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Personal Rapid Transit
Transit YOUR way: ready-to-go, private, dependable, point-to-point.
Although the following introduction is good, you'll find the "world's best general-knowledge PRT website" (ATRA 2004) at http://kinetic.seattle.wa.us/prt.html
To learn more about PRT developments in the San Francisco Bay Area, visit http://www.electric-bikes.com/prt-info.html
Personal Rapid Transit (PRT) is a revolutionary transit technology that promises service that's flexible, prompt and dependable. It also requires less money, environmental impact and time to construct. Simply put, it offers the best transit value available.
PRT only became practical within the past 10 years due to advances in microprocessors, sensors, telecommunications and software. Instead of using large metal containers to move many people (e.g. a bus or BART train), PRT uses small plastic (i.e. fiberglass) vehicles or "cabs" to move a few people - or a person and their baggage. Think "two-seater sports car", like a Miata. Cut off the back (trunk space) and the front (heavy and complicated engine and drive train). Then elevate that "cab" onto a guideway so you ride above all the other traffic.
Stations, or "ports", are like bus stops located at ground level (or elevated and accessible by elevator). Most times a PRT cab will be awaiting you at your local port. Select your destination and get in. Quickly and quietly your cab leaves the station and rises up to merge with other cab traffic on the main guideway. Since all ports are offline, you never have to stop until you get to your destination port. There, your cab automatically leaves the main guideway and drops down to ground level for you to exit. Your cab is now available for someone else. Uninterrupted flow is the key to system capacity, not vehicle size. So a PRT system can carry as many people as multiple lanes of freeway traffic.
Financially, PRT compares favorably with light rail (LRT), electrified rail, subways, and our local San Francisco Bay Area BART. PRT offers comparable (or better) service for 1/10 the cost of BART - or 10 times the service for the same price. Environmentally, PRT also excels. Using proven technology, PRT systems can be easily built as demand grows. This means less up-front investment. PRT also better matches the needs of suburban sprawl.
When you compare benefits and value between transit systems, you'll find that PRT can't be beat for most transit needs. Here are the four leading PRT initiatives:
SkyTran - www.skytran.net
- SkyWeb Express - www.skywebexpress.com
- Urban Light Transport (ULTra) - www.atsltd.co.uk
- MegaRail - www.megarail.com
- MISTER (Metropolitan Individual System of Transportation on an Elevated Rail) - http://www.mist-er.com/index-en.htm
. . . .
Link to Further Information and Status of PRT Projects.
www.electric-bikes.com/prt-info.htmlSunnyhills Neighborhood Association's proposal for a city-wide PRT system would save transportation dollars. Help this Milpitas organization demonstrate public support -- sign a resolution.
Learn more about PRT's potential for Milpitas at
www.electric-bikes.com/prt-milp.htmlPalo Alto-based Cities21 and the Advanced Transit Association built a full-size, portable mock-up of a PRT guideway and cab which can be transported and exhibited to the public. Visually demonstrating that PRT blends with our Bay Area cities moves us closer to solving many transportation problems. Learn more about the project and make tax-deductible contributions at this site:
http://www.advancedtransit.org/PRTmodelLearn more about PRT's potential for Santa Clara County at
www.electric-bikes.com/prt/bart.html
www.electric-bikes.com/prt/bart.htmlCitizens for PRT is working with the public and private sectors to develop a test-case PRT in the Bay Area. Keep up-to-date by subscribing to PRT-Info for announcements about new developments in PRT science or public acceptance.
Cabs
Cabs carry 2 - 4 people, or people plus baggage, or cargo. Maximum passenger/cargo weight is 500 - 750 lbs. Some cab designs allow handicapped and cyclist use. Other systems require multiple cab designs to accomodate these "non-standard" users. BACK to introduction.
Guideways
Guideways holding up light cabs can also be small and lightweight. About the size of a paired set of escalators, the guideway is compatible with a wide range of urban and "edge city" environments. Support posts, which require a footprint of less than four square feet, are spaced 50 - 60 feet apart. BACK to introduction.
Ports (Stations)
Ports, small stations where people board and leave cabs, fit in. About the size of a bus stop, ports can be sited at ground level, elevated, adjacent to buildings, or even within buildings. The left two images show minimalist elevated ports. Seat are positioned at standard chair height above the platform.
