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MARTIN LOWSON FREngUNIVERSITY OF BRISTOL ANDADVANCED TRANSPORT SYSTEMSLTD

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Background

For many years it has been clearthat the world faces a majorproblem in urban transport.

Congestion in major cities has reducedtraffic speeds to a crawl.* Congestion isalso the principal cause of excessenergy use and emissions output by

transport. Over the years there has beenan extraordinarily large number ofanalyses of the problem. To date nosolution has been found.

It has been suggested that cities arethe engine of the economy, and thattransport is the oil for the engine. Thereis a need to consider the benefits ofchanging the oil.

Historical analysisBefore looking to the future it is wise tolook to the past. Figure 1 (presentedoriginally in Lowson, 1998) shows thedevelopment of surface transport in theUK over a quarter of a millennium, interms of the build rate, non-dimensionalised against the maximumfor each system.

Figure 1 shows that transport doeschange. In 50 years time it must beassumed that another surface transportsystem will be in place. It seemsprobable that this will make the samecontribution to the present century asthe car–road system made to the lastcentury and the rail system to thecentury before.

Some important clues to the likelycharacteristics of this new systemcome from further historical analysis.

Engineering theULTra System

* In Outer London, the most recent 1998

Journey Times Survey shows that overall

A–B speeds at peak are only 8.5 mile/h by

car and 5.0 mile/h by public transport . This

reduces to 3.0 mile/h by car and 3.5 mile/h

by public transport in Central London.

Although transport is anessential catalyst for humaninteraction, transporttechnologies remain rooted in aprevious era. Informationtechnology has fuelled thedevelopment of the knowledgesociety. ULTra provides anopportunity to catch up withthe demands of a society whichis computer literate buttransport moribund.

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Every previous change in surfacetransport has involved a change of bothvehicle and infrastructure. Thus it islogical to examine new systems whichfeature a change of both vehicle andinfrastructure. This has provided newopportunities unconstrained by thelimitations of existing systems.

The key technology for the train,Richard Trevithick’s high pressure boiler,was invented just after the major peak incanal building. But high pressure steamcould provide only marginal gain for thecanal system. Similarly the key inventionfor the car–road system, the internalcombustion engine, was invented justafter the second major peak in railwaybuilding. Again, the application of theinternal combustion engine to therailway provides only marginal gain oversteam. In both cases, it needed thedevelopment of a new transport system,vehicles and infrastructure, to exploit theopportunities offered by the newtechnology.

We are now past the major peak ofmotorway building, so, by analogy withthe past, it is reasonable to supposethat the key technologies that will drivethe next form of surface transportshould be available now. Indeed theseare almost certain to be moderncomputing and information

technologies. But again by analogy withthe past, it can be inferred thatapplication of these technologies toexisting transport systems will provideonly marginal gain. A new system isneeded to exploit the opportunitiesoffered by the new computingtechnologies.

This thinking provided the impetusfor the present work. There appeared to have been no fundamentalreassessment of the requirements ofurban travel and how best to meetthem. Urban transport was a problemwhich cried out for re-examinationusing modern systems engineeringprinciples.

Systems engineeringanalysis and synthesisThe objective of the systemsengineering approach was to identifythe ideal system for future urbantransport. A requirements analysis forurban transport suggested that theoptimum system should offer thefeatures shown in the box to the right.

This requirements specificationformed the basis for the synthesis of anurban transport system. The systemwhich emerged has been called ULTra,short for Urban Light Transport.

Available on demandULTra is an automatically controlled,personal taxi system of four-seatvehicles that run on their ownsegregated guideway network.Transport is available on demand at anyof a series of stations distributedaround the city like cab ranks. Theempty vehicle management systemensures that a vehicle is nearly alwaysavailable at the cab-rank as required.Simulations of the full application inCardiff at peak periods have shown thatnearly all passengers (>90%) wouldobtain immediate service from a waitingvehicle. Wait times in all applicationsstudied to date are comfortably withinthe design target of 90% of all tripdemands met within a minute.

