Holistic framework for optimisation of life-cycle ... · districts of Hong Kong. There are now three ATC cen-tres monitoring 1700 junction controllers and controlling traﬃc signals

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Techset Composition India (P) Ltd., Bangalore and Chennai, India THIE970747.TeX Page#: 8 Printed: 10/10/2014

HKIE Transactions, 2014http://dx.doi.org/10.1080/1023697X.2014.970747

Holistic framework for optimisation of life-cycle maintenance of the Hong Kong traffic signalsystem

Kin-Hong Chana∗, Eva Wongb, Kwok-Leung Ngc, Che-Kit Leea and Chau-fat Chana

aElectrical & Mechanical Services Department, Hong Kong SAR Government, EMSD Headquarters, 3 Kai Shing Street, Kowloon,Hong Kong; bTransport Department, Hong Kong SAR Government, 5/F, Harbour Building, 38 Pier Road, Central, Hong Kong;cTransport Department, Hong Kong SAR Government, 39/F & 40/F, Immigration Tower, 7 Gloucester Road, Wan Chai, Hong Kong

(Received 0000; accepted 0000 )

A central control traffic signal system covering 1800 signalised junctions is operating round the clock in Hong Kong forproper allocation of the right-of-ways at road junctions and safe movement of vehicles and pedestrians in the built-uparea, concentrated in less than 30% of this small city of 1100 km2. The Electrical and Mechanical Services Department(EMSD) of the HKSAR Government is responsible for maintaining this territory-wide traffic signal system, which is cen-trally controlled by computer systems installed at Area Traffic Control centres, providing optimum traffic signal timingsto minimise vehicular stops, journey times and delays of motorists and pedestrians. To optimise life-cycle management ofthese systems, EMSD implemented a holistic asset management system including compliance with the Publicly AvailableSpecification 55 as well as a geographical information system (GIS) interface with real-time asset condition represen-tations. The GIS is under development as part and parcel of the framework for further enhancement of the life-cyclemaintenance and effectiveness of the asset management system.

Keywords: traffic signal system; Area Traffic Control; adaptive control; asset management system; PAS 55; geographicinformation system

IntroductionA well-developed transport infrastructure is indispens-able for every metropolis in the world. A modern trafficsignal system serves to cut down travelling time andimprove road safety, contributing to a huge economicbenefit.A typical signalised traffic junction consists of a junc-

tion controller, lamp poles, visible and audible trafficsignals and other associated equipment such as pushbut-tons for pedestrians, signal cable and vehicle detectorloops (Figure 1).A visible traffic signal, often called traffic signal lamp,

or simply traffic lamp or traffic light, gives out threeQ2

colours of light (red, amber and green) in sequence to telldrivers and pedestrians when to stop and when they cango. Similarly, audible traffic signals provide an indicationto visually impaired persons on the prevailing pedestriansignals’ states at road crossings.The junction controller is the “brain” of a signalised

junction. It controls different phases of traffic signals.The signal time depends on traffic plans designed by thetraffic engineer. There are often several plans for exe-cution at different times of the day and different daysof the week (e.g. plans for peak/off-peak hours and

*Corresponding author. Email: [email protected]

weekdays/weekends). Real-time traffic flow is detectedby vehicle detectors embedded underneath road lanes andis used to determine optimum traffic signal timings.With the advance of intelligent transport system tech-

nology, co-ordinated control of traffic lights is now com-mon in major cities around the world. Junction con-trollers are connected to a central computer, enablingreal-time monitoring and control of traffic signals usinga pre-defined adaptive control algorithm.

Traffic signal systems in Hong KongHong Kong is a highly urbanised cosmopolitan city withthe populated area concentrated in less than 30% of thissmall city of 1100 km2. A central control traffic signalsystem covering over 1800 signalised junctions [1] isoperating round the clock for the allocation of the right-of-ways properly at road junctions for safe movement ofvehicles and pedestrians.A stand-alone traffic light was first installed in Hong

Kong in the 1960s. The first computerised Area Traf-fic Control (ATC) system started operation in 1977when ATC junction controllers were installed as a pilotscheme in Western Kowloon of Hong Kong,[2] enabling

© 2014 Taylor & Francis

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Colouronline,B/Winprint

Figure 1. Typical equipment of a signalised junction.


Figure 2. Districts in Hong Kong with ATC.

round-the-clock monitoring and controlling of the statesof traffic signals at the junctions. Road efficiency wassignificantly improved as a result and ATC junctioncontrollers were subsequently widely deployed to otherdistricts of Hong Kong. There are now three ATC cen-tres monitoring 1700 junction controllers and controllingtraffic signals throughout Hong Kong in real time accord-ing to the prevailing traffic conditions. There are other100 non-ATC junction controllers scheduled for connec-tion to these three ATC centres in the coming few years(Figure 2).

