ATRA IG Viewpoint

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BlogIT is the Blog on Innovative Transit, as published on behalf of the ATRA Industry Group. It is a new initiative intended to allow ATRA IG to share its views on issues in the advanced transit industry.

BlogIT-004: PRT – A Future Solution or Relic of the Past?

The term “personal rapid transit” (PRT) has been around for decades – probably originating in the 1950s or 60s. What was meant by the term may have been unclear, however, since the Morgantown group rapid transit (GRT) system, which debuted in 1975, was called PRT. In his 1978 book “Fundamentals of Personal Rapid Transit” Jack Irving described PRT as follows:

PRT would be a public transit system of small (three- to six-passenger) vehicles travelling automatically on exclusive guideways, separated from street and pedestrian traffic. The traveler and his companions would be assigned a private vehicle, not shared with strangers, to take them on a nonstop no-transfers trip from their origin station to their destination station anywhere in a large urban area…

It has taken decades for modern systems called PRT to finally emerge and all of them stray from the above definition in some way. The Ultra PRT system in operation at Heathrow Airport and the 2getthere system at Masdar City both experience and facilitate ridesharing in peak periods. This reduces waiting and increases capacity at critical times and is an important feature not covered by Irving’s PRT definition (but addressed in his book which discusses hybrid PRT/GRT service). Furthermore, recent studies have shown organized ridesharing, including some intermediate stops, can be critical to boosting capacity in high-demand scenarios. Multiple class systems have been envisioned wherein riders can pay per vehicle to avoid sharing or intermediate stops, or per ride to save money by sharing. It has been suggested that the difference between PRT and GRT is better defined by the presence or absence of ridesharing than by vehicle size.

The Vectus PRT vehicles at Suncheon have six seats and room to accommodate an additional three standees, clearly assuming ridesharing will take place. The Mexican Modutram GRT system has an airport vehicle that allows standees and a six-seat urban vehicle that can be coupled into a two-vehicle train.

While Irving’s definition of PRT was later adopted by ATRA (with some minor changes), it is clear that modern PRT systems are finding reasons to stretch the definition. While “true” PRT systems undoubtedly have their place, it seems more likely that applications will continue to blur the boundaries between PRT and GRT. Is there a better name that will define these new systems adequately to separate them from more traditional systems and yet not be too limiting?

The City of San José coined the term “automated transit network” (ATN) in their 2012 feasibility evaluation for the San José Minéta International Airport. However, it implied that the term ATN was synonymous with PRT. In contrast, many ATRA members have come to view the acronym ATN as an umbrella term encompassing both PRT and GRT. ATN is defined by the three words in its name:

  • Automated (driverless)
  • Transit (excludes private driverless cars)
  • Network (access points are linked by a web of routes)

While on-board switching and small vehicles are attributes favored by many, they are not included in the definition of ATN. Thus both the Morgantown and Rivium GRT systems with their 20+ passenger vehicles are clearly included in the definition.

Since the definition of PRT is proving somewhat restrictive and since recently-deployed systems have not adhered well to this definition, ATRA is proposing moving towards adopting the term ATN as encompassing both PRT and GRT concepts and using this term more widely. This, however, does not in any way preclude the use of PRT or GRT when necessary to distinguish between these two modes. So, while many ATRA members may still believe PRT is an important future solution, the term ATN is gaining traction and better describes the range of technologies being deployed.

Peter Muller
ATRA President


BlogIT-003: The Heathrow Pod

The Heathrow pod is Ultra Global’s innovative Personal Rapid Transit (PRT) system at London’s Heathrow Airport, the service provides passengers transport between the airport’s Terminal 5 and a designated business car park. The PRT system has been open since May 2011 and has carried close to a million passengers. Mark Griffiths is Ultra Global’s Head of Operations and has been in charge of the team of controllers and technicians responsible for the day to day running of the system. Some of the stats from the system include:

  • Saved 200 tonnes of Co2 from the previous bus service
  • Has taken 70,000 bus journeys off of Heathrow’s congested roads each year
  • Has been voted the best passenger service on the airport campus
  • The pods at Heathrow have travelled over 2 million autonomous kilometres

The Heathrow pod

How long is the operation at Heathrow?
We operate in line with the operating hours of the airport, the first flight out of Terminal 5 is at 0630 and the last one arrives back around 2230. As a consequence for the majority of the week we operate from 0300 in the morning to pick up the first passengers arriving at the airport and stop the service at 0100 the following night once the last passengers have arrived. If required we could operate earlier or later depending on the requirements of the airport. We use the two hour shutdown to carry out maintenance and system improvements.