Non stopAll stations are off-line, so there is noneed for vehicles to stop during theirjourney. As a result, although maximumspeed has been limited to 40 km/h(25 mile/h) to enhance safety, trip timesare still reduced by a factor of betweentwo and three compared to cars orbuses in a congested city centre, or tolight rail.

AccessibleULTra provides car levels of service tonon car owners, including the youngand the old. In the city centre, or underother congested conditions, thisprovides a far better transport service

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Figure 1: UK surface transport history

The optimum urban transportsystem should

● be available on demand

● go non-stop from start todestination

● be easily accessible and offer afull choice of destinations

● be environmentally sustainable

● have a low cost

● have demonstrably high safety,together with personal security

● integrate well with other formsof transport.

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than is available from the car, or anycurrent form of public transport. Asmart-card system permits any user torequest direct transport to any otherstation on the network.

The system provides significantlyincreased accessibility for those with awide range of disabilities. There is nochange in level between platform andvehicle floor and the vehicle door hasbeen designed to facilitate entry.Appropriate lifts are provided for highlevel stations. The vehicle design canaccommodate a wheelchair andcompanion, and wheelchairs can beturned around inside the vehicle.Following discussions with the mobilitygroup of the Department for Transport,special emphasis will be put onproviding a system which meets theneeds of the partially disabled (e.g.those who are partially sighted or havemovement difficulties).

These design considerations alsogreatly facilitate travel by everyonewhose mobility is temporarily restrictedby luggage, shopping or children inpushchairs.

Environmentally sustainableSustainability issues are critical for 21stcentury transport. Analysis, shown herein Figure 2, suggested that most formsof transport, public or private, havesimilar levels of energy use andemissions output. Because the ULTra

vehicle is electrically powered there iszero emission in the city, but, in anycase, overall energy and emissions aresignificantly reduced. The averagesystem energy usage is 0.55 MJ perpassenger km. This can be comparedwith figures between 1.2 and 2.4 MJper passenger km shown forconventional forms of transport inFigure 2. The typical benefit comparedwith cars is over 70%. Importantly, inpeak periods when cars (and buses)are restricted by congestion this benefitrises to nearly 90%.

This energy saving translates directlyinto reduced carbon dioxide emissions.The system meets the recommendationof the Royal Commission onEnvironmental Pollution, following theIntergovernmental Panel on ClimateChange, that the carbon dioxideemission should be reduced by at least60%. The RCEP target is set for 2050.ULTra is able to exceed this target inthe present decade.

Resource usage is also considerablyreduced because of the small scale ofthe system. Vehicles are reused manytimes during each day, so each 400 kgvehicle does the job of about forty1000 kg cars. Infrastructure costs, andresource usage are down by a factor ofbetween six and ten compared withroads or motorways.

Because the vehicles requireconsiderably lower power than other

forms of transport there is a significantreduction in noise. Initial measurementsduring vehicle drive-by at 6 m/s gavenoise levels which wereindistinguishable at 10 m against abackground noise of 35 dBA. Thiscompares with a car, which wouldmake about 65 dBA at the samedistance during drive-by.

Low costDesigns undertaken by Arup show thatinfrastructure construction costs for theoverhead guideway are less than for theequivalent footbridge, and for at-gradetrack less than the equivalent footpath.This is because the system loadings ataround 1500 N/m2 are less than thepedestrian crush loads required forfootway design, i.e. 5000 N/m2. Thisalso means that the system can be runinto buildings designed to existing floorloading codes with no structuralchange. Complete system cost alsoincludes other infrastructure such asstations, together with vehicles, controlsystems and support, such as ticketingand closed-circuit television (CCTV).These costs vary considerably withdetails of the application but typicalcosts for a complete system in a varietyof applications have been around £5Mper kilometre of guideway. In a varietyof applications studies it has beenfound that these costs are around one-third of the cost of a light rail systemdoing a similar task.

