Talk:Personal rapid transit/Pro and con

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[edit] Arguments for and against PRT

[edit] Advantages

  • By design and definition PRT includes:
  • Non-stop rides from origin to destination
  • On demand transportation, meaning no schedules or waiting
  • Travel is alone or in self-selected groups
  • Grade separation
  • Stations offline on sidings
  • PRT systems have numerous design features to prevent accidents: grade-separated guideways, wheels captured by the track to prevent derailment, automated control (decentralized in most modern designs), redundant safety-critical parts, central power with backups, periodic, often automatic inspections of safety equipment (see also "Control algorithms," above). So, widespread PRT use could reduce accidents involving cars, and provide more reliable service.
  • In theory, PRT systems will not delay commuters with gridlock or traffic jams. This should make them more attractive than automobiles. Methods vary, but most designs plan to move at or near the maximum system speed more than 95% of the time, including at "rush hour." PRT systems therefore offer transportation two to fifteen times faster than autos, buses or trains (depending on assumptions).
  • Per unit of passenger-distance, the traits of PRT enable proponents to cost-out PRT systems at 3 to 10% of automobiles.
  • With reasonable assumptions, PRT systems are said to have better capital use than other systems. Compared to light rail, a single PRT line integrated into an existing multimodal transit system (not a PRT network) is said to have a comparable passenger capacity to a train or freeway, fifty-fold lower cost of rights of way, 60% more trips per seat, and as an automated system that does not require rides with strangers, substantially lower costs of ownership because it does not need drivers or transit police. If PRT captures more riders, uses semi-automated track-assembly or expands into a network, these effects multiply.
  • Parking costs and space are not required, because the vehicles remain in use. They also eliminate a need for a driver's license, gas, insurance or sobriety. Of course, temporary storage of vehicles requires some space (and thus cost), because at low ridership hours, not all vehicles would be in use. In any case, much less space is needed than in other transportation systems.
  • In theory, PRTs' lower costs can be completely offset by fares, eliminating government subsidies and enabling private companies to compete to provide even better systems.
  • Since most PRT ideas include automated vehicles, passengers can relax and do other things while riding. This trivial-sounding benefit frees an amount of time with a value of hundreds of billions of dollars per year, an advantage shared by most transit systems.
  • PRT could eliminate much of the world's urgent dependence on oil. Liquid fuels could be reserved for heavy transport. If the need for oil causes wars, this could save more lives and money than any other feature.
  • PRT systems often have shorter completion times than conventional transportation systems: waits of months rather than years. (pp. 13-14 at [1])
  • PRT systems usually operate from the electrical grid, and are therefore less polluting and less expensive than even fuel-cell automobiles. Because it is electrically powered, pollution occurs at a power plant that can be more easily monitored or improved than automobiles.
  • Transit police are not required. Criminals cannot wait for a vehicle to arrive, because they would not know the car's destination. Most designs include a panic button that takes the unit to a police station. Stops and (in some systems) vehicles would have video cameras.
  • The PRT concept has been studied and validated by a number of governments, including the United States,[2] West Germany (resulting in Cabinentaxi) and the European Commission [3] (resulting in the ULTra system). Some PRT systems have been proven--in addition to Cabinentaxi and ULTra at Cardiff, Wales, there is West Virginia University's automated Morgantown Personal Rapid Transit peoplemover, which operates on a guideway network with offline stations, and is able to operate in on-demand mode. ULTra now has demonstrated cost figures ([4], pp. 13-16), and has been selected for installation at Heathrow Airport (see History, above).
  • Simulations show that PRT can squeeze the transportation of up to four lanes of limited-access highway into the ground-space of poles spaced thirty feet apart. Laid in a grid with 1 mile or less of separation between parallel guideways, and stations spaced three-quarters of a mile or less apart, it should solve most cities' traffic problems, enabling growth from the low densities at which autos are practical into the densities at which trains become practical. PRT proponents therefore say that the system offers hope for solving transportation problems that conventional transit options cannot. Chicago is a low-density city with fully-realized train, freeway, and bus plans. These have failed, and the city is now (as of 2003) said to be investigating PRT.
  • Using PRT could let an impoverished yet technical country leap-frog past many more-developed countries' congestion, safety and pollution problems.
  • Should estimates of low PRT capital costs be realized, less investment would need to be recouped. Therefore, PRT could be affordable even for low-density areas, such as urban single-family residential zones. The implication for urban planners is that all areas within the PRT coverage area, of all densities, could be affordably served by PRT. In effect, this transit service would be similar to the distribution of water or electricity by public utilities. So, policy decisions regarding land use and economic development could be made more purely according to desired land uses and economic outcomes, with less attention to the needs of the transit system. Indeed, PRT is gaining support among advocates of smart growth urban policies[5].
  • An initial PRT system need not be large (to overcome network effects), as lower unit costs means it is possible for a smaller network to recoup its capital cost.[6]
  • Advocates say that "fatal" flaws cited by critics are actually identifiable and correctable errors made in particular designs, such as Raytheon's[7] and Morgantown[8]. Perceived limitations in PRT service are usually misundertanding of PRT operating concepts, say proponents. For example, they say it is incorrect to assume that an expected 100 passengers requires a large station with 100 vehicles ready to go at the same time. Instead, unscheduled and on-demand service means the 100 people would be served a few at a time as they enter the station, not simultaneously.
  • The beginning of the section below (Cons) has a discussion of the OKI report that recommended against PRT. After that report was submitted, Taxi 2000 and the Sky Loop committee wrote an extensive rebuttal that responded to the OKI report point by point. PRT evaluations are often performed by engineers who specialize in rail transit. The technologies diverge on many issues. In the case of the OKI report, the rail transit consultants redesigned the proposed system, and then criticized their redesign, assuming standard rail technologies throughout.

