Personal Rapid Transit

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PRT cabin at London Heathrow Airport
Mountain coaster

Personal Rapid Transit ( PRT ) is a concept of a driverless, lane- guided passenger transport system that takes passengers to their destination individually on request without a stopover , without a timetable .

If it is used as a basic service in local public transport , it is a special form of public transport , similar to an on-call bus; if it drives like a privately run taxi, it is classified as individual transport .

term

In Germany, the term “cabin taxi” has been used instead of PRT since the 1950s, and accordingly a specific project was also called cabin taxi . However, since there were no other projects of this type, the US term PRT has been used in transportation science since the 1990s. Other names are "PAT" (Personal Automated Transport) and "podcar". The word “staff” in PRT is differentiated from the word “mass” in mass transit (local public transport, local public transport) and means “personal” in the sense of “individual”. From the point of view of transport science, however, the system as such does not belong to individual transport , but like taxis to public transport . It is actually both, something in between, a “public individual means of transport”.

description

In contrast to other fully automated public transport systems, passengers arrive at their self-determined destination in small cabins. He does not need to orient himself to a timetable, which is why some PRT manufacturers use the slogan: “You don't wait for the vehicle (or the company name), it is waiting for you.” In reality, this situation is of course dependent on the utilization of the system. In contrast to normal public transport, a locally underloaded station actually has the possibility that the cabins wait like a taxi queue. In a well-developed network, a passenger can go to any destination at a stop at any time. If the PRT fulfills these criteria as public transport , it is counted as a special form of public transport and, thanks to its energy-saving drive technology, represents an environmentally friendly alternative to cars .

The energy consumption is lower thanks to the cabs, which are lighter than a car, and the higher-level control system that optimizes the flow of traffic. No internal combustion engines are used in the track-guided PRT systems; all current systems are driven by linear or rotary electric motors. The energy is supplied via sliding contacts or exchangeable accumulators, or the cabin drive is passive (linear stator on the cabin, see below Vectus).

Depending on the system, the cabins travel at maximum speeds between 35 and 50 km / h. The resulting lower mechanical safety precautions allow a smaller and lighter construction compared to a car. The speed is determined by the safety distance to the preceding cabin in the convoy.

The so-called brickwall criterion is used for security . It is assumed here that, in the worst case scenario, when driving in a convoy, the predecessor stops suddenly and immediately (infinite braking acceleration, as if the car were leading up a wall). In this case, the successor should have sufficient distance to come to a collision-free standstill at maximum speed. In the 1970s there were still concepts aimed at coupling the vehicles while driving, since the distance becomes very small shortly before coupling, the risk of collision in the Brickwall criterion is too high. The distance for the Brickwall criterion results from the braking distance and is therefore dependent on the speed in the second power (quadratic). The throughput of the cabins per time has a computational maximum. The maximum speed results from the maximum throughput (multiplied by the actual distance), it is approx. 40 km / h. If the speed were to be increased above this maximum, the distance would increase so that the throughput, that is to say the transport capacity, would decrease if the safety criterion was met. If several cars are permanently coupled to one another (inseparably during the journey) to form a train, the throughput increases approximately (minus the car length) linearly with the number of cars. The average effective travel speed (door to door) in a large city is usually less than 30 km / h. This applies to both public transport and private transport.

The capacity, i.e. the number of people transported per time, of a route in one direction is calculated from the throughput of the cabins, multiplied by an assumed number of occupants. This value is hotly debated because it is measured against conventional public transport. For example, a maximum capacity of approx. 36,000 people per hour is specified for the Berlin S-Bahn, while a value above 5000 can hardly be achieved with PRT. The currently fastest PRT (Vectus) with a cabin throughput of the specified 1200 cabins would theoretically, i.e. H. with full four-person cabins, a capacity of 4800 people per hour. Certainly the cabins will not always fill up with direct trips from the periphery with several stations to the city center, even at peak times.

Representation of a possible PRT network: The blue rectangles mark the stations whose branched diversions enable through traffic.

At this point the differences to local public transport become clear. When the trains with the high capacity arrive at the periphery, the train, which weighs tons and can hold around 1000 people, often runs empty to the last station. This is not possible with PRT if empty journeys in one direction are necessary even in rush hour, since at least one direction is approached as required.