Safety and securitySafety is the prime design requirementfor any transport system. ULTra isdesigned to exceed the best safetystandards of modern public transport.The detailed concept safety paperdeveloped by Advanced TransportSystems Ltd has received a ‘Letter ofNo Objection’ from HM RailInspectorate. By providing an effectiveform of transport, which will encourageexisting car users to use safer publictransport, significant benefits can beprojected in terms of fatalities, andserious or slight injuries. For the Cardiffapplication, analysis of existing

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statistics suggests that the benefit ofthe system would be a saving ofaround 50 accidents a year.

ULTra offers significant benefits inpersonal security. All trips areundertaken only with companionschosen by the traveller. As notedabove, during peak periods 90% oftrips are available immediately ondemand. Off peak, this figure rises to100%, since vehicles can be assured tobe available at all stations. Thus, therisks associated with waiting for publictransport are almost eliminated. Further,all stations will be under continuouscoverage by CCTV, with direct links tothe controller available from all vehiclesand from all stations via help buttons. Inaddition, in-vehicle CCTV is an optionwhere required.

Integrated transportThe system is complementary toexisting forms of transport. By providinga network link, with on-demand access,to major bus and rail stations or topark-and-ride sites, it will improve theattractiveness of these modes. This cancontribute to improved transportation,both directly and by enhancing theappeal of other modes. A recent statedpreference study in Cardiff suggestedthat the proportion of people usingconventional public transport such asbus and rail would be doubled if therewere an ULTra distribution network atthe city end of the system.

Personal rapid transit ULTra is a form of transport genericallyknown as personal rapid transit, orPRT, and has been examined byothers. The first study to clearly outlinea system which is essentially PRT wasby Donn Fichter in the late 1950s. Anextensive study was undertaken in theUS at the Aerospace Corporation,starting in the 1960s, and considerabledetail is provided in the book by Irving(1978). The ideas were furtherdeveloped by Anderson (1977).

In the UK, a proposal put forward byBlake culminated in the Cabtrack

system which was extensively studiedin the late 1960s (Langdon (1971)). Theprincipal problems with Cabtrack werethe cost and visual intrusion of theinfrastructure, which was over 3 m indepth. Cabtrack also used multi-levelexchanges, which increasedsignificantly both the cost and visualintrusion of the exchanges. This wasexacerbated by the Cabtrack controlpolicy which required acceleration/waiting/deceleration lanes at everyjunction. Generally Cabtrack appears tohave concentrated on the vehicleissues, and given inadequate emphasisto the problems of the infrastructure,including stations. Compared toCabtrack, the present system hasidentified many areas for reduction ofcost and visual intrusion.

At that time there were also severalother studies. In addition to the USstudy mentioned, other systemsinclude Aramis in France, the subject ofa book by Latour (1996), CabinenTaxiin Germany, and CVS in Japan. Noneof these reached fruition. It isinteresting that many of these systemswent through the samemetamorphosis, moving from personalrapid transit to group rapid transit.Unfortunately any form of group rapidtransit brings with it the fundamentaldifficulties of collective travel, i.e.waiting and, because of the need forstops, the problem of either low speedor inadequate accessibility. Automatedgroup rapid transit with small vehiclesraises the further problem of a possibleenforced ride with undesirable travellingcompanions. This issue would be afundamental barrier to acceptancetoday.

The reason for this metamorphosiscan be traced to the selection of theincorrect application for the system.The present system can be highly

effective for travel over the whole ofmodest scale cities such as Bristol, orin the outer areas of very large citiessuch as London. The system ascurrently configured is not well matchedto the problems of the centres of thelargest cities, where conventionalsolutions such as an undergroundrailway are reasonably effective.Unfortunately Cabtrack, Aramis andAerospace took, respectively, London,Paris, and Los Angeles as theirprincipal target cities. This significantlydistorted the conclusions, and led tominitram type approaches, whichdiscard the key conceptual advantageof personal transport. With Aramis, thedesigners were always committed to acorridor system, and so excluded themajor transport advantages of anetwork approach from the start.