[edit] Cons

Opposition to the PRT concept falls into four main categories

  • On grounds of technological feasibility:

The 2001 Ohio, Kentucky, Indiana (OKI) Central Loop Report [13] compared the Taxi 2000 PRT concept proposed by the Skyloop Committee[14], to other transportation modes (bus, light rail and vintage trolley). Consulting engineers with Parsons Brinckerhoff[15] found the Taxi 2000 PRT system had "...significant environmental, technical and potential fire and life safety concerns..." and the PRT system was "...still an unproven technology with significant questions about cost and feasibility of implementation." It was this report which prompted the extensive rebuttal mentioned in the previous section (Pros).

Vukan R. Vuchic, Professor of Transportation Engineering at the University of Pennsylvania [16] described what he believes are problems with the PRT concept, in the article "Personal Rapid Transit: An Unrealistic System," Urban Transport International (Paris), (No. 7, September/October, 1996) [17]:

"The PRT concept is imagined to capture the advantages of personal service by private car with the high efficiency of rapid transit. Actually, the PRT concept combines two mutually incompatible elements of these two systems: very small vehicles with complicated guideways and stations. Thus, in central cities, where heavy travel volumes could justify investment in guideways, vehicles would be far too small to meet the demand. In suburbs, where small vehicles would be ideal, the extensive infrastructure would be economically unfeasible and environmentally unacceptable."

It should be noted that J. Edward Anderson and Dennis Manning have written responses to this article ([18],[19]), which proponents say address Vuchic's concerns.

In another article, "Personal Rapid Transit Works in Simulation Only - An Answer to Professor J. Edward Anderson" (in the Urban Transportation Monitor, December 20, 1996), Vuchic commented on what he sees as PRT's technical problems[20]:

"There is a fascination with short headways PRT could operate. Theoreticians like to analyze "subsecond headways" which, even if technically feasible, would neither be desirable nor achievable for many vehicles in sequence. Off-line stations would, presumably, allow undisturbed passage of mainline traffic while vehicle alighting/boarding is performed. But if, for example, a train in Chicago unloads 75 persons at the PRT station, they will need some 40 PRT vehicles, and that boarding would take a much longer time than boarding two AGT or one light rail vehicle. Capacity of boarding can be increased by building long platforms, but large structures make stations even less acceptable in many urban settings. Simulation may show that station operations are fast, but that depends on how realistic are the assumptions used in the simulation model..."
"...The common gap between theoreticians and practitioners is particularly great with respect to PRT systems: the PRT concept attracts the interest of some vehicle designers and control engineers, and a number of operations researchers find challenges in optimizing individual operational processes. However, this concept has never found the support of persons involved in urban transportation planning, or in the design and operation of real world transit or taxi systems..."

What Prof. Vuchic's 'Chicago train' example describes is known as a "pulse" or surge problem. A discussion between Vuchic and J.E. Anderson on this subject can be found in "PRT Pulse (or Surge) Problem Commentary", 1996.

In "Personal Rapid Transit Works in Simulation Only," Professor Vuchic says this about "dual-mode PRT":

"During the 1970s there were serious proposals for development of "dual-mode" systems with vehicles running on guideways or driven on streets. When GM and others attempted to design such guideways and ramps for a specific city, most of the "system assumptions" had to be modified so much that it became clear the system would not be feasible."

