Ahh, Personal Rapid Transit: On-demand service, all trips non-stop, each user gets his or her own vehicle for the trip, just two cents worth of electricity used per mile and so on. Sounds great! So what's the problem? Why aren't there any city-size PRT systems?
One likely reason is cost: It appears that all PRT designs either demonstrated or described before now would probably cost $30-40 million per mile. By contrast, we estimate our design will cost around $10 million per mile.
A second obstacle is the understandable reluctance of cities to be first to try anything radically different. Thus we'll have to raise enough money to demonstrate the design--no small feat!
Tired of "six-lane parking lots"? We believe our design solves all the problems that have kept PRT from being used on a city-size scale. We welcome your comments!
Why
PRT is better than "mass"
Summary of operating cost
Why
it hasn't been done before
Summary of guideway cost
What's
different now
How to get it demonstrated
If so, imagine 20 percent more cars trying to use the same highways you're crawling on now-- because that's what's going to be happening in just ten years if current trends in popular cities continue (roughly two percent growth per year in the most popular cities).
Many ideas have been proposed to solve this problem: more carpooling, building HOV lanes, telecommuting, and getting more people to use public transit, among others. All these are indeed being implemented, but so far only to a relatively small extent, for reasons that have been extensively discussed by other authors. The short answer is that there doesn't seem to be any pleasant way to make carpooling significantly more attractive, or to increase the rate at which telecommuting jobs are created.
But what if there was a way to make public transit far more attractive to potential users?
Personal Rapid Transit refers to a
class of transit system having '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 offer several extremely attractive
features:
the Boeing Company built an automated transit system in Morgantown, West
Virginia that's still running today. But its vehicles were designed
to carry about 20 passengers, so under most circumstances they have to
stop at most of the stops to let them on and off.
By contrast, our much smaller vehicles will usually be carrying only one passenger--by design. As a result, they never have 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 this might seem a trivial point, but in fact it's a crucial difference--because eliminating all intermediate stops cuts the average trip time roughly in half.
To put it another way, eliminating
intermediate stops is equivalent to doubling the speed of the vehicles,
compared to a conventional, large-vehicle design.
Another successful driverless system has been installed up in lovely Vancouver, where our Canadian neighbors have built an extensive (18 miles with a 21-mile extension underway), automated transit system called Skytrain. But its vehicles are even bigger than those in the Morgantown system (each car seats 35 and cars are operated in coupled pairs), so it's still constrained to stopping at essentially every stop, and can't reasonably offer true on-demand service. Even so, Skytrain is a rousing success, and we tip our hat to our northern friends.
But imagine how much more attractive either of these systems would be if they let users go non-stop from boarding point to the selected stop! That would cut trip times roughly in half, with no increase in cruise speed or operating cost...an astonishing bargain.
So by using very small vehicles, we
cut the travel time roughly in half while providing increased comfort and
security, reducing vehicle noise and slashing the cost of providing service
during off-peak periods.
Although these benefits of using very small vehicles have been known for many years, no such systems have yet been built on a city-size scale. And it's easy to understand why: If your vehicles carry no more than two adults and two children, it takes a lot of them 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 illustrates another reason why
PRT hasn't been done yet on a city-size scale, because until fairly recently,
providing enough redundancy in a fully automated vehicle to make it safe
enough for public use was a very expensive proposition. Even
with inexpensive single-chip computers it's still a formidable task.
But low-cost computing power is only part of the solution. Until recently another crucial item was still missing: Electric motors suitable for transit use were still relatively heavy and required either brushes (a huge maintenance cost when you're operating 1,500 vehicles per loop!) or an expensive and heavy variable-frequency power supply.
Now, however, there's a new type of light-weight electric motor that doesn't use either brushes or a complex power supply. It's called a brushless DC motor, and very small versions have been used for over a decade in computer cooling fans and other small applications. But until recently this type of motor wasn't available in the higher power needed for transit applications.
That's now changed, thanks to new super-powerful permanent magnets and higher-power transistor switches. The motors we'll be using will weigh about 12 pounds apiece, and there'll be one in each of the vehicle's four wheels.
A third major difference is our guidance method. Most previous PRT designs used either some type of mechanical steering--rollers pushing against the side of the guideway, for example--or movable guideway sections. By contrast, to reduce guideway complexity and cost we decided to use a completely smooth guideway surface, and to have the vehicles follow a signal from an antenna bonded to that surface. It's a method that was patented way back in 1943 and has been widely used to guide automated trams in warehouses and similar applications. So it's been extensively proven.
(Even though this concept was patented more than 50 years ago, we've cited it as a new factor because all existing designs we know of for city-size PRT systems are either rail-based or use some type of mechanical steering.)
These three major improvements have set the stage for a design that promises to be far more reliable and much less expensive to build and operate than any previous effort in this field.
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