One system with many technicalfeatures in parallel with the presentideas is that at Morgantown in theUnited States. This has fully automaticcabs on a dedicated guideway. It hasbeen running successfully for 20 yearsand has now carried 50 millionpassengers without incident. Althoughcalled PRT, the cab capacity is 20, andit is in reality a collective-corridorsystem linking two parts of a universitycampus. Nevertheless, it doesdemonstrate that a fully automaticdemand responsive system can betechnically successful.

Generally it seems that PRT studiesundertaken in the 1960s and 70s wereideas which were ahead of their time.We have been able to make significantimprovements over these systems, andeliminate a number of the technicalweaknesses of old solutions, especiallyin the approach to infrastructure. Also,today we are able to exploit a widerange of new technologies, especiallycomputing.

any form of group rapid transit brings with it the fundamental difficulties of

collective travel

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The ULTra system VehiclesThe prototype ULTra vehicle isillustrated in Figure 3. It is based onconventional automotive technologies,and is electrically powered with fourconventional rubber wheels.

shown that it is practicable to rechargea 5 minute trip in 1 minute. Batterypack weight at 64 kg is only 8% ofgross weight, compared to manyelectric vehicles which require up to50% of gross weight for batteries. Thiscould make electric vehiclespracticable.

mentioned above, and the structuralcost and performance predictions havebeen confirmed in the build of theprototype system. Columns aredesigned to be truck proof.Considerable attention was given tominimising visual intrusion during thedesign. Thus, it was very pleasing tofind in questionnaire studies that over90% of people were very happy withthe appearance of the track and fewerthan 1% felt that it would be anunacceptable intrusion in their city.

ULTra vehicle:

Principal parameters

Gross weight 800 kg

Empty weight 400 kg

Maximum speed 40 km/h

Length 3.7 m

Width 1.45 m

Height 1.6 m

Passengers 4

Continuous power 2 kW

ULTra guideway

Principal parameters

Overhead or at-grade alternatives

Width 2 m

Overhead

Depth 0.45 m

Height above roadway 5.7 m

Column spacing 18 m

Principal parameters are given in thebox. The vehicle is equipped with twopermanent and two flip-down seats andhas a level entry from the station. Thus,there is plenty of room for wheelchairs,shopping or pushchairs (Figure 4).Doors are automatic and have a novelpatented opening action.

Because the vehicle is light andtravels only at low speed, powerrequirements are low. This means thatbattery power with opportunityrecharging is practicable. Tests have

Figure 3: Prototype vehicle

Figure 4: ULTra vehicleinterior

Questionnaire studies in Bristol andCardiff show that 98–99% ofrespondents believe the vehicle interiorand exterior to be good or excellent.This is very encouraging.

GuidewayThe track has been designed inconjunction with Arup. Details are givenin the box. The track is low cost, as

Network and control systemULTra runs on its own guidewaynetwork with off-line stations. Typically,the network is arranged in a series ofloops serving key transport locationsaround the city. These loops arecombined by merge/diverge sections.

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In combination with off-line stations thisprovides non-stop travel. Track ispassive, and switching is achieved byin-vehicle steering using an electronicguidance system. Stations havespacings similar to bus stops. Thenetwork form allows the guideway tobe one way, providing importantbenefits in cost and visual intrusion. Avariety of application studies has beencompleted and it is typically found that,to provide reasonable accessibility,individual tracks need to be spaced ataround 500 m separation, or aboutevery sixth side road.

Operation of the network is basedon a synchronous system with fixed‘slots’ for each vehicle at the prescribedheadways. This requires free routes tobe identified from start to destinationthrough all merges before launch of atrip from the station. Extensivesimulations have been done to optimisethe synchronous control process,including development of effectiveempty vehicle-management algorithms.It is found that around 65% of theavailable line capacity can be used.However, in nearly all applications thecritical factor on overall system capacityis found to be the stations rather thanthe line. Small multi-berth stationspermitting a throughput of up to 500vehicles per hour have been devised.

