Considerations for Planning and Implementing FRT and PRT Systems in Carbon Neutral Environments, APS-ATS 2011, Menichetti Van Vuren

8/6/2019 Considerations for Planning and Implementing FRT and PRT Systems in Carbon Neutral Environments, APS-ATS 201

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Menichetti, Van Vuren

APM-ATS, 13th

International Conference, Paris, France, May 22-26, 2011

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Considerations for planning and implementing FRT and PRT

systems in carbon neutral environments

D. Menichetti1

and T. van Vuren2

1Mott MacDonald, now with Union Railway, Makeen Tower (Ajman Bank Bldg.) -

10th floor, Tourist Club Area, P.O. Box 989, Abu Dhabi, U.A.E.; +971 (0)

5044373412Mott MacDonald, Canterbury House, 85 Newhall Street; Birmingham, B3 1LZ,

United Kingdom; +44 (0)121 2374004; email: [email protected]

ABSTRACT

Masdar City in Abu Dhabi is currently under construction aiming to become the

worlds most sustainable development embodying the ultimate vision of a carbon

neutral urban environment. An important consideration in carbon-neutrality is the

organisation and provision of a transport system that does not rely on the internal

combustion engine, integrating active modes such as walking with electric transit

modes that combine capacity and penetration requirements.

Gaining from practical experience in Masdar City, the aim of this paper is to enhance

the understanding of transport planning challenges of implementing Freight Rapid

Transit (FRT) and Personal Rapid Transit (PRT) as key elements in an overall urbantransport system. Whereas current implementations have been short stretches of

individual line, in Masdar City an integrated MRT, LRT and PRT/FRT system will

aim to deliver a zero-carbon travel environment.

Key considerations are the reliance on FRT/PRT (and not on private vehicles),

system constraints, issues related to specific transport demand segments (e.g.

disabled, children, etc.) and travel purposes, interactions with the environment

surrounding the carbon neutral city, community characteristics, changes in behaviour

involved, and challenges for goods movements and deliveries.

We also discuss supporting measures for a successful FRT/PRT system, basically

creating the right environment for such systems to operate, referring back to theircontribution to Masdar Citys aim of carbon neutrality.


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1.INTRODUCTION

Masdar City in Abu Dhabi (see Figure 1) is currently under construction aiming to

become the worlds most sustainable development embodying the ultimate vision of

a carbon neutral urban environment.

Figure 1. Masdar City (source: Abu Dhabi Future Energy Company (Masdar))

A carbon neutral city is powered exclusively by renewable energy sources where

emissions of greenhouse gases within the city should be reduced to zero. Fossil

fuelled vehicles, typified by pipeline emissions, would not be employed within the

carbon neutral perimeter where the streets are narrow by design, well shaded and

dominated by pedestrians and cyclists.

Delivering a well-functioning transport system in a built environment typified bythese constraints but also recognising and catering for the transport requirements of a

modern city centre, challenges the transport planning discipline (see Figure 2)

How to plan a system able to satisfy the requirements of movingpassengers, freight and waste without the use of private vehicles with the

minimum impact on inhabitants well-being?


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How to provide car-like travel (on-demand, private, continuous,seamless, highly accessible, door-to-door or almost) and freight

deliveries, with equal flexibility, performance, comfort and level of

service?

Which transport system components would be suitable for suchapplication and how to integrate these with an external car-basedenvironment?

Figure 2. The transport planning challenge

As possible replacements for car and van-based services, there are expectations of

Personal Rapid Transit (PRT) and Freight Rapid Transit (FRT). PRT is an

innovative sustainable and green transport mode where passengers travel in small,

fully automated and individually controlled vehicles (or pods). FRT systems use the

same concept and basic infrastructure with vehicles adapted to transport freight. The

features of this system make it attractive for existing cities (HAMMERSLEY J.,LOWSON M.andKOREN N.,2010)as a potential replacement of fossil fuelled cars and

an excellent candidate for being integrated up-front as a key component in the

transport system of a carbon neutral city.

Gaining from practical experience in Masdar City, the aim of this paper is to enhance

the understanding of transport planning challenges of implementing Personal Rapid

Transit (PRT) and Freight Rapid Transit (FRT) as key elements in an overall urban

transport system, with wider lessons to learn for any application.