Even with the guideway above the port (second image), the scale is still small enough to blend into populated areas. Remember, that a small guideway can carry the equivalent of two freeway lanes of traffic. PRT blends in like no other transit system.
The third image draws a picture of a handicap-accessible cab with pay point. Cabs designed and built for different purposes (handicapped, cyclist and bike, cargo) allow for a simplified version of the standard cab. Specialty cab passengers can expect to wait no more than 5 minutes after they call for a cab.
The fourth image presents a fully enclosed station for harsh weather areas.
BACK to introduction.Construction
. . .
PRT construction is far less disruptive than putting in new sewers or resurfacing the streets. Again, light is the key concept. Guideway construction is easy compared to LRT or BART because the parts are smaller and lighter. A hole is dug for the supporting pole. The pole is inserted. The track is laid across the top and a wiring crew hooks up the power. Installation is straight forward with minimum disruption to normal activity in the area. The support posts and 60-ft. guideway sections install easily. Modular manufacturing makes guideway components both inexpensive and simple to interconnect. This leads to a system that is affordable to modify/expand/re-use as needed.
Ports (stations) can be tiny, modular and easily sited almost anywhere! Minimal land requirements for ports and guideway supports reduce conflicts with existing infrastructure: underground utilities (water, sewer, storm drains, gas, electric, cable TV, telephone, fiber optic cables), trees, private property rights, sidewalks, etc.
Here's the bad news from Charl du Toit <charl@ihug.co.nz>:
Foundation engineering is an inexact science because nature does not play according to nice uniform rules. On the same street there will be half a dozen different soil conditions. The worst will be found right where you need to put the footing of a load-bearing pylon. One of the reasons for this is that everybody who has built around the place before, has avoided the spot because it's too difficult to build on.
Generally foundation engineers are hugely conservative because no one thanks them for cutting 0.1 cubic meter of concrete out of a footing if there is a chance the building cracks as a result. A mass-produced system such as you envisage would have to cater for the lowest common denominator along the route as well - you would hardly do an individual design for each support pole. So unfortunately you end up with a bigger and more expensive solution than you really need.
In the urban environment as you point out there is the complication of underground services. These are always where you don't want them, and never where the utility company says they should be. There is no way around the problem - literally. You would have to find and identify services all along the route. This is not trivial; a road widening project I was involved with used 35% of the total budget for services relocation. In your scenario this cost could easily exceed the foundation costs.
Here's what you would do:
1. Choose single-pole footings, better in the urban environment because you have less chance of hitting a service.
2. Along the route, you would go along to all the utility companies, and regional services authorities, and the local municipal authority, and get service plans.
3. Get a service detection specialist to physically walk the line, marking services encountered. They use several methods of detection, including metal detectors and subsurface radar. The more sophisticated the method, the more they charge.
4. Dig trial pits at each pylon to locate services. It's better to break the service at this point and have time to plan a fix, ahead of your main construction. I have tried an innovative waterjet-powered method which is non-destructive and seems more promising than the digger bucket method of finding stuff underground.
5. Report back to the service owner on what you have found. Then eat up whatever preposterous demands they make regarding protection of their service (never mind that it is in the wrong place). Often they will not permit any structure to built over them, and the service will have to be moved. Generally the utility operator will not permit you to touch the service, and will charge you whatever they feel like to do it on your behalf. They also do not operate on the same timescale as you do. If it is not possible to move the service, you have to design a costly structure to bridge it, including allowance for future access to it.
6. Cities require building permits for this kind of structure, so you would have to present the final design for approval. This generally would be subject to public consultation. If you thought the utilities were bad, try addressing a public meeting consisting solely of those who are there to stop you building something in front of their bedroom window. When you've changed the design to suit everybody you will know for the first time what your final guideway cost is likely to be.
Economics
PRT is affordable in four ways:
Affordable to build/construct.
- Affordable to operate and maintain.
- Affordable to the consumer/user/rider.
- Affordable to modify/expand/re-use as needed.
Cost to build PRT systems will run about $10M/mile. That includes elevated guideways, enough cabs to saturate the area, and all control systems. Three independent organizations have come to the same rough figure. Even if PRT costs twice that, it's a deal compared with other forms of transportation:
New LRT routes in Santa Clara Valley will cost $65M/mile.
- BART from Fremont to San Jose will cost $175M/mile.
