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The design concepts and engineering challenges of PRT are well understood, but questions remain about its actual production and operation costs, its safety, aesthetics, and acceptance in a public installation. The concept is considered controversial partly because there has never been a real-world installation on which to base firm predictions of key variables such as cost and ridership. Past failures have been caused by: lack of financing; concerns about cost overruns; conflicts with regulatory agencies; political interference in the design requirements; and flaws in design and/or engineering. There is also opposition from advocates of other transport modes. Two projects are currently under development: one at Heathrow Airport in London {Link without Title} , scheduled to come into operation in 2007 ; and another is planned at Dubai International Financial Center in Dubai scheduled to be operational in 2008 . OVERVIEW PRT has similarities to and differences from other forms of transport. To compare the proposed features: HISTORY The concept originated with Don Fichter, a city transportation planner, and author of a 1964 book entitled "Individualized Automated Transit in the City". The Morgantown Personal Rapid Transit project has been in continuous operation at West Virginia University in Morgantown, West Virginia since 1975 , with about 15,000 riders per day ( As Of 2003 ). The vehicles are rubber-tired and powered by electrified rails. Steam heating keeps the elevated guideway free of snow and ice. Most WVU students habitually use it. This system was not sold to other sites because the heated track has proven too expensive. The Morgantown system demonstrates automated control, but authorities no longer consider it a true PRT system. Its vehicles are too heavy and carry too many people, making it more similar to Light Rail schemes. Most of the time it does not operate in a point to point fashion for individuals or small groups, running instead like an automated people mover or elevator from one end of the line to the other. It therefore has reduced capacity utilization compared to true PRT. Morgantown vehicles also weigh several tons and run on the ground for the most part, with higher land costs than other systems. The Aramis Project in Paris , by aerospace giant Matra , started in 1967 , spent about 500 million francs, and was cancelled when it failed its qualification trials in November 1987 . The designers tried to make Aramis work like a "virtual train," but control software issues caused cars to bump unacceptably. A project called ''Computer-controlled Vehicle System'' (CVS) operated in Japan from 1970 to c.1978. In a full scale test facility, 84 vehicles operated at speeds up to 60 km/h on a 4.8 km guideway; 1 second headways were achieved during tests. Another version of CVS was in public operation for six months during 1975–76. This system had 12 single-mode vehicles and 4 dual-mode vehicles on a one mile track with five stations. This version had over 800,000 passengers. CVS was cancelled when Japan's Ministry of Land, Infrastructure and Transport adjudged it unsafe under existing rail safety regulations, specifically in respect of braking and headway distances. In Germany , the '' Cabinentaxi '' project, a joint venture from Mannesmann Demag and MBB , created an extensive PRT development in the 1970-80s considered fully developed by the German Government and its safety authorities. This project was canceled when a disagreement over the site for the initial implementation coincided with non-defense budget cuts by the German government. Raytheon invested heavily in a system called PRT2000 in the 1990s , and failed to install a contracted system in Rosemont, near Chicago, when its estimated costs exceeded $50,000,000 per mile. This system may be available for sale by York PRT. In 2000, rights to the technology reverted to the University Of Minnesota , and were purchased by Taxi2000. The UniModal (also known as SkyTran ) project, originated by Douglas Malewicki, proposes using Inductrack passive Magnetic Levitation in vehicles with few moving parts to achieve speeds of 100 mph (161 km/h). Its assumptions of capacities are based on these speeds and on half-second headways, and includes many other hypothetical features such as Speech Recognition . Malewicki freely acknowledges that this is at present a paper concept, and no prototype yet exists. In 2002 , 2getthere, a consortium of Frog Navigation Systems and Yamaha, operated "CyberCabs" at Holland's 2002 Floriade festival. These transported passengers up to 1.2 km on Big Spotters Hill. CyberCab is like a Neighborhood Electric Vehicle , except it steers itself using magnet guidance points embedded in the lane. In 2003 , Ford Research proposed a Dual-mode system called PRISM. It would use public guideways with privately-purchased but certified dual-mode vehicles. The vehicles would be less than 600 kg (1200 lb), allowing small elevated guideways which could use centralized computer controls and power. In January 2003 , a prototype ULTra ("Urban Light Transport") system from Advanced Transport Systems Ltd in Cardiff, Wales was certified to carry passengers by the UK Rail Inspectorate on a 1 km