2.PERSONAL RAPID TRANSIT (PRT)

PRT is a safe, sustainable, green, innovative transport mode characterised by small,

lightweight, driverless, automatically controlled vehicles (seating 2 to 6 passengers)

operating between off-line stations in a network of interconnected, small, and

exclusive guide-ways (see Figure 3).

+ =

Peacefulnessof an old village

All the activities of amodern city centre

Carbon neutral

21st century city

?


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Figure 3. The Masdar City PRT

(Courtesy of 2getthere)

Guide-ways can be elevated, at grade or in tunnels as long as they are safely

segregated from other traffic and pedestrians. Flexible switching along the guide-

ways allows PRT systems to operate as networks, rather than a collection of

independent lines.

The use of off-line stations (see Figure 4), permits a high throughput of vehicles

allowing short waiting times in comfortable conditions.

Figure 4. K-13 PRT Station at Masdar City



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The infrastructure has the advantage that both guide-ways and stations can be easily

integrated with buildings reducing access/egress times and visual intrusion. From a

service point of view, PRT offers the potential of a high frequency, 24/7, congestion

free, on demand (taxi-like) service with direct origin-destination connections basedon a dense pattern of stations close to activities. In addition, PRT offers levels of

privacy to the travellers that other public transport system cannot match.

The concept of PRT is not new and its feasibility has been extensively studied since

the 1970s. Despite its environmental sustainability and promising performance

features, the financial and economic cases which have been made for individual

implementations and the positive responses of interviewed passengers, PRT has

never taken off. There are a number of reasons, among which the lack of adequate

control software/hardware, the competition from and continued efficiency

improvements in cars and traditional public transport modes, the reluctance of many

decision makers to implement an untested system and the uncertainties around the

social acceptance of a wholly new and unproven way of travelling.

However, during 2010 progress has been made with the first examples of small PRT

systems for public operation (excluding the Morgantown automated tram which

opened in the 1970s and is still in operation) at Heathrow airport and at MIST 1A in

Masdar City (which represents the first pilot PRT element aiming to set the scene for

future extensions of the system to other phases of the city). Nevertheless, we still

lack an application of PRT in public service within more complex urban contexts

competing with alternative transport modes, so that the passenger responses to such a

system are still largely unknown.

3.FREIGHT RAPID TRANSIT (FRT)

Freight Rapid Transit (FRT) has the same infrastructure and system control

characteristics of a PRT system but operates with vehicles modified to allow the

transport of goods or waste (see Figure 5).

As an example, the FRT vehicles in operation at MIST 1A at Masdar City are flatbed

vehicles with a loading deck. The size of the deck is around 3860 mm x 1420 mm

and when empty the loading surface is around 800 mm from the ground. The flatbed

FRT vehiclesare capable of transporting pallets or containers, but not loose freight.

The maximum (external) size of a container is of 3600 x 1400 x 2000 mm for an

internal capacity of about 9.5 m

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; the weight transport capacity of an FRT is 1500 kgwhich account for a payload of about 1200 kg assuming a weight of 300 kg for a

steel container. Containers can be specialized for different types of freight and waste.


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Figure 5. The Masdar FRT


4.THE CASE FOR PRT AND FRT SYSTEMS IN A CARBON NEUTRAL CITY

To provide a valid alternative to private cars, a transit system should deliver a

comparable quality of service and flexibility, ideally at lower costs (consideringownership and use). A system with the characteristics of PRT combined with the

software and hardware technologies of today could theoretically achieve this goal

making it an excellent candidate as a key component for the transport system of

carbon neutral environments such as Masdar City:

It is electric and non-polluting (if powered from renewable sources) It is more energyefficient than man-driven systems It is safer and requires less room than man-driven systems It requires less operational manpower than man-driven systems It is congestion free It is iconic and innovative It offers a better level of service than public transport It is more socially acceptable than public transport as a substitute for cars

Adding the benefits of FRT, which provides a distribution platform that utilises the

investment in PRT infrastructure, strengthens the case.


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5.TRANSPORT CHALLENGES FOR PRT AND FRT SYSTEMS

Because of the absence of a real life system in operation in an urban environment, we

have no alternative but to develop a simulation approach to identify and design out

any problems related to the reliance on PRT as a substitute for the private car beforeimplementation. This approach has been taken in Masdar City. Gaining from this

experience, the following sections present a list of practical issues to bear in mind

when planning and implementing PRT and FRT systems elsewhere.