A mature headway of 1 second isplanned. This will permit meeting-brick-wall stop criteria. Early applications willhave a considerable margin over this forsafety reasons. The mature headwaypermits a typical passenger load duringthe peak hour of over 2000 passengersper route kilometre, assuming anaverage 1.4 passenger per vehicle load.This is a larger capacity than actuallydelivered by any UK light rail system, sothat ULTra has an effective mass transitcapability.

It is ironic that, although around 85%of all trips over 1 mile in the UK are infact done by small vehicles, i.e. cars,conventional wisdom is that effectivepublic transport must require somesuper-scale vehicle for ‘mass transit’.Except in the largest cities such asLondon, this view is false. Inmanufacturing, it is widely recognisedthat mass production should bereplaced by just-in-time methods. Thisrealisation has not yet reachedtransport. ULTra can be regarded as ajust-in-time transport system. A highlysimplified analysis is given below.

Current project position The ULTra system is currentlyundergoing prototype testing on twotracks: a simple track in Bristol and amore complex 1 km guideway withoverhead sections in Cardiff. Initialresults have been very encouraging.Vehicle and track have been successfullyintegrated and over 1000 circuits of thecomplex guideway have beencompleted under fully automatic control.

Figure 5 shows a recent picture ofthe ‘A’ and ‘B’ vehicles on the CardiffTest track. The new ‘B’ vehicle is fullyfitted out for passenger carrying, andincludes several developments. Anemergency hatch has been

incorporated in the windscreen. Fullyautomatic doors are included and theinterior has been lengthened by120 mm, following comments fromCardiff disabilities groups.

The National Assembly of Wales hasapproved a bid by Cardiff CountyCouncil which will allow the council tosupport the first stage in implementingULTra. This will enable the system to beoperated between the Bute Streetrailway station and the Inner Harbour,Wales Millennium Centre, NationalAssembly of Wales and County Hall.Progress on the link between the Bayand the city centre will be progressed inparallel, possibly as a public/privatepartnership project. It is envisaged thatvehicles could be operating in the Bayarea by early 2005, with the city centrebeing connected during 2005 if thepartnership approach is successful. Theestimated costs of the complete 7.7 kmscheme are £39M. Projected passengerlevels are five million per year.

Cardiff is particularly suited to theULTra system because regeneration hastotally changed the transportationrequirements. The docks area, a formerindustrial zone, is now a prestigiousbusiness and residential centre but onewhich is, at present, disconnected fromthe main city centre. Journeys betweenthe two centres are already causing avariety of difficulties. Analysis shows thatULTra offers an effective solution, bothdirectly and by complementing existingpublic transport. Based on the recentstated preference studies, the addition ofa network link in the Bay area would leadto 1 800 000 additional trips per year on

Simplified analysis of theoretical capacity

50 seat bus every 5 minutes provides 600 seats/hour

200 seat light rail every 10 minutes provides 1200 seats/hour

4 seat ULTra every 3 seconds provides 4800 seats/hour

Figure 5: ULTra vehicles on the Cardiff test track

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conventional rail and bus transportsupported by the ULTra network.

Other applicationsSubstantial interest has been expressedin the system worldwide. In-depthstudies, supported by the EC under theEDICT programme, have started onpotential applications in four Europeancities: Cardiff, Eindhoven, Stockholmand Rome. These will examine thepotential of the system in a variety ofdifferent European scenarios.

Considerable interest has also beenshown in the system for application notonly in cities, but also in:

● Airports: especially for ‘landside’applications serving the parking andrental car areas. In effect, ULTrabrings remote areas within minutesof the main terminal and thus offerssignificant commercial gain. Detailedstudies are in progress on anapplication to Heathrow.