The number of occupants per cabin varies between one and about twelve people. In the case of smaller networks or test systems with a few stops, the requirements of individual transport are not sufficiently met. In order to guarantee the transport services nonetheless, when pilot systems are introduced in public operations, one is forced to design the cabin for a large number of people, which in turn reduces the attractiveness and goes against the actual principle of the PRT. That is why one speaks of a so-called people mover in the case of automated (driverless) systems with twelve or more occupants ; Similarities with the marshrutka then come to mind .

Historical projects

A first public fully automated transport system: Morgantown PRT of WVU 's not really "individual" because of the large cabins and is therefore referred to as "quasi-PRT"
Aramis test facility on Boulevard Victor in Paris, 1986

To this day, numerous systems with very different technologies have been tested and built. This project was supported by Richard Nixon as a demonstration project for a modern means of local transport and was built during the first oil crisis in 1974 and put into operation after a year. The relatively large cabins for 12 occupants and the small number of five stations in relation to the route network length of 14 km reduce the individual character of the system, so that it could almost be described as a people mover . In addition, the system works in two modes, depending on the time of day: on the one hand as a people mover, i.e. stopping at every station, clocked according to the timetable, and on the other hand in PRT mode on request directly to the destination.

Also in 1974, one of the first large PRT projects with the name Cabinentaxi with a 1.5 km long circular route was tested in Hagen (North Rhine-Westphalia) , but it was discontinued in the early 1980s. A descendant of this development was built in 1975 as a 578 m horizontal lift , called the Cabinenlift , in the Ziegenhain district hospital to connect the pre-care and aftercare clinic and remained in operation until 2002.

In France, Matra developed and tested the Aramis PRT system between 1973 and 1987 . There were several test facilities, first at Paris-Orly Airport and later on Boulevard Victor in Paris. Aramis initially consisted of four-seater cabins with rubber tires, which were driven by an electric rotary motor. Particularly innovative was the immaterial or electronic coupling, through which individual cabins were brought together like train parts, but could be separated at any time if there was a fork in the road. Due to technical difficulties as well as disagreement among the project partners, the original Aramis concept was modified so much that it became more and more similar to conventional local transport systems. Finally, the cabins should hold up to 20 people and two cars each should be mechanically linked. In 1987 Aramis was put aside for lack of money and the test facility on Boulevard Victor was shut down.

In the 1990s, American corporation Raytheon invested heavily in the development of a PRT system called the PRT2000 with similarly sized cabins, but failed in an offer to build a system in Illinois, near Chicago, when the cost was US $ 50 million - Exceeded $ per mile.

The University of Paderborn explored from 1997, a large taxi called RailCab on the rail network.

Current projects

London Heathrow Airport

At London Heathrow Airport Terminal 5 was the end of 2010, the first commercial PRT system by the manufacturer ATS Ltd called ULTra by BAA plc taken as a pilot project in operation. The construction of the routes was completed in October 2008. In the first test phase, 18 cabins will initially be used. Four adults and their luggage fit into a cabin. The PRT transports passengers from a more distant long-term parking lot to their terminal after they have entered their flight number. The battery-operated vehicles are designed for a distance of 4 km. If the pilot project is successful, it will be extended to the entire airport and surrounding hotels with 400 cabins. In 2010 it was the first commercially used PRT system worldwide.

Uppsala in Sweden

In terms of political engagement, Sweden has taken the lead. Here a network of interested municipalities called “Kompass” has pushed the topic far ahead. A comprehensive investigation by the Ministry of Infrastructure, in collaboration with Banverket, the Swedish Railway Authority, and other institutions has given the green light for pilot systems for public use in selected cities. A PRT system operated by linear motors has already been tested in Uppsala (Sweden) . This system, called Vectus PRT , a subsidiary of the Korean steel company POSCO , is the first rail-mounted system that has been successfully tested with modern safety requirements.

Suncheon in Korea

POSCO, the parent company of the subsidiary Vectus at the time, signed an agreement in September 2009 with the city of Suncheon City (approx. 20 km from the main POSCO plant) for the construction of a PRT network. It was originally supposed to be completed for the International Garden Expo 2013, but it did not succeed. The PRT system is now in operation. The PRT system has moved the parking lot away from the nature reserve, Wetland Park, and into the inland.