How many staff are needed to operate the system at Heathrow?
There are two shifts each day and there are three people on each shift. We have a controller who spends all their time in the control room, we have a technician who spends all of their time in the workshop and then a third staff member, a controller tech who is duel skilled and can work either as a technician or a controller. In our research into future applications of the system we can confidently say that a team of three people could easily operate a system that is at least double the size of Heathrow.

What is the profile of passengers that use the system?
The Business Car Park is marketed at customers with an average occupancy of 2-3 days so generally it is business travellers who are away for a couple of days at a time. We have however noticed that different types of travellers use the system at other times. We experience miniature peaks at weekends where leisure travellers on weekend breaks park their car. Further still, during school holiday periods we have found that parents are parking in the business car parks, we imagine partly for the convenience but we believe primary because experientially the technology is exciting and is a fun way to start a holiday. We are also often visited by groups and individuals who are not actually travelling but are interested in the technology.

Heathrow pod control interface

Have the passengers reacted to the system in the way Ultra imagined?
As this was Ultra’s first system we had very open expectations about how passengers would respond to the system. In many ways they have met our expectations; the intuitive nature of the system has meant that passengers have had no trouble using the system and any issues are responded to immediately by our staff in the control room. With quite a regular customer set we have noticed the development of an unique personal rapid transit etiquette, passengers will often invite others to share pods or simply ask if they can ask to share themselves. Having monitored social media over the course of the last few years we have had a real insight into the thinking of our passengers. We are delighted to see that passengers not only appreciate the experience of using the pods but that it is delivering a positive, tangible difference in terms of the quality of service provided by the airport.

What is the biggest challenge you have faced since opening?
One of the biggest challenges is that the introduction of the PRT system in May 2011 raised the expectations of passengers hugely. Passengers who were used to waiting 10 minutes for a shuttle bus now have an average waiting time of 10-15 seconds with 80% of passenger having no wait at all. Not every passenger who rides the system will have a pod immediately available to them and it is up to us to ensure that the minority of those who have a short wait are kept informed of when the next pod will be available. We have worked hard on ensuring the processes are in place to make sure that passengers are well informed and experience the best service possible.

How will you ensure that the service continues to provide a reliable service in the future?
As a company we are dedicated to the continuous improvement of the service at Heathrow. As part of this, and in response to our experience thus far, there have been a number of improvements to the system – both in terms of software and hardware. Some examples to highlight include big improvements to how we respond to snow and ice, our designated Ice Management Vehicle was largely rebuilt during the summer of 2013. Likewise we are now on our 6th release of our software ,which includes automated recovery of the system in any instances. All of this has enabled us to provide a service that has averaged over 99% reliability over the past 32 months.

Heathrow pod station

How often are the vehicles maintained?
Part of the reason we have been able to operate with such a reliable service is that each of the vehicles are constantly feeding back diagnostic information to the control room. This includes measures such as state of charge, tyre pressure and payload – to name but a few; consequently we are able to detect and diagnose issues often before they even occur, limiting the amount of time needed to maintain the vehicles. In addition to this, all vehicles are routinely checked on a daily/weekly/monthly/six monthly and yearly basis with checks varying from visual inspections to full MOT style examinations where the vehicles are taken apart.

Can we expect any other developments at Heathrow in the next 12 months?
In the very near future we are expecting to carry our 1 millionth passenger which is a huge landmark for us and the ATN/PRT industry in general. We continue to develop the system at Heathrow – new software releases are expected in the near future and upgrades to some of the queuing lanes within the business car park which, like those at Terminal 5, will be kitted out with chargers. We are also expecting the airport to expand the Business Car Park at Terminal 5. Often on a Tuesday/Wednesday the car park reaches its 1300 space capacity, therefore the airport is looking to deck the car park and expand capacity by several hundred spaces. We are pleased with this as it proves that passengers are clearly delighted by the service provided to them.