test track. It had successful passenger trials and has met all project milestones for time and cost. The ULTra system differs from many other systems in its focus on using off-the-shelf technology and rubber tires running on an open guideway. This approach has resulted in a system that is more economical than designs requiring custom technology. ULTra was recently (October, 2005) selected] by BAA Plc for London's Heathrow Airport . This system is planned to transport 11,000 passengers per day from remote parking lots to the central terminal area. PRT is favored because of zero on-site emissions from the electrically powered vehicles. PRT will also increase the capacity of existing tunnels without enlargement. BAA plans begin operation by the end of 2007 and to expand the system in 2009. Vectus Ltd., a Korean/Swedish consortium, is constructing (2006) a test track in Sweden. PRT SYSTEM DESIGN , a PRT concept, superimposed on a real photograph]] There are currently no agreed-upon standards in system design. Among the handful of prototype systems — and the larger number that exist on paper — there is a substantial diversity of design approaches, some of which are contentious. Vehicle Design Vehicle weight influences the size and cost of a system's guideways, which are in turn a major part of the capital cost of the system. Larger vehicles are more expensive to produce, require larger and more expensive guideways, and use more energy to start and stop. If vehicles are too large, point-to-point routing also becomes uneconomical (for example, when the system at West Virginia University moved from 6-passenger to 20-passenger vehicles, point-to-point operations were largely abandoned). Against this, smaller vehicles are more affected by air resistance, which dominates the energy cost of keeping vehicles moving at speed. Larger motors are also generally more efficient than smaller ones. The number of riders who will share a vehicle is thus a key variable. Until a public system is operating, this can only be estimated; ridership cannot be extrapolated from fixed-route systems such as buses or trains. One possible prototype for personal point-to-point travel is the private automobile: the U.S. averages 1.16 persons per vehicle, and an average of below 2 is common in most industrialized countries. Thus, some designers claim that the optimum vehicle size is 2 passengers (or less) and some systems (notably UniModal / SkyTran) have been designed this way. Others consider that larger vehicles are needed, for example to accommodate families or disabled passengers. As of 2006 all systems known to be under active development use 4-passenger vehicles. Propulsion All current designs are powered by Electricity , generally transmitted via lineside conductors rather than using on-board batteries, to reduce vehicle weight. According to designer of Skyweb/Taxi2000, J.E. Anderson, the lightest-weight system is a Linear Induction Motor (LIM) on the car, with a stationary conductive rail for both propulsion and braking. LIMs are used in a small number of rapit transit applications, but most PRT designs use rotary motors. Switching Most designers avoid Track Switching , preferring vehicle-mounted switches or conventional steering. This allows closer spacing of vehicles without the time delays inherent in track switching. Infrastructure Design Guideways There is some debate over the best type of guideway. Among the proposals are beams similar to monorails, bridge-like trusses supporting internal tracks, and cables embedded in a roadway. Most designs put the vehicle on top of the track, which reduces visual intrusion and cost as well as facilitating ground-level installation. Overhead suspended vehicles are said to unload the skins of the vehicle, which can therefore be lighter since many materials are stronger in tension than they are in compression. An overhead track is necessarily higher, but may also be narrower. Most designs use the guideway to distribute power and data communications, including to the vehicles. Following some issues with prototypes many also aim to be self clearing in bad weather. Stations Stations are usually proposed to be frequent, and located on side tracks so that through traffic can bypass vehicles picking up or dropping off passengers. Each station might have multiple berths, with perhaps 1/3 of the vehicles in a system being stored at stations waiting for passengers. Embarkation stations are not envisaged to include facilities such as rest rooms. For elevated stations, an elevator may be required for accessibility. Some designs have included substantial extra expense from the track needed to decelerate and accelerate from stations. In at least one system, Aramis, this nearly doubled the width and cost of the required right-of-way and caused the nonstop passenger delivery concept to be abandoned. Other designs have schemes to reduce this cost, for example merging vertically to reduce footprint. Operational Characteristics Headway Distance Spacing of vehicles on the guideway influences the maximum passenger capacity of a track, so designers aim to minimize the ''headway,'' the distance between vehicles. Computerized control theoretically permits closer spacing than the two-second headways recommended for cars