The list is not comprehensive but covers what we consider to be the most pressing

issues and has the general aim to enhance the understanding and awareness of

transport planning issues when designing PRT or FRT systems aiming to replace

conventional fossil fuelled road vehicles for passenger and freight movements.

5.1 Passenger experience and social acceptance

Until a PRT system will be operating in an urban environment an important unknownfor the potential application is their acceptance by the public. PRT can be interpreted

as a modern version of the taxi, offering the further advantage of not having to share

the cabin with an unfamiliar driver, and the drawback that it does not always take

you exactly to your destination but to a station which will be a certain distance away

(although less so than for conventional transit systems). However, we would not

expect PRT to be valued the same as a car there are many other aspects of owning

and using a car that a PRT cannot emulate.

Nevertheless, in an environment where there is no competition with private cars, like

Masdar City, the PRT could make its role as a substitute more acceptable and it

certainly would require (from a passengers perspective) fewer compromises than

any other public transport or transit solution. As with any public transport system,

specific local requirements (e.g. the social stratification and separation of the sexes in

the UAE) may require adaptations of the system that are unnecessary in other regions

such as Europe or USA, where most of the PRT studies have been undertaken in the

past. These solutions are already adopted for taxis and can be transferred to PRT, for

example different types of vehicles for different social classes, separate boarding

berths at stations etc.

It is important to remember that these solutions have the drawback of reducing the

efficiency of the system (more vehicles, longer wait time, higher frequency of empty

runs, larger stations etc.) so their advantages must be carefully weighted against the

disadvantages. Asimulation approach will be able to support this.

Stated preference surveys carried out in Europe (COOK C., 2004) and the USA by

PRT vendors have shown, in general, very positive reactions from respondents to the

PRT system. However, these surveys were always carried out on scenarios where

PRT was providing a service from origin to destination with no transfers to other

means of transport. In Masdar City an important consideration is that the PRT


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system would be able to provide a point to point service only for trips wholly within

the carbon neutral city while those trips with origins inside and destinations

anywhere outside the City, for example in Abu Dhabi (or vice versa), would require

at least a transfer from PRT to a mass transit system or to private cars.

The transfer disutility, although acceptable for commuting, may be more of a

problem for typical off peak trip purposes such as shopping or in specific situations,

such as for example:

When taking the family out (eg. transferring children from a vehicle toanother, etc.)

For education trips (eg. for children living in Masdar City and studyingoutside, as compared to a school bus)

For specific transport demand segments (e.g. disabled, elderly people, etc.) bywhom transferring is perceived as a greater obstacle

We can conceive a situation where people may be willing to abandon the car forinternal trips where the PRT offers a car-like service but might continue to strive for

car ownership and use for trips with destinations outside the city.

Other important factors which could jeopardise the PRT passenger experience and its

social acceptance include:

The average and maximum walking distances from PRT stations Added delays because of stairs or elevators when the PRT operates on

elevated tracks or in tunnels

Levels of crowding at stations General station comfort Ease of use and reliability

5.2 Reliance on PRT and FRT

The implementation of PRT and FRT systems as a key component in an urban

environment is a world first. This exposes the system as a whole to risk, especially in

the early implementation stages. The reliance on PRT carries risk for a number of

reasons including, but not to be limited to:

Capacity might not be adequate PRT vehicles can break down, affecting reliability

Communication between vehicles and system control may fail Battery operated vehicles may not be able to cope with extended peak hour

traffic

An early accident or failure may cause over reaction and even potentialclosure of the system

The system is not socially accepted and therefore underused Liability and insurance issues


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In a city, where the transport system heavily relies on PRT, the consequences could

be potentially disastrous and it is of paramount importance to carefully mitigate each

of the risks.

Finally, PRT, even as a system, does not operate in isolation. Its success depends on

a successful implementation and integration with other elements of the transport

system. In Masdar City, for example, this means the external public transport

infrastructure (Metro and LRT) and the external car parks. It is desirable to plan the

development so that its full reliance on PRT is gradual, and able to cope with any

delay in the delivery of the transport infrastructure outside the city.