BlogIT-002: On Headway Discussions

There is nothing magical about PRT headways. The headway is the time interval between two successive vehicle noses passing by an observer who is standing beside the PRT guideway. The headway is important though, as the maximum vehicle flow (or the carrying capacity) is inversely proportional to the minimum achievable headway. What inspired people’s fantasy is that PRT’s automatically controlled vehicles could reduce headways significantly with respect to human driven cars and trains, thus boosting carrying capacity of PRT lines to a point where urban congestion problems would magically disappear, while maintaining the individual service qualities of private automobiles. This is indeed an intriguing thought, in particular when headways are close to zero seconds: while a headway reduction from 6 seconds to 3 seconds increases capacity from 600 to 1200 veh/h, a headway reduction from 1 second to 0.5 seconds ( just half a second!) would increase capacity from 3600 to 7200 veh/h.  The latter corresponds to the capacity of a freeway with 3 lanes per direction or an urban road with approximately 6 lanes per direction—a large road that could be replaced by a PRT guideway of only 1.6 to 2m width. This is why short headways have been termed as the “holy grail of PRT” and there have been endless debates on Internet sites and mailing lists on if and how PRT can achieve such short headways. The short headway discussion has even historical roots as all early, usually state financed PRT projects, aimed at developing PRT with mass transport capabilities.  This is probably why many critics have put forward extreme demand scenarios, like football stadiums or the lunch break at huge office building, claiming that these would be show-stopper applications for PRT.


But does PRT really need very short headways in order to find useful applications? The reality is that most urban areas are served by bus lines with modest carrying capacities (an urban bus with 75 passengers each 3 minutes transports 1500 passengers per hour). A PRT system with a headway of 3 seconds and an average vehicle occupancy of 1.5 to 2.5 passengers could match such capacities, while offering a comfortable non-stop ride, higher average speeds and guaranteed arrival times.  A two-lane, urban road with  traffic lights every 500m has similar capacities. Connecting car parking into city centers is an important application that requires even lower capacities. Thus PRT is more likely to compete with the road system with medium transport capacities, rather than with high capacity metro lines.

It is always important to remember that, in contrast with conventional transit, PRT  does not require  high concentrations of people – there is no need for PRT lines to intersect at central places where passengers can transfer. Nor does PRT create high demand surges by itself as each unit has 6 passengers maximum and vehicle arrivals are rather continuous. As PRT lines cost a fraction of light rail, one would build more guideways to cover an area instead of concentrating all the demand on a few lines.  It is often argued that capacity problems may occur where PRT is used as a feeder for conventional rail stations. This is true for big metropolitan stations,  but simulation studies clearly demonstrated that  short-term demand surges caused by an arrival of a single train (or airplane) can be handled by PRT if  stations and empty vehicle depots are located at strategic places.

Nevertheless, it is also true that PRT with even shorter headways and higher capacities could conquer a larger market.  But why has no PRT with sub-second headways made it to the market? A repeatedly asked question, nourished by the fact that several sub-second headway systems have already been demonstrated to work? For example Cabin Taxi in the late 70s or the platoon of  automated cars tested during the Californian PATH project in 1997.  Surely there are many technical details to analyze, but the main problem with short headway controls has been to quantify the probability of a fatal system failure, or likewise, the mean time between unsafe failures. This probability is necessary to certify the system for public operation as well as to assess the risk and potential insurance costs involved. The mean time between unsafe failures can be extremely long, as PRT must be at least as safe as the systems it replaces or competes with. For example, a micro-processor system for vital rail applications (which consists of several redundant processor units) has a time between failure in the order of 10hours or some 114,000 years. The efforts necessary to determine the mean time between unsafe failures have been regularly underestimated. It is not sufficient to run vehicles on a demonstrator for 500,000km  or more – instead, the probability of all vital components must be known (or tested) and the consequences of their individual and combined failures must be assessed. Also software must be proven to be error proof for all possible inputs, which is challenging with increasing complexity.

Now the PRT developer has basically two options: to develop a PRT specific control systems from scratch or to assemble a control system from already safety certified components and software.  As the first option is extremely costly, current PRT manufacturers preferred to buy in all or most of the vital components. However, this choice does also limit the ability to reduce headways below certain limits, because currently available vehicle control systems have  been designed for rail systems and more recently for cyber-cars, but certainly not for PRT with very short headways in mind. This is an important fact to acknowledge, as there have been misleading discussions on what are the available “off-the-shelf” components. The state of the art in train control (Automated Train Protection, ATP) does practically not allow headways much shorter than 3s. But any progress made in control systems for trains and the automobile sector could be beneficial for PRT too.