Masdar in Abu Dhabi

The largest PRT network planned to date has a length of 33.1 km and will serve 83 stations with 2500 cabins. The system is already in operation, but so far it has only been shuttled between 2 stations. The cabins of the Dutch company 2getthere , the so-called “pods”, are supplied with lithium-iron-phosphate batteries . It will be installed in Masdar , an eco-city , and other parts of Abu Dhabi in the United Arab Emirates .

criticism

capacity

With PRT, too, traffic jams occur when the capacity limit is reached. The advantage, however, is that it is easier to optimize the flow of traffic because you have a more direct influence on the vehicles. One can argue that with one person per PRT cabin, the capacity per lane cannot be much greater than that of a car, although this is mainly due to the fact that in real urban car traffic the safety distances are usually well below the limit. For safety reasons, such short distances cannot be achieved in a fully automated, driverless system. However, this also means a system-related higher security of PRT. Current systems that are in operation have a so-called "headway" greater than 6 s due to the not yet fully developed distance regulation, which significantly limits the capacity.

If a stop is overloaded during rush hour and all stop lanes are occupied, the stop cannot be approached. Either the vehicle waits and blocks the lane, or it drives on and the passengers who actually wanted to get off are forcibly carried on. However, this should not happen in normal operation, so that only the first option remains.

One advantage is that vehicles that are used by commuters in the morning and evening do not park around the rest of the time, but can serve as a means of transport for others. However, as with other means of urban transport, the capacity must be designed for the rush hour in the morning and late afternoon, which lasts just a few hours .

Swedish PRT Spårtaxi (photo montage)

Space requirements and energy

PRT systems reduce the number of parking spaces required, but less the number of vehicles (in operation) or lanes required to achieve the same maximum transport capacity as the existing individual traffic. However, it can be said that the design of the cabins, which has been optimized for passenger transport, means that much lower space and energy consumption can be achieved. In contrast to electric cars, the cabins can be fed via busbars, which means that the traction battery is no longer necessary, which currently still makes a significant contribution to the CO 2 balance of electric cars.

Cityscape

The space requirement can also be reduced by an increased route, which, however, unlike in the photo montage by Spårtaxi, would be much more massive in reality and thus less acceptance of the cityscape would be achieved.

Citizens have already opposed new means of transport driving past their windows in an elevated position and looking into their rooms. For this reason, z. B. Cable car systems in urban areas have failed.

economics

Such systems are very expensive to build due to the many small cabins. They do not offer the capacity of other public transport. Despite the similarly high costs as car traffic, they do not offer the convenience of transfer-free traffic directly to the front door, but stations are still required at a smaller or larger distance. The smaller the distance, the higher the construction costs. As with bus systems, there will have to be a distance between the stops of around 300 m.

Thus, all such cabin systems are limited to very few exceptional cases, such as. B. at airports to connect the terminals. But for reasons of economy and capacity, a minimum cabin size of approx. 20 people is required. In addition, the small cycle intervals of a few seconds that are possible with cabin systems are not even necessary in practice. A gap of five or even up to 10 minutes is still well received by passengers. This means that no specific traffic is required, but with a dense cycle of two to five minutes, as is the case with subway systems in large cities, changing between the lines is easily accepted.

PRT versus autonomous driving

With the advancing technology development in the field of autonomous driving, the complex routes and lane guidance technologies of the PRT systems appear obsolete at first glance: Driverless operation could also be possible on existing roads. On the other hand, PRT systems could also use more cost-effective autonomous driving technologies and still use the advantages of isolated operation on their own routes. Compared to electric, autonomous vehicles, the track-guided PRT eliminates the need for a traction battery thanks to a conductor rail.

See also

Web links

Individual evidence

  1. ↑ "Everywhere nudges and irritations" . In: Der Spiegel . No. 19 1973 ( online - 7 May 1973 ).
  2. ↑ Anton Redfors: A Field Study of PRT in Shanghai . December 2009, p. 17 (English, PDF, 2 MB [accessed on November 27, 2011] Bachelor thesis at the Institute for Physics and Astronomy at Uppsala University ).
  3. ↑ Sylke Grede: Cabin lift at the hospital: In a floating taxi. In: hna.de. August 10, 2012, accessed June 10, 2016 .
  4. ^ Bruno Latour: Aramis or the Love of Technology . Harvard University Press, Cambridge (Massachusetts) / London (England) 1996, ISBN 0-674-04323-5 Brief description & structure (English)
  5. ↑ The first PRT initiative in Korea announced  ( page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. (PDF; 266 kB), September 2009@1@ 2Template: Dead Link / www.prtstrategies.com  
  6. ↑ National (ae): Fast Track to Abu Dhabi's future ( Memento of the original from February 10, 2009 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , August 30, 2008 @1@ 2Template: Webachiv / IABot / www.thenational.ae
  7. ↑ 2-wheel Personal Rapid Transit .