5.3 PRT capacity vs demand

PRT is not a high capacity means of transport. Simulations demonstrate that it

performs best when trips are distributed over time and space. It is less suitable for

asymmetric and peak demand, traffic concentrated in corridors and remotely locatedstations. For travel demand with these characteristics, conventional mass transit

systems (e.g. bus, LRT and automated people movers) would offer a better

performance. The systems are complementary.

It is of great importance to understand and evaluate the capacity limits against the

demand patterns during the evaluation and planning phases. However, PRT capacity

analysis is not as simple as for conventional public transport as it depends on many

interacting parameters, such as line-speed, line-frequency, vehicle protection

systems, station layouts, station operation, boarding behaviour, safety rules and

empty vehicle management (SCHWEIZER J.,DANESI A.,MANTECCHINI L., TRAVERSI

E.andCAPRARA A.,2010). As a result, the total PRT system capacity cannot be

determined by an individual analysis of each element but only when the system is

comprehensively assessed as a whole (e.g. the capacity of linear infrastructure

elements depends on the capacity of stations and can only be increased to certain

limits dictated by the maximum station throughputs, etc.).

Emerging PRT microsimulators can provide a robust assessment of capacity but they

are time and resource intensive which is prohibitive during early evaluation or

planning phases. However, recent advances in static tools for preliminary design

have lighter implementation (data) requirements and can be used to provide

preliminary and quick vehicle patronage and system and performance predictions

(DANESI A.,SCHWEIZER J.,TRAVERSI E. and CAPRARA A., 2009).

Nevertheless, any assessment of capacity cannot be considered comprehensive

without an evaluation against demand. The determination of overall travel demand,

its characteristics and spatial and temporal patterns is crucial for the assessment of

PRT system capacity and cannot be avoided.


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5.4 Demand estimation

In existing urban environments travel demand can be observed through surveys, on

street or within households or places of work. In newly developed cities such as

Masdar City demand must be synthesised, using relationships observed elsewhere,plus complex modelling approaches embedded in commercial software packages.

In Masdar City, Mott MacDonald developed a demand model (Figure 6) by adapting

available modelling tools and integrating them with innovative methods focused on

system specifics (MENICHETTI D.andVAN VUREN T., 2010).

Figure 6. Sample output from the Masdar City demand model

Specifically, this transport demand study provided support to:

locate potential critical system bottlenecks or local underperformance anddesign them out

identify where specific segments of demand requires additional serviceswhich the public transport system might not be able to accommodate

design a transport system with features suitable for the expected demand


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However, the estimation of demand for a carbon neutral transport system including

PRT remains challenging (ANDREASSON I., 2010) because of:

the impossibility to extrapolate or observe travel behaviour, demand patterns,passenger responses in the existing situations

the paucity in tested modelling tools to cope with the specific PRT systemrequirements

the need to represent transfers between PRT and other modes (including otherpublic transport, walking, cycling and cars)

the importance overall of external travel demand compared to moreconventional cities

The latter point will be discussed next.

5.5 Interaction with the surrounding environment

When planning a carbon neutral development and its transportation system, inaddition to the design requirements for the transport system within the city, the

interface with and impacts on the external transport system also needs to be

evaluated. A carbon neutral city needs to be accessible from the external world

which still relies on conventional vehicles. When using these modes to access/egress

the city, a transfer to the internal green modes is generally necessary to reach the

final internal destination and transfer facilities (car parking, pick up/drop off points,

stations etc.) need to be considered more carefully, as part of the integrated system.

Observed situations in conventional environments have taught us that walking and

transfers in general are perceived as major components of discomfort of a journey

and therefore car parks and public transport interchanges need to be considered as

critical points of the overall system and their design accurately assessed from a

passenger experience point of view, including any additional travel times incurred at

these locations.

5.6 Traffic impact of the development on the surrounding road network

A carbon neutral development should ideally not just avoid car usage within its

perimeter but also aim at reductions in car dependency in its surroundings.

Minimising the impacts of external (road) traffic and of intrusiveness of road

infrastructure and car parking facilities during each phase of the development

implementation contribute to the success of a carbon neutral city. Conventional

vehicular traffic expected to be generated consists mainly of:

private cars from and to the car parks, and vehicles transporting freight to be transferred from and to FRT at logistic

points and intermodal stations


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Although this traffic can be reduced, it cannot be avoided and needs to be managed

in order to reduce its impacts. Typical management measures could include car park

allocation and information, car park pricing, dedicated routes for heavy vehicles etc.