So what conclusions can be drawn? First, short headways are important but there are many transport applications where current PRT can be employed – linking car parking, feeders for public transport hubs, airport shuttles etc. Not being able to provide sub second headways is not a show-stopper for PRT.

Second, the PRT industry is very young and relies on sub-components from control systems of already established transport systems. PRT has taken a rather normal path of transport system evolution: the first railways did not connect major cities, the first airplanes did not cross the Atlantic, and the first rockets did not orbit the earth. But each system created a need to develop specialized key components: the superheated steam engine, the light weight combustion engine (followed by the jet engine) and the predictive flight controller finally allowed the respective transport system to conquer their potential market. It remains to be seen how fast a component supply industry  for PRT will develop. But in the short term, PRT will serve the many markets where it is currently most competitive.


BlogIT-001: Movers and Shakers

The advanced transit industry has been in development for a long time. With the first advanced transit system being realised at West Virginia University in 1975. From this point the industry slowly started to grow. New concepts such as Cabinentaxi and PRT 2000were pioneered but never fully matured, due to their development becoming rather more expensive than expected. The vehicles became larger and heavier than intended and/or the system transforming into an APM concept.It is only by the late 90s that the industry regained some momentum. With the introduction of a next generation of group transit systems at Schiphol airport and Rivium Business Park in the Netherlands which were followed shortly by the Bristol PRT test track. The latter, in particular, raised awareness of PRT and sparked an interest in the concept – both from proponents and skeptics.

Ultra Global PRT Cardiff Test Facility

Today there are two operational PRT applications: at Masdar City (Abu Dhabi) and at Heathrow (United Kingdom) plus, of course, the original Morgantown application. A third application is moving rapidly towards its official opening at Suncheon (South Korea). These first PRT applications are the start of the accelerated growth of the industry.

With all the fuss about it, for those working in the industry, it is sometimes difficult to forget that the concept is still widely unknown. Those that have heard of PRT, have heard it all: they know the history, the details, the possibilities and the claims that are being made. They represent the famous 80/20 rule: only 20% of the people is familiar with PRT, while 80% still is unaware of the concept and the capabilities.

At this stage of the development of the industry no aspect is standardised, making it difficult for anybody not working for a developer to know all the ins-and-outs and possibilities of each concept. There is no one-size-fits-all system. There are no rules-of-thumb. So how can a consultant gain enough knowledge to be able to properly advise his customers? How can customers obtain sufficient knowledge and an independent assessment about whether advanced transit is a viable solution for their transport issue?In fact there is such a diversity in technical solutions and characteristics, that the term PRT is being used for different type of systems (high speed vs. low speed, 2 passengers vs. up to 8 passengers, short distance – as a feeder – vs. long distance) which aren’t even alternatives to each other. One of the conclusions of the recent San Jose study was that the landscape of advanced transit is not easy to comprehend with the myriad of systems available.

With the term PRT perhaps not covering the load, new vocabulary has been introduced: ranging from Pod(cars) to Automated Transit Network and CyberCars. Adding to the confusion is how the systems relate to what people already know. Is PRT or Podcars a subset of APMs (Automated People Movers)? Do they relate to the Google cars?

VECTUS Suncheon Bay Project, South Korea

This is further complicated by a heated pro-con debate. PRT evokes a love or hate relationship. With the much of the discussion taking place online, all views and opinions are available at once to those new to PRT. This first contact can seem overwhelming; PRT is either the holy grail of transportation or the biggest scam in the history of transportation. It is, as you might expect, neither.

Where is this leading? It leads to ATRA. For years ATRA has been an organisation driven by dedicated individuals believing in advanced transit and what it could contribute to society. Now ATRA is transforming into a branch organisation providing a platform for discussions on advanced transit. Its website providing unbiased and relevant information on the current capabilities. The Industry Group within ATRA has been set up with the aim to unite industry participants, whether vendors,  consultants or academics. ATRA IG strives to educate the market on the possibilities, restrictions, limitations, opportunities and characteristics of the available systems. ATRA should be a guiding force in providing knowledge, distribution, research and consultancy.

In the end it is a task for ATRA, and all those contributing to it, to create clarity. Clarity for those interested in the advanced transit. Clarity in vocabulary. Clarity in the capabilities and restrictions. Clarity on what is proven, what is in development and what is a concept. Clarity amongst the different concepts.

The industry is continuing to mature and ATRA and ATRA IG are here to drive the process.