- Sunol grade HOV (car pool) lane on southbound I-680 between Hwy. 92 and Hwy. 237 (Calaveras Boulevard) costs $84.4M for 13 miles ($6M/mile); the complementary northbound HOV lane will cost $127.3M ($10M/mile). That's a total of $16M/mile for both directions, excluding land costs.
- I-880 widening (from 4 to 6 lanes) between Montague Expressway and 101 is costing $60M or $24M/mile ($60M/2.5 miles) for both directions, excluding land costs.
- The SJIA Automated People Mover (APM) is estimated to cost $70M/mile without land acquisition. (The ULTra folks estimate they could provide twice the mileage - including a connection to the CalTrain station - for half the cost.)
- The cost of conventional rail runs $20 to $40 million per mile.
One key to PRT's low price tag is costs avoided. Easily routed guideways can share right-of-way with public roads and avoid costly property acquisition. Unlike small, easily sited PRT stations, station size (and cost) of rapid rail systems are fixed at the maximum-length train (10 cars = 700 feet for BART stations). Another big cost factor are environmental mitigations identified in the transportation project's Environmental Impact Report (EIR). Being elevated with small widely spaced footings, PRT's environmental impact and required mitigation is small compared with other transit systems. Those small footings also mean fewer and smaller utility line relocations. Finally, due to minimum disruption of existing traffic patterns, much less is spent on traffic control and detours.
Operations and Maintenance (O&M)
Even after construction, PRT is cheap to operate compared with other transit. Here are estimated operation and maintenance (O&M) costs per passenger mile:
PRT = $0.15, commuter rail = $0.28, LRT street cars = $0.45, buses = $0.55PRT O&M is expected to cost 1/3 as much as Santa Clara County's bus/LRT system. Here's an illustrative example: A prime item in the O&M budget is energy costs - both monetary and environmental (global warming). Due to frequent stops and starts, about two thirds of the operating energy used by today's transit vehicles in an urban area is kinetic energy lost in heat as the vehicle is braked to a stop. Therefore, elimination of the intermediate stops by itself almost triples energy efficiency.
See the paper "Optimization of Transit System Characteristics" (listed on Publications page at www.taxi2000.com) for fundamental reasons why the PRT concept will yield the lowest cost per passenger-mile of any transit system.
Partly due to lower O&M costs, PRT fares are expected to completely pay for O&M. Fares on other transit systems come nowhere near paying for O&M. For example, of its total operating costs during 2000, Santa Clara County's VTA recovered only 16.3% from fares ($15.546M from fares / $95.232M operating expenses). The rest is subsidized - leaving fewer dollars for other needs.
Some experts estimate that PRT fare recovery can also pay for system expansion. Once a PRT system reaches a critical size, it generates enough profit to finance it's own growth. That critical size is surprisingly small. In dense, high-traffic areas a mere 30 cabs running on 15 miles of guideway is expected to generate positive revenue (http://www.skyloop.org/financial/sl-financial-plan.htm).
Transit pricing is invariably subsidized to keep user fares affordable. Comparing the size of subsidy per passenger mile is one way to judge the cost-effectiveness of a transit system. PRT's promise to cover O&M from fares alone, without subsidies, separates it from other transit systems.
Giving PRT the same subsidy per passenger mile as other transit systems creates two obvious opportunities:
providing service for free
- financing further PRT growth (and usefulness)
Modify, Expand or Re-use as Needed
Rail-based transit systems, being inflexible, adapt poorly to changes over time. PRT is flexible and can be modified, expanded, or even moved, as needed. A light-weight, modular PRT guideway is easily modified to add or delete ports and routes. Adding loops or even networks to the original system is relatively easy. Even deconstructing a PRT system (or portion) for re-use elsewhere makes economic sense.
Point-to-Point Transport
Point-to-point transport offers three big advantages over transit which stops at stations along the way:
People arrive at their destinations much quicker. Point-to-point transport effectively doubles the average speed of transit. For example, although BART can travel at speeds of 90 mph, it actually averages 40-45 mph along its route due to all the required stops. PRT's running at only 45 mph can match the speed of BART. However, speeds up to 100 mph are achievable with current technology. Even at 70 mph, a PRT passenger will arrive at his destination in about half the time of driving his/her own car.
- Less energy is consumed. All those starts and stops take energy. Saving energy saves money and pollution. If we are to meet our Kyoto agreements on reducing CO2 emissions, we must address our wasteful transportation systems. Until enough riders board a bus or LRT, it is less energy-efficient than single-occupant automobiles.