at speed, since multiple vehicles can be braked simultaneously. There are also prototypes for automatic guidance of private cars based on similar principles. Very short headways are controversial. Some regulators (e.g. the British Rail inspectorate, regulating ULTra) are willing to accept two second headways. In other jurisdictions rail regulations apply to PRT systems (See CVS, above); these typically calculate headways in terms of absolute stopping distances and may make PRT systems uneconomical. No regulatory agency has yet endorsed headways as short as one second. Regulators may be willing to reduce headways with increased operational experience. Capacity PRT is usually proposed as an alternative to rail systems, so comparisons tend to be with rail. Since there are no full-scale installations, capacity calculations are based on simulation and modelling and are contested by skeptics. PRT vehicles seat fewer passengers than trains and buses, and must offset this by higher average speeds and shorter headways. Proponents assert that equivalent or higher overall capacity could be achieved by these means. With two-second headways, an average of 1.5 persons per vehicle implies a maximum capacity per guideway route of 2,700 passengers per hour, dependent on having sufficient vehicles available. In simulations of rush hour or high-traffic events, about 1/3 of vehicles on the guideway need to travel empty to resupply stations with vehicles in order to minimize response time. Light rail systems can achieve capacities over 7,500 passengers per hour under normal operations. Heavy rail subway systems regularly transport 12,000 passengers per hour or more. Neither light nor heavy rail scales well for off-peak operation. Travel Speed For a given peak speed, point-to-point journeys are quicker than scheduled stopping services. While a few PRT designs have operating speeds of 60 mph, most are in the region of 25-45 mph. Rail systems generally have higher maximum speeds, typically 55-80 mph and sometimes well in excess of 100 mph; but average travel speed may be reduced by the need to stop at all stations, as well as the need for passengers to transfer. Ridership Attraction If PRT designs could deliver the claimed benefit of being substantially faster than cars in areas with heavy traffic, simulations suggest that PRT might attract significantly higher than the predicted mode switch from private motoring than is the case for other proposed public transit systems (figures between 25% and 60% have been discussed). Against this, the relationship of delays to traffic density for road travel is observed to be non-linear and the congestion delays which give rise to the predicted attraction may be eroded. London's Congestion Charge achieved approximately 20% reduction in private motor traffic, with an immediate and measurable improvement in journey times for all road transport in the City. This was achieved without substantial up-front investment, although revenue raised has been re-invested in additional public transport capacity. Control Algorithms One possible control algorithm places vehicles in imaginary moving "slots" that go around the loops of track. Real vehicles are allocated a slot by track-side controllers. On-board computers maintain their position by using a Negative Feedback Loop to stay near the center of the commanded slot. One way vehicles can keep track of their position is by integrating the input from speedometers, using periodic check points to compensate for cumulative errors. Another style of algorithm assigns a trajectory to a vehicle, after verifying that the trajectory does not violate the safety margins of other vehicles. This system permits system parameters to be adjusted to design or operating conditions. may use use slightly less energy. The maker of the ULTra PRT system reports that testing of its control system shows lateral (side-to-side) accuracy of 1 cm, and docking accuracy better than 2 cm. Safety Computer control is considered more reliable than drivers, and PRT designs should, like all public transit, be much safer than private motoring. Most designs enclose the running gear in the guideway to prevent derailments. Grade-separated guideways would prevent conflict with pedestrians or manually-controlled vehicles. Other public transit Safety Engineering approaches, such as redundancy and self-disagnosis of critical systems, are also included in designs. The Morgantown system, more correctly described as an Automated Guideway Transit system (AGT), has completed 110 million passenger-miles without serious injury. According to the U.S. Department of Transportation, AGT systems as a group have higher injury rates than any other form of rail-based transit (subway, metro, light rail, or commuter rail) though still much better than ordinary buses or automobiles. As with many current transit systems, passenger safety concerns are likely to be addressed through CCTV monitoring, and communication with a central command center from which engineering or other assistance may be dispatched. Cost Characteristics PRT designs generally assume dual-use rights of way, for example by mounting the transit system on narrow poles on an existing street. If dedicated rights of way were required for an