Low emission vehicles could be promoted through pricing measures.

5.7 Freight movements and deliveries

A service able to reach every building of a city with deliveries and the collection of

freight and waste is fundamental in any urban environment. In Masdar City, the

specific urban architecture typified by narrow roads where the access of conventional

freight vehicles is neither desirable nor always possible, requires tailored solutions.

An FRT system can be employed for freight and waste in combination with logistics

points and intermodal stations located in the vicinity of the city.

However, this system presents a number of challenges to be addressed. One of the

biggest is represented by the capacity limitations of individual FRT vehicles which

can only handle small to medium size goods but cannot cater for big size deliveries.Another issue is that like PRT, FRT vehicles move goods from a station to another,

hence they cannot perform a door to door delivery service and the final journey leg

(from the station to the final destination) needs to be handled by a different means of

transport. Finally, if the FRT stations are in a tunnel or elevated, goods will need to

be transferred using a system able to operate between the different city layers.

Hazardous goods pose an additional problem.

5.8 Integration between FRT and PRT

FRT vehicles can operate on dedicated infrastructure or share it with PRT vehicles.

When sharing the same PRT infrastructure, the FRT vehicle cannot exceed the

dimensions of a PRT vehicle. On the other hand, building separate FRT

infrastructure would imply extra cost but could allow the use of bigger vehicles along

with reduced capacity constraints. Such a dual system might also provide an

alternative should one of the components fail completely.

Nevertheless, to reduce costs and maximise efficiency, it seems reasonable to operate

FRT vehicles in circulation on a single shared network with PRT. In this scenario,

the only drawback is that the FRT vehicles in circulation may reduce the PRT

capacity. This can be minimised by careful scheduling of freight and waste activities

in the off-peak periods.

5.9 Integration with other transport modes

PRT systems are heavily automated and must be segregated from any other traffic,

pedestrians or animals and cannot be crossed in any way during operations. This

makes solutions at ground level difficult as grade separated infrastructure would need

to be provided at every crossing point.


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This limitation makes PRT in elevation or in a tunnel typically the preferred solution

with the advantage of ease of network design but with the disadvantage of creating a

basically continuous multi-layered transport system across the city, with vertical

obstacles part of most journeys (see Figure 7).

Figure 7. The multi-layered transport concept of Masdar City

(source 2009, Abu Dhabi Future Energy Company (Masdar) PJSC/Foster+Partners)

6.WIDER CONSIDERATIONS FOR A SUCCESSFUL PRT/FRT SYSTEM

When planning a transport system for a carbon neutral city, there are two questionsthat need to be answered:

is there enough capacity in the internal transport systems to cope with thedemand?, and

is there enough capacity in the external transport systems to cope withdemand?


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To answer these questions (and as discussed earlier), it is necessary to employ

modelling techniques to predict the travel demand and compare it with the transport

capacity for each mode of travel. This analysis needs to be undertaken not only for

the full built out scenario but also at other relevant points in time during itsimplementation (e.g. at the end of each development phase). If PRT does not have

sufficient capacity, then either demand must be reduced, or extra capacity must be

provided. Without one or both of these measures there will be delays and queuing.

In the following sections we discuss what we consider are important considerations

and supporting measures for a successful PRT and FRT system, basically creating

the right environment for the successful performance of such systems, contributing to

Masdar Citys aim of carbon neutrality.

6.1 Ensure balanced land-use and promote self containment

Demand analysis undertaken in Masdar City for city wide future PRT scenariosshowed that PRT would be approaching its capacity during peak hours. This effect

was driven mainly by large passenger demand flows concentrated in limited time

periods and in a limited number of corridors. The main cause was an unbalanced land

use distribution: the number of workers in Masdar City was far higher than the

planned resident population. This resulted in a large number of workers commuting

to and from Masdar City from outside locations and, in turn, placed a large and

imbalanced demand on the internal transport system and especially on some

interchanges to PRT remotely located near the city perimeter and on few corridors

connecting these stations to the city centre where most of the commercial activities

are planned.

As discussed earlier, PRT systems underperform with asymmetric demands, high

demand peaks and remote station locations. By implementing measures to reduce the

severity of each of these three factors, the PRT performance and efficiency would

certainly increase.