- Passengers can freely engage in other activities. There's no concern about missing their port, so they'll be free to fully attend to whatever else they'd like to do - even sleep.
System Capacity or Volume
Can small cabs move large numbers of people like traditional mass transit? Yes. Uninterrupted flow is the key to capacity, not vehicle size. For example, 60-passenger buses arriving two minutes apart (a very high flow rate for an American bus system) can carry 1800 passengers per hour. PRT vehicles coming every two seconds can provide the same capacity. PRT capactiy depends on headways:
0.5 second = 120/min or 72000hr
- 0.6 second = 100/min or 6000/hr
- 2.0 seconds = 30/min or 1800/hr
A commonly accepted safety zone on roadways is 2 seconds between cars. Although automatic control of PRT cabs is safer and more reliable than human drivers, let's assume our PRT systems starts with that comfortable two seconds of space between each cab, aka "headway". At that headway, 1800 cabs per hour can roll down the guideway. That's 1800 people per hour assuming sole-ridership will prevail (30 cabs/min * 60 mins/hour = 1800 cabs per hour). That approximates the maximum volume of a freeway lane of traffic (2200). After a few years of operation, we may have the confidence to reduce the headway times to only one half second. That would quadruple throughput to 7200 cabs/hour. Now we're talking the volume of three freeway lanes in less than the space of one physical lane.
Now, compare that volume to LRT and trains. Although LRT systems may be designed for high volume, the actual limit of any operating LRT system in the U.S. is 1200 riders per hour; peak in Sacramento is about 1000 passengers/hr. Likewise for trains where the theoretical limit is 20,000 riders/hour, actual loading often tops out near 7000 riders/hour. An exception may be BART where reports indicate near-saturation of the trans-Bay tube at 20,000 riders/hour [is that one way, or both?].
Another capacity comparison could be made with computer controlled cars as demonstrated near San Bernadino, CA. Partners for Advanced Transit and Highways (PATH) ran Buick Le Sabres by computers on a dedicated strip of freeway with magnets embedded so the cars could be computer controlled. They ran for thousands of miles at 60 mph with 0.25 sec. headways. Some of PATH's research, particularly its work in the Advanced Vehicle Control Systems area, has been covered by a range of media. http://www.path.berkeley.edu/PATH/Publications/Media/
Speed is another factor in capacity. Here are critical ideas from PRT pioneer Ed Anderson:
Subj: RE: [prt-talk] Digest Number 56
Date: 5/27/01 5:32:19 PM Pacific Daylight Time
From: jeanderson@taxi2000.com (Ed Anderson)You mentioned some of the system problems. Tires vs. maglev are not the most important considerations. Curve radii increase as the square of the speed and off-line guideway lengths increase in proportion to speed. These are the most important factors. Life-cycle-cost per passenger-mile is the annualized capital + operating cost divided by the annual ridership. Costs increase with speed regardless of the means of suspension and ridership will increase with speed to a point. After a certain speed, costs increase faster than ridership so the cost per passenger-mile increases. - JEA
So, pick a speed that ensures high ridership by offering 1) a low cost per passenger-mile and 2) speeds that compete with the automobile . Absent any analysis, I pick 40 mph. Let's start engineering with that operating speed in mind.
Here's some capacity numbers from the bike folks: It takes three lanes of a given size to move 40,000 people across a bridge in one hour using automated trains, four to move them on buses, twelve to move them in their cars, and only two lanes for them to pedal across on bicycles.
A vehicle at a red light requires about 240 square feet of space (that's a standard 12-foot lane with a standard 20-foot long "envelope" per car). At 20 mph, it requires about 700 square feet. And for a car zooming at 40 mph, the number balloons to about 2,000 square feet. Maximal traffic on a highway lane runs at 2.2-second intervals. At 10 mph that is 1000/hr; at 30 mph about 1500/hr. It never gets more about 1500/hr because the vehicle grows with velocity. At 50 mph, a car is 1,285 feet long. PRT capacity or speed does not decrease with a heavy load; at 2 second headway, it will have 3 times the capacity as a landeof traffic, and at 0.5 second headway, it will have 12 times the capacity.