J. Edward Anderson has responded to this article as well, which proponents say addresses Vuchic's concerns, which they say grew out of misunderstanding PRT operating characteristics.

Denver International Airport's baggage handling system, an automated system similar in concept to PRT but based on a different technological approach, failed to work properly due to inadequate planning[21]. After $186 million and years of trying to fix the system, the task is now handled by humans: 'It wasn't the technology per se - it was a misplaced faith in it,' said Richard de Neufville, a professor of civil and environmental engineering and engineering systems at the Massachusetts Institute of Technology. De Neufville said the builders imagined that their great creation would work well even at capacity, leaving no room for the errors and inefficiencies that are inevitable in a complex enterprise."[22]

  • On regulatory grounds:

Quite apart from the technical feasibility of PRT is the issue of whether such systems would be approved (licensed) by regulatory agencies to carry passengers. Regulatory concerns generally include emergency safety, headways, and accessibility for the disabled.

Although headway concerns have been addressed in controlled testing or simulations, emergency or wheelchair access remains a problem. While vehicles themselves are accessible, and stations can be made accessible with elevators, most "narrow guideway" elevated PRT systems have no emergency escape routes built into the guideway. Whereas grade-separated bus or rail passengers can exit a transit vehicle in an emergency and follow the elevated track, walkway, or tunnel, PRT passengers would be stranded in place.

If safety or access considerations require the addition of walkways, ladders, platforms or other emergency/disabled access to PRT guideways, the size of the guideway is substantially increased. Because minimizing guideway size is so crucial to the PRT concept (see aesthetic objections, below) these considerations remain significant barriers to PRT adoption.

Japan developed an advanced PRT system labeled "CVS" (Computer-controlled vehicle system) during the early 1970s. One-second headways and emergency braking were demonstrated successfully on the test track. However, plans for application stalled in part because the Ministry of Transport imposed the same safety standards for PRT (and AGT, or Automated Guideway Transit) as applied for all "trackguided" systems. This ruled out lightweight vehicles to permit low-cost guideway construction, and "close-headway" operation to permit high passenger capacity [23].

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 [24]. Both documents are available online [25]. 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.

In the US, any PRT system would have to be ADA compliant (vehicles, stations, and emergency access for guideways) and satisfy local fire and emergency concerns.

  • On grounds of aesthetics, perceived externalities, or quality of service:

A Cincinnati Post editorial (08-21-01) expressed the following opinions about the Skyloop PRT proposal:

:: "Our skepticism is grounded in more than the fact that this is an unproven technology:

:: "We hold with those who argue that it would be a mistake to take any more pedestrian traffic off street level..."

:: "No matter how handsome the design, an elevated system would be inherently ugly - and disruptive at points where it would intersect with downtown's historic buildings..."

:: "It seems doubtful that such a system could do much to move crowds following Reds and Bengals games or other major events."

These views were echoed by Cincinnati engineering director John Deatrick and architect Michael Shuster, in an article announcing OKI rejection of PRT on a 14-8 vote, "OKI rejects 'Sky Loop' Elevated Rail System" (9/26/01).[26]

  • On political or philosophical grounds:

Transit advocate Ken Avidor said in a guest editorial in the Seattle Post Intelligencer[27], "Basically, PRT is a stalking horse for the highway construction industry. PRT proponents can say things that the highway boosters could never say, such as "People don't like to ride with strangers." {sic} [28]. This anti-transit propaganda divides and conquers the opposition to highway projects." To support this view Avidor points to statements or activities by PRT proponents regarding light rail transit. Some have questioned the financing or effectiveness of light rail projects: environmentalist Emory Bundy[29]; former U.S. Department of Transportation railroad official Sheffer Lang (1927-2003)[30] [31]; David Morris of the Minnesota Institute for Local Self-Reliance[32]; Dr. J.E. Anderson [33]. Some have campaigned against public funding for light rail, and some PRT websites carry anti-light rail messages [34]. The group Coalition for Effective Transportation Alternatives[35] (CETA) favors bus rapid transit over the light rail project of the Seattle-area regional transit agency Sound Transit; CETA has prominent PRT proponents as members,[36] including Professor Jerry Schneider[37] and Emory Bundy[38].

Proponents say they are seeking to increase the available number of transit options, and so performance or cost comparisons to current modes such as light rail are inevitable. Advocates link PRT to reduction in road congestion[39] and decreased reliance on private cars, which they say would remove the need for highway expansion.[40] Proposals have been made to deploy PRT in conjunction with existing rail stations[41] and other transit centers.[42]

{{Uncategorized|October 2006}}

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