A first measure to reduce external transport demand is to increase the residential

population within Masdar City. This would provide greater opportunity for people to

live and work within Masdar City, greatly reducing the number of external trips.

This would be at the cost of increasing the number of internal trips, but as these will

be carbon-neutral, and shorter than external trips, this should add to the sustainability

of Masdar City. A second measure to reduce travel to and from Masdar City would

be to reduce the overall employment to levels matching the working age population(although of course this would not reduce commuting to zero, due to skills

differences between the resident population and the available jobs). A third measure

would be to redistribute the land-use to reduce the distances between the most

important activities, hence reducing the need for using PRT and contemporarily

increasing walking and cycling (e.g. car parks and bus, taxi and school bus stops as

close as possible to key plots, etc.). A fourth measure would be to maximise the


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citys self-containment by implementing policies aiming to ensure that residents

actually work in Masdar City (company housing, balanced job type opportunities,

adequate number and type of schools for all pupils etc.)

6.2 Complementary measures to PRT systems

If complementary transport is needed to supplement PRT, then it would ideally be

some form of mass mover compatible with the largely pedestrian environment and

able to absorb part of the peak demands relieving PRT vehicular traffic movements

on specific corridors.

Providing such a complementary transport system has the added advantage of

allowing PRT implementation strategies to be staged with other, more established

means of transport. This will alleviate the risks related to social acceptance and

system reliance.

a) Increase walking

The simplest and possibly most cost-effective solution to reducing demand for PRT

is to encourage people to walk more. This may be by making it possible to walk

further, or it may be by reducing the distance walked, e.g. by locating car parks

nearer to destinations, and jobs and schools nearer to homes. The best way to reduce

walk trip lengths is to review the land use distributions.

b) Group Rapid Transit (GRT)

Because of the on demand operation and privacy aspects of the PRT system, most

PRT vehicles are expected to carry only one or two persons, even in the peak

periods. If occupancy could be increased this would increase system capacitysignificantly. In principle, four-seat PRT vehicles could carry up to six people, with

two standing.

To increase the occupancy of PRT vehicles, passengers could be pre-grouped before

getting in the vehicle, or station bays would need to be assigned to specific

destinations, like a bus station. People would then go to the bay serving their

destination, and only when a vehicle is full it would depart.

It would then travel directly to a destination and the control system would optimise

the order in which different stations were called at. Each passenger would still be

dropped at their chosen station. This would reduce the number of vehicles travelling

through the system, but would increase travel times and provide a slightly lower

quality of travel for commuters, as they might have to stop a few times before their

own destination is reached and share their vehicle. However, this solution can

increase the capacity substantially at the cost of a slight reduction in quality of

service during peak hours. This is not unreasonable and generally accepted in most

conurbations.


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Given the short average journey times on PRT this could provide extra capacity at

minimal extra cost. The extra cost would be for upgrading the control system and

stations to manage group travel.

A further enhancement might be to add higher capacity vehicles, taking say eight or

ten people, but this would increase the infrastructure cost of the system. Another

possible option to increase occupancy could be platooning some of the PRT vehicles

to form small trains again serving fixed routes, however with the disadvantage of

requiring different station arrangements and also losing some of the most distinctive

features of the PRT system.

c) Extension of Light Rail Transit (LRT)

Masdar City has currently a planned LRT route running diagonally through the citysquare with four stations along its route. In the longer term, the LRT network within

Masdar City could be extended to provide a denser coverage of the city. One way ofdoing this could be to add a second line, possibly as a loop.

LRT systems are powered by electricity and can penetrate the perimeter of carbonneutral cities. They work most efficiently with high demand along a long thincorridor and can effectively support the PRT system by absorbing the in-commutingdemand from outside the city to high volume attractors within. The disadvantages ofthese systems are the rather high costs and the requirement of larger right-of-ways.On the other hand, they present the advantage of sharing space with pedestrians.

d) Direct bus service penetrating the city

As previously discussed, most of the travellers arriving at Masdar City are expected

to transfer to PRT to complete their journey to their internal destinations. The rest

will be able to walk to their destination directly after leaving the external transport

mode. If PRT cannot cope with this demand, then an alternative form of transport is

needed. One solution would be for zero-emissions buses arriving at Masdar City to

enter and drop passengers within the city. They could also pick up car travellers who

have parked in the external car parks.