application, costs could be considerably higher. If tunnelled, small vehicle size can reduce tunnel volume compared with that required for an Automated People Mover (APM) . Dual mode systems would use existing roads, as well as special-purpose PRT guideways. In some designs the guideway is just a cable buried in the street (a technology proven in industrial automation). Similar technology could equally be applied to private automobiles. A design with many modular components, mass production, driverless operation and redundant systems should in theory result in low operating costs and high reliability. There are already some operational driverless transit systems, mostly at airports and tourist attractions. Cost data from these small-scale systems indicates that while automation reduces labor costs by eliminating drivers, these savings are eroded by increased vehicle maintenance and system monitoring. It is not clear whether larger systems would have the same maintenance and monitoring inefficiencies. Predictions of low operating cost generally depend on low operations and maintenance costs (O&M). Whether these assumptions are valid will not be known until full scale operations are commenced since assumptions regarding reliability cannot be proven by prototype systems; U.S. federal data shows that O&M costs are nearly constant per seat for a wide variety of systems: buses, trains, aircraft and private automobiles. Low operating cost projections also depend on relatively high capacity utilization (for a public transport system) delivered through on-demand service. Some planners dispute the cost-estimates of PRT when compared to Light Rail systems, whose costs vary widely with non-grade-separated streetcars being relatively low cost and systems involving elevated track or tunnels costing up to US$ 200 million per mile. Systems such as streetcars, which run over the road network, and buses, require no further rights of way, which can represent a substantial cost saving over those requiring new, dedicated routes. Ridership and cost For scheduled mass transit such as buses or trains, there is a fundamental tradeoff between service and cost. This is due to the fact that buses and trains must run on a predefined schedule, even during non-peak times when demand is low and vehicles run nearly empty. For this reason, transportation planners typically control costs by attempting to predict periods of low demand, running on reduced schedules and/or with smaller vehicles at these times. This, however, increases wait times for passengers. In many cities, trains and buses do not run at all at night or on weekends, because the low demand does not justify the cost. PRT vehicles, in contrast, would only run in response to demand, allowing 24-hour service without many of the cost implications of scheduled mass transit. OPPOSITION AND CONTROVERSY Opposition has been expressed to PRT schemes and their proponents based on a number of concerns: Technical feasibility debate Regulatory concerns Possible regulatory concerns include emergency safety, headways, and accessability for the disabled. If safety or access considerations require the addition of walkways, ladders, platforms or other emergency/disabled access to or egress from PRT guideways, the size of the guideway is substantially increased. Because minimizing guideway size is important to the PRT concept and costs these concerns may be significant barriers to PRT adoption. The US and Europe both have legislation mandating disabled accessibility for public transport systems. For example, the California Public Utilities Commission states that its "Safety Rules and Regulations Governing Light Rail Transit" (General Order 143-B) and "Rules and Regulations Governing State Safety Oversight of Rail Fixed Guideway Systems" (General Order 164-C) are applicable to PRT Both documents are available online [http://www.cpuc.ca.gov/static/documents/i_go.htm . The degree to which CPUC would hold PRT to "light rail" and "rail fixed guideway" safety standards as a condition for safety certification is not clear. Other concerns Concerns have been expressed about the visual and environmental impact of (especially elevated) guideways. The 2001 OKI Report stated that Skyloop's elevated guideways and elevated stations would be visual pollution that neighborhoods would challenge in an Environmental Impact Statement (EIS). Some in the business community in Cincinnati were opposed to Skyloop's elevated guideway because it would remove potential customers from the street level. As with other modes of public transit, there are also concerns about policing against terrorism and vandalism. Israeli proponents say that PRT may protect against terrorism by reducing the scope of vehicle that can be attacked. Some have also objected to PRT promotion on the grounds that it is a distraction from other, more proven transit solutions. Objectors claim that advocacy for PRT has reduced support for other alternatives to private motoring, with the result that neither alternative has been implemented. SEE ALSO
EXTERNAL LINKS Pilots and prototypes
Proposals
Advocacy
PRT Skepticism and Criticism PRT design superimposed on a real street.]]
REFERENCES Additional references
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