairing up with another passenger unless both
are going to the same stop.)
At first glance eliminating intermediate
stops might seem a trivial point, but in fact it's a huge benefit, because
it cuts the average trip time roughly in half.
Using very small vehicles (with one
person per vehicle on most trips) also increases comfort and security.
The far smaller, lighter vehicles are much quieter and less visually obtrusive
than conventional designs. Our vehicles are so light (about 400 pounds
empty) that they won't make the guideway vibrate (which shows up as noise).
This will make the system a good neighbor, which is crucial in urban settings.
(By comparison, the Morgantown vehicles have an empty weight of 8,700 pounds.)
Although these benefits of using very
small vehicles have been known for many years, and many small-scale
automated
systems using small vehicles are operating successfully, no one has yet
tried PRT on a city-size scale.
One big deterrent to developers is
that if each vehicle has a maximum capacity of no more than two adults
and two children--and most of the time will be carrying just one person--it
takes a
lot
of vehicles to provide the same hourly passenger capacity
as a conventional large-vehicle system. For example, at full capacity
our design would use over 1,500 vehicles per loop.
This requirement scared off most transit
experts because until recently, providing enough control redundancy in
a fully automated vehicle to make it "human-rated" was a very expensive
proposition. Today, with inexpensive single-chip computers, this
cost has plummeted--though it's still a formidable design task.
Why will this design will
work on a city-size scale?
It's a cliche that technology improves
with time. But unless you work in a technical field you probably
don't realize how much technology has improved in the last 20 years.
One of the biggest changes, of course,
has been the continued drop in the price of computer microchips, even as
those chips have gotten faster and far more powerful.
In 1986 the fastest personal computer
ran at 8 MHz and had enough memory to hold about 128,000 characters or
numbers ("128 KB"). Its only storage was a "floppy disk" that could
hold 720 KB of data. Today a 'plain vanilla' PC runs at 2000 MHz,
comes with at least 256,000 KB of memory and a hard drive that can hold
100,000,000 KB of data. In other words, a garden-variety PC today
is 300 times faster, has 2000 times more memory and 100,000 times more
storage space than its ancestor of 20 years ago.
Even more amazing is that the 1986
model sold for $1,200 in 1986 dollars-- equivalent to around $2,800 today.
And that didn't include a monitor! Today our 'plain vanilla' PC--with
color monitor and printer--sells for about $350. In effect, you now
get 1000 times more power than 20 years ago, for one-eighth the price.
Power-per-dollar is just one improvement:
Another is shrinking size. Manufacturers are now putting a computer
ten times faster than a 1986 desktop on a single chip.
Costing less than ten bucks.
The availability of fast, reliable
single-chip computers will make it possible to produce a triple-redundant,
self-diagnosing control system for our vehicles for less than $500 apiece--about
one percent of what it would have cost just ten years ago.
So inexpensive computer power is a
huge enabling factor. But there's also another crucial item that
wasn't available until recently: The electric motors used in conventional
transit applications (subways and trolleys) use carbon 'brushes' to get
electricity into the rotating core of the motor. In a popular PRT
system these brushes would wear out in a year or so. In a city-size
system with thousands of vehicles, replacing worn brushes would be a huge
maintenance cost.
For an economically-viable, city-size
PRT system we needed a brushless motor with lots of torque. A type
called a brushless DC motor looked promising, but until just three years
ago this type of motor had only enough power to run the cooling fan in
your computer.
Now, thanks to tremendous improvements
in permanent-magnet and power-transistor technology, these motors are powerful
enough to move our small vehicles. As with the computer chips, the
result is simply astonishing: the motors we'll be using are about the size
of a large coffee cup, weigh about 20 pounds apiece and are able to deliver
20 horsepower for short bursts if needed.
To get an idea of how big an improvement
this is, if your car's engine could be improved that much it would measure
just 18 inches on a side and would weigh one-third as much as the gasoline
engine that powers your car now.
While our design has many innovative
features, a city-size PRT system wouldn't be feasible without these two
improvements by other parties--faster, less-expensive electronics and a
light, powerful, brushless electric motor.
With them, we believe it's possible
to revolutionize urban transportation--and by doing so, to significantly
improve the quality of life in major cities.
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section: The guideway
guideway, they obviously wouldn't be affected by expressway traffic jams--one
of the most attractive benefits;