Proven Technology
Most hardware components of PRT systems are "off-the-shelf" technology. For example, most robotic-operation components have been proven in Automated People Movers (APM) around the world. The current count of 114 active APM systems is distributed about equally between:
Airports
- Leisure (zoos, casinos)
- Institutional
- Transit
Another part of PRT's robotic operation depends upon Adaptive Speed Control (ASC), a feature available on the new S Class Mercedes. Forward-pointing radar senses all obstacles or vehicles in the immediate forward path. Whenever a Mercedes is on "Cruise Control" and senses a slower vehicle ahead, it slows down and matches that lower speed. Automatically, the Mercedes stays a safe distance behind. Likewise, in the case of slow or stopped PRT cabs ahead, your cab will automatically slow down to match that speed.
Other component technologies that you're seen elsewhere: telecommunications (cell phones), security cameras (retail stores), microprocessors, sensors, linear induction motors.
Control systems are the one unproven area. Although software simulations have verified the basic operating principles, exhaustive testing of an operational PRT system is needed. However, given routing algorithms developed for the Internet and robot-controlled factories, this challenge is surmountable. BACK to introduction.
Common Concerns
This section will be fleshed out as we move along and hear concerns repeatedly. Please send your suggestions and concerns to rob.means@electric-bikes.com
Examples:
"I think it's an altruistic solution that won't work. Like the idea of public bicycles that people can just pick up and drop off as needed, American nature will not permit it to succeed. People are too wrapped up in possessions and not inclined to sharing. It will look ugly up there where it's in plain view."
"Being elevated, PRT passengers can see into nearby residences. Understandable NIMBYism from residents along proposed routes will prevent construction."
Can PRT handle peak volumes like when a train arrives or a stadium game ends?
Considers this demand scenario: a Friday evening 'peak hour' before the start of a Cincinnati Reds baseball game at Cinergy Field. During this hour 5338 passengers enter the various PRT passenger stations, of which 88% are going to the Cinergy Field stations and the balance to other stations in the network. When allowed to run to its completion the simulation produces these resultant statistics, including an Average Wait Time of less than one minute and a Maximum Wait time of under five minutes. See the detailed network simulation at http://www.skyloop.org/sims-video.htmWill the visual impact of PRT be acceptable? Visual impact is important in all transit systems. Many rail transit systems are placed underground because a ground-level system requires destruction of too much existing property and an elevated system is too massive and noisy. A PRT guideway has less than five percent of the cross sectional area of a rapid rail system, will generate almost no noise, and has an external appearance that can be varied to suit any specific community. For a series of representative photos, see http://advancedtransit.org/-visual.htm
Visual impact of an APM system (which is physically larger than PRT) is less than an at-grade LRT system with it's overhead catenary. which are being approved across the country. Note also that the Miami, Detroit, and Jacksonville people-mover (GRT) systems have guideways far larger than Taxi2000. Yet, they were approved in downtown areas with little complaint about visual eyesore.What about safety? Although safety will be engineered into the system, realize that PRT engineers OUT the biggest liability - human error. Ninety percent of all accidents - whether in cars, trains, or planes - is due to operator error.
What if a cab breaks down on the guideway? Taxi2000's strategy for this type of failure goes like this: If a vehicle stops on the guideway and can't move under its own power, the vehicle behind it soft engages and pushes the vehicle into the next station. To do so each vehicle is equipped with a special push-mode coupler that permits it to attach to the vehicle ahead, release the parking brake and operate the switch. When the vehicles arrive at the station, the passengers are asked to disembark and reorder their trips on following vehicles with some kind of compensation for their inconvenience. The pushing vehicle then pushes the failed vehicle out of the station to the nearest maintenance facility, and thus the station is cleared. Such an operation will be under the close supervision of trained personnel, who function from a control room. It is important to estimate the probable mean time for such an incident. Based on various studies of redundant computer-controlled cabs, the result could be stated in the following way: In a fleet of 1000 vehicles, the mean time between pushing incidents would be about 300 years. If one computer produces an error, control is shifted to the good one and the vehicle is permitted to finish its trip and then proceed to the maintenance shop, where the failed unit is replaced. The mean time between such incidents is calculated in the paper "The Effect of Redundancy on Failure Frequency in PRT," which can be found on www.taxi2000.com.