Electric buses are flexible and routes can be changed easily as the city continues todevelop. They are established technology, and zero-emission hydrogen fuel-cellpowered buses are available, although expensive at present. They are able to absorbcommuting peak demand, hence reducing the pressure on the PRT system. The useof electric buses could also be a good and flexible interim solution until the externalpublic transport system (ie. Metro, LRT) serving the city would become operational.

e) E-cars

There are two forms of e-cars:


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e-taxis, which are manually driven zero-emission taxis, and e-cars, which are automatically controlled in areas where the control system

is provided

The latter are very similar to PRT in that they can be called up and discarded at theend of the journey, and stored automatically in a parking space somewhere until

required. E-cars can be privately owned, or made available through a car club or car

hire system. The disadvantage of e-cars is that the system, with equal provision of

infrastructure, would have much less capacity compared to a PRT system and that e-

cars would contribute little to reducing PRT demand, as their main use would be for

trips outside the city. However, e-cars have the clear advantage of the opportunity to

be driven outside Masdar City with no transfers.

f) Scheduling freight deliveries

When sharing the same infrastructure, FRT vehicles contribute to congestion and

therefore reduce the system capacity of the PRT system for transporting passengers.However, typically, passenger demand is concentrated during specific peak hours. A

transport system designed to cater for the peak will have spare capacity available

during off peaks hours. While the PRT system needs to provide a 24/7 service on

demand, freight and waste deliveries/collections can be scheduled during specific

time bands avoiding this traffic during peak hours and therefore increasing the

system efficiency.

g) Complementing vehicles for special or big size freight deliveries

One of the main issues of FRT vehicles is the impossibility to perform big size

deliveries because of their capacity constraints. A possible solution would be to

provide physical corridors to allow bigger zero emission vehicles to penetrate thecity including electric buses. These dedicated routes could also be used by waste

collection vehicles and would also be able to accommodate emergency vehicles.

In a car free environment it is not desirable having big vehicles running around the

city. However, the circulation of these vehicles can be managed (e.g. circulation only

during night hours) minimising the impact on the Masdar City living environment.

Complementing the FRT system in this way would overcome the vehicles capacity

limitations and also reduce the risks related to the full reliance on the FRT system for

freight transport.

7.CONCLUSIONS

The challenge for a zero emission transport system for a carbon neutral city is to

deliver a well-functioning and socially accepted service in a built environment with

strong constraints but also recognising and catering for the transport requirements of

a modern and vibrant urban centre.


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Personal Rapid Transit (PRT) has system characteristics suitable for such an

application and, from a passengers prospective, is certainly a more acceptable

substitute to private (combustion engine powered) cars than conventional mass

public transport systems. Freight Rapid Transit (FRT), integrated with PRT, can beutilised for the waste and freight deliveries/collections within the city, using the same

infrastructure.

The implementation in Masdar City of these systems city-wide in an urban

environment is a first and there are uncertainties, for example the social acceptance

and the performances of PRT and FRT in a complex network, rather than a single

line. Reliance on PRT and FRT also encounters a number of possible physical

constraints. In the absence of existing real life systems in operation in urban

environments which could be used in planning, a simulation approach is required to

identify and design out any problems related to the role of PRT as a substitute for the

private car.

PRT capacity analysis against demand teaches that asymmetric demand concentrated

in peaks and over corridors, as well as remotely positioned stations have a

detrimental impact on system performances while the system performs more

efficiently with medium demands spread over space and over time. Trips with

origins within the city and destinations outside (and vice versa) require transfer to

other means of transport. The design and performance of transfer facilities plays a

fundamental role in efficiency and the way passengers experience PRT.

Creating an environment characterised by balanced land uses and high levels of self

containment in combination with the provision of complementary transport systems

relieving PRT from peak demands, and with policies and designs aiming to increase

walking and cycling, can substantially improve the performance of a PRT/FRT

system in a zero carbon environment. Simulation of the system in all its stages of

evolution, recognising the importance of interaction with the outside world, will

reduce the risks related to such an innovative system, hence contributing to the

success of a carbon neutral development, such as at Masdar City.

DISCLAIMER

The opinions expressed in this paper are those of the authors and do not necessarily

reflect the views of either Mott MacDonald, Union Railway or the Abu Dhabi Future

Energy Company (Masdar).


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