● Institutions: for example industrial,commercial or academic campusesand also major visitor attractions.

● New developments: this is perhapsthe most exciting opportunity.Because of the intimate link betweenthe community and its transportinfrastructure, change to thetransport system brings with it theopportunity to examine new forms ofurban living, enabling space devotedto cars to be returned to use bypeople. A study is in progress on theopportunities offered by applicationto a new development in Corby.

ConclusionsMeeting the challenge of providingsustainable mobility will requireconsideration of innovative solutions.Existing forms of public transport aremismatched to the form of presentcities, which have been shaped by thecapabilities of the car. There is a needto examine public transport which canequal or better the convenience of thecar, but at considerably reducedenvironmental impact.

The ULTra system has beenconceived to meet this requirement. Itcan be regarded as an automaticpersonal taxi system, since it respondsto individual demands and passengersshare trips only with chosencompanions. This makes it uniquelyattractive as a public transport system.Because the system retains many of thequalities of car-based transport – privacy,immediate access, non-stop travel – itcan appeal to users who are unwilling orunable to change to current modes ofpublic transit. Transport choice modelssupported by questionnaire analysissuggest that 25–30% of current carusers would be prepared to transfer toan ULTra system. It is also a systemwhich is complementary to existingforms of public transport. By providing anetwork link, it can improve theattractiveness of existing modes.

Evaluations show that ULTra can beintegrated into the urban environmentat densities which provide a usefulservice but also minimise adverseimpacts. In particular, the use ofexisting transport rights of way allows asignificant proportion of track to beplaced at grade, with little addedseverance, thereby providing cost andvisual intrusion benefits. Studies showthat ULTra can provide an immediatebenefit for use on routes beingconsidered for tram systems. It isprojected to be fully financially viable.

The system has many novel featuresfor urban transport that relate directly toimproving the quality of urban life. It iscurrently undergoing engineering testswith a view to first application in Cardiffin 2005.

In essence ULTra replaces the oldmass transit paradigm for transportwith a new paradigm based on just-in-time transit.

These ideas have frequently beenseen in science fiction. But what isdescribed here is science fact. TheULTra system of personal transportationcan be delivered using technologywhich is available off the shelf today.

Further details can be found atwww.atsltd.co.uk. ■

AcknowledgementsThe ULTra project has been supportedby the Engineering & Physical SciencesResearch Council, Rees Jeffreys RoadFund, Department of Trade & Industry,Department for Transport, NationalEndowment for Science Technology &the Arts, the Altran Foundation, CardiffCounty Council, and the EuropeanCommunity; also by the University ofBristol, Arup, AMEC and Corus. Thissupport has been fundamental ingetting the project to its present stage.ULTra is a registered trademark.

ReferencesAnderson, J.E. (1977) Transit Systems

Theory Lexington Books: Mass. Irving (1978) Fundamentals of Personal

Rapid Transit Lexington Books: Mass.Langdon (1971) ‘The Cabtrack urban

transport system’ Traffic Eng &Control Vol 12 pp 634–638

Latour, B. (1996) (Translation: C. Porter)Aramis or the Love of TechnologyHarvard UP

Lowson, M.V. (1998) ‘Surface TransportHistory in the UK – Analysis andProjections’ Proc Inst Civil EngTransp Vol 129 Feb pp 14–19

Lowson M.V. (2002) SustainablePersonal Transport Proc Inst CivilEng Municipal Engineer (5) Issue 1pp 73–82

Martin Lowson is Professor ofAdvanced Transport at the Universityof Bristol and CEO of AdvancedTransport Systems Ltd. He spent hisprevious career in the aerospaceindustry, both in the US where heworked on the Apollo Spaceprogramme and in the UK. He wasChief Scientist and Director ofCorporate Development for WestlandHelicopters. He is aco-patentee of theBERP rotor systemwhich has held theworld absolutespeed record forhelicopters since1986.