PRT is a humanizing technology. The new system requires vehicles to wait for people rather than people to wait for vehicles. It provides a short, predictable, nonstop trip on a network of guideways, possibly inside to inside, a seat for everyone, climate control, no transfers, minimum or no wait, 24-hour on-demand service, ease of use, privacy, no crowding, space for luggage, no jerky motion, no objectionable sounds, no smelly fumes, minimum anxiety, maximum safety, minimum land use, and minimum disruption so that businesses need not be closed while the system is installed.
Other concerns are probably covered in the "38 FAQs" section at www.taxi2000.com. Further information is at http://www.skyloop.com/resources.htm
Environmentally Easy
That's easy on the earth - and easy to understand. Transport by PRT instead of automobile is estimated to reduce both energy use and harmful emissions by a factor of 10! (Surprisingly, LRT uses more energy per passenger than automobiles.) Even compared to relatively clean and efficient BART, ULTra's 2Kwatt per cab consumption of electricity is small. Such dramatic reductions in energy use result from the combination of an electric drive system with light weight, aerodynamic cabs. (For a deeper discussion of the factors affecting efficiency, see the Skeeter recumbent electric bike.)
In addition to reducing energy use and pollution, increasing resource productivity is key. PRT uses fewer resources and produces more results from them. Small, light-weight infrastructure is the most obvious example. However, due to small size and high occupancy rate (i.e. efficient re-use) of cabs, the material requirements for vehicles is also much less than other transit systems. In short, PRT exemplifies the Principles of Natural Capitalism.
A point of fundamental importance is that PRT ridership studies show that PRT will be able to attract typically 20 to 50% of the trips in an urban area, whereas LRT attracts less than 3%. The environmental advantage of PRT will therefore be enormous.
There is an enormous difference between a PRT system and an auto system:
Land Use: 1% vs. 30%-70%
Accidents: < Auto/1,000,000
Energy Use: Auto/4
Air Pollution: None
Driver's License: None needed
Therefore, replacing use makes a big environmental difference. Add in that PRT ridership studies show that PRT will be able to attract typically 20 to 50% of the trips in an urban area, whereas LRT attracts less than 3%. The environmental advantage of PRT will therefore be enormous.Revolutionary Transit Technology
Using PRT is similar to taking the bus or train. Only a slight change is required of people. However, in terms of societal impact, PRT may prove to be more than just a new transportation technology. It may prove revolutionary. It promises a change in transportation as great as the leap from canals to railroads, or from railroads to automobiles.
To examine the history of transportation over the past 250 years is to see the rise of three major technologies. First, canal transportation developed after 1750. Railroads flourished after 1825 and then automobiles had their turn starting early last century. Each transportation system required entirely new infrastructure and vehicles. Also,each new transportation system brought benefits far out-weighing any available by simply applying new technology to the old transportation system. "So what if your canal barge has a computer control; you still can't find a place to park it."
Put in the context of 250 years of transportation history, PRT could be the next revolution in transportation. BACK to introduction.
Transportation Needs of Suburban Sprawl
Railroads served well the needs of the nineteenth century with its big cities and small towns strung out radially from the city along the tracks. That big city/radial arm pattern doesn't match with today's suburban sprawl. Because of that mismatch, corridor-type transit systems (electrified rail, LRT, commuter rail, and buses) don't serve us well any longer. That's one reason only 3% of the US population uses them.
Today, we "edge city" residents want to get from everywhere to everywhere. So, something like a grid transit system overlaying our sprawl is needed. PRT offers the two features required to create such a system:
being elevated, it can overlay the existing sprawl without major disruption
- consisting of loops, it can expand and flex as needed into shapes that serve our sprawl
An example of that flexibility could lie in substituting PRT for Pedestrian Over Crossings (POC). POCs enable pedestrians and cyclists to cross over railroad tracks and freeways. They cost upwards of $1.25M each. Installing a short single-loop PRT with two stations may be cheaper and easier. For example, ULTra's passive guideway is estimated to cost $1.8M/mile. After paying the $360K for the 0.2 miles of guideway - plus funding cabs and control system - the budget for a PRT crossing would still be well under $1.25M.
Excellent engineering solutions elegantly solve a problem AND contribute to solving other problems as well. So it is with PRT. Not only does it provide a high-service, low-cost transit system that quadruples ridership with each doubling of its size, it supports other existing forms of transit. For example, the proposed Cities 21 feeder system could increase ridership on both CalTrain and buses in its operating area. BACK to introduction.
Usefulness/Value
One way to evaluate complex projects, like transit systems, is to rank and value their benefits. Value represents the importance of the benefit (1=low, 5=high). For example, "affordability" gets a high value rating, either "4" or "5". Ranking shows how well the transit system provides that value. Ranking also runs from 1(low) to 5(high). BART, for example, gets a low ranking of "1" because it's so expensive.
Another important benefit is "continuous flow", that is, going from A to Z without a lot of stops in between. That's important because, without a lot of stops, you get to your destination sooner while also saving energy. Such transit systems allow passengers to read or work without dividing their attention to watch for their destination. So, for the benefit called "continuous flow" (value = "4"), PRT gets a top ranking of "5" which earns it a rating of 20 points in this category (4 x 5 = 20).
In the table below, the numbers are a first guess. Community input will be required before confidently assigning values. Transit types include "train", which is standard heavy rail, and "e-train" which is electrified rail. Bracketed numbers (e.g. [1]) refer to notes below.
Benefits
value
PRT
bus
LRT
BART
train
e-train
affordable to implement/build
4
5
4
2
1
3
3
continuous flow
4
5
2
3
4
4
4
expandable (both track and vehicles)
3
5
4
3
2
3
3
low operating costs
4
4
3
3
2
3
3
supports local industries
2
4[1]
2
2
2
2
2
environmentally benign (resource usage, energy consumption, air pollution, noise pollution, visual pollution, wildlife impacts)
5
4
3
3
2
3
3
convivial (feels good, comfortable, ergonomic, safe/secure, stress reducing, private space)
3
5
3
3
4
3
4
ready-to-go-ness/availability/headway
3
5
2
2
3
2
2
throughput/# of people per hour
3
4
4[3]
3
4
4[3]
5[3]
uses modern technology
2
5
2
2
3
1
2
post-quake alternate to primary system (auto traffic)
1
4
1
3
5
5
5
speed of construction/implementation
5
3
4
4
1
4
4
ease of financing
5
4[2]
4
3
2
3
3
ease of political implementation
5
1
4
3
3
3
4
Total Value
195
157
141
122
150
163
PRT
bus
LRT
BART
train
e-train
[1] PRT uses lots of integrated circuits (chips) for communications, control, sensors, etc.
[2] The downside of being early adopters of PRT is that financiers may be hesitant. However, unusual sources are possible: Great Mall, SVMG, foundations, private individuals ("When you buy a cab, we guarantee you'll get the next available cab at your port.").
[3] various ratings changed in response to this e-mail:
Subj: BART stuff
Date: 6/6/01 11:18:38 PM Pacific Daylight Time
From: okuzumi@silcon.com (Margaret Okuzumi)
To: rob.means@electric-bikes.com (rob.means@electric-bikes.com)
I had a quick comment on your "comparison chart". No way should BART get a 4 for throughput of people per hour. The single level cars have much less capacity than ACE or Caltrain's two-level cars. That's why there are so many standees on BART. The scores for train or e-train should be higher than BART's, especially since they can also be run at high frequency. Buses should get a score at least as high as BART. Running buses every 30 seconds, you can get pretty good throughput. Grand Central Station/NY has buses leaving every ten seconds during the rush hour. - MargaretFor another cost/benefit chart comparing PRT, car, bus and LRT, click here.
Confusion between PRT and GRT often occurs. Although the two technologies share certain characteristics (automated 24/7 service and off-line stations), they are distinguishable by the number of passengers each vehicle carries. PRT cabs carry 1-4 people, while GRT vehicles carry 10-30 people.
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R&D leaders in this area include CyberTran (left) and AusTrans (right).
Austrans is an automated people mover system. The system uses driverless, air-conditioned vehicles, the size of mini-vans, operating on narrow gauge rails on dedicated guide-ways – installed either above, on or below ground levels. These lightweight, electrically powered vehicles are low in energy demand and provide a service that has minimal impact on the urban environment. A Sydney-based test track includes several features to demonstrate and validate the performance specification for Austrans. Features such as an 8.0 metre turning radius, 20 percent grade climbing and high speed track switches are incorporated in the track extension plans.
The FlexiTrain system claims to offer the best features of personal and mass transportation, and doesn't need a lot of expensive new infrastructure. In a nutshell, here's the idea: Small individual electrically-powered vehicles for short trips, which can be connected together by means of intelligent mechanical couplings into larger hybrid-power units for longer journeys, using existing roads.
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