Vehicle flow information is collected by the junc-tion controller via detector loops installed beneath vehiclelanes. Vehicles are detected by means of electromagneticinduction. Real-time information such as the numberof vehicles travelling through detector loops, time gapbetween cars and the average moving speed of vehi-cles can be measured and calculated. Such informationis passed to the ATC central server for analysis. Makinguse of an adaptive control algorithm, the central serverwould automatically determine the optimised traffic planover an individual or a group of junctions based on their

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HKIE Transactions 3


Figure 3. Split, cycle time and offset time in traffic signal control.

traffic conditions, which can be expressed as a variation ofthree parameters, namely, “split” – the duration of greenlight for each approach, “cycle time” – the total time forcompleting all stages of signals for a junction and “offsettime” – the time for a vehicle driving through consecu-tive junctions, as depicted in Figure 3. The optimised planwould then be sent back to the junction controllers foradjusting the duration of green lights of different direc-tions in order to achieve area traffic optimisation. Thisreal-time optimisation, namely traffic adaptive control,can minimise traffic delay and congestion.Furthermore, with the help of CCTV cameras

installed at major road sections and junctions for trafficmonitoring, traffic signal timings can be adjusted quicklyfor individual junctions or a group of junctions by theoperators in the ATC centres to better manage trafficflows and handle ad hoc incidents. Figure 4 shows oneof the ATC centres in Hong Kong.In the case of failure of communication between the

ATC centre and the junction controller, the latter can stilloperate by its own, sending out alternate signal phasesaccording to local traffic plans stored in the junctioncontroller.It is estimated that the use of the ATC system in Hong

Kong has reduced journey time and number of stops by30%, and stopping time by 50%.[4] Fuel consumption

and pollutant emission can also be reduced by 15–18%as a result.[5]

Maintenance of traffic signal systemsThe planning, upgrading and replacement of all traf-fic signal systems are initiated and undertaken by theTransport Department (TD) of the Hong Kong SpecialAdministrative Region Government, whilst the Electri-cal and Mechanical Services Department (EMSD) looksafter their maintenance. Since its formation as the Elec-trical and Mechanical Office way back in 1948, EMSDhas been providing electrical and mechanical engineeringservices, including traffic signal systems to governmentdepartments (Figure 5).Today, a team of 60 dedicated professional and tech-

nical staff of EMSD and its contractors are responsible forthe installation and maintenance of traffic signal systemsin Hong Kong.Maintenance practice of traffic signal systems has

evolved with time. To name a few, in the past, substantialmanpower was deployed to patrol the streets for spottingtraffic signal malfunction. With intelligent networkingof traffic signal equipment with the ATC centres, trafficsignal faults can now be instantly detected in the cen-tral computer. Patrolling nowadays takes on a different

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Figure 4. An ATC Centre in Hong Kong.


Figure 5. Traffic pagoda (left), early type of traffic signal controller [2] (middle) and latest ATC-connected controller (right)maintained by EMSD.

form – it is performed en route to junctions scheduledfor preventive maintenance, and maintenance issues suchas tilted signal poles, misaligned lampheads and dirty orrusty equipment are identified, which cannot be detectedby the ATC system. In the past, there was troubleshoot-ing of controller faults and maintenance occurred downto the component level. Nowadays, junction controllersQ3

come with self-diagnostic functions that allow easy faultidentification, which hugely reduces junction down time.

Asset management of traffic signal systemsApart from equipment ageing and system expansion, traf-fic signal systems and associated equipment distributedthroughout the roads of Hong Kong are exposed to all

kinds of weather phenomena – from the dry, cool win-ters to the wet and hot summers, from tropical cyclonesto torrential rain and thunderstorms. They are also proneto direct damage by traffic accidents. Underground cablesare sometimes damaged by excavation works. With aview to improving the reliability and performance of theequipment, which is of paramount importance in ensuringroad safety, EMSD implemented in 2013 an asset man-agement system, which is based on the Publicly AvailableSpecification (PAS) 55, for the maintenance of the trafficsignal system in Hong Kong.The PAS 55 is a specification for the optimised

management of physical assets published by the BritishStandards Institution (BSI). Developed by the Instituteof Asset Management in collaboration with the BSI,

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Figure 6. Asset categorisation of a traffic signal system.

it provides clear definitions for the optimised manage-ment of physical assets. The PAS 55 was first publishedin April 2004. Since then, it has attracted widespreadadoption in utilities, transport, mining, process and man-ufacturing industries around the world, from the oil andgas industry in the North Sea to the public sector inAustralia.[6] The International Standards Organisation(ISO) also used PAS 55 as the basis for developmentof the new ISO 55000 series1 of international standardson asset management, which were published in January2014.The requirements of the PAS 55 follow the familiar

plan-do-check-act framework, similar to other manage-ment systems such as ISO 9001, ISO 14001 and OHSAS18001, all of which have already been implemented inEMSD. The establishment of the PAS 55 for traffic sig-nal systems provides a systematic and holistic frameworkfor optimisation of lifecycle management of traffic signalequipment assets. While PAS 55 emphasises on balancingperformance, risk and cost, the main objectives in imple-menting PAS 55 for traffic signal equipment in EMSDare to improve maintenance performance, sustain the reli-ability and serviceability of traffic signal equipment, andreduce the risk associated with traffic signal failure, whichhelp realise the public value of EMSD’s maintenanceservice.The assets in the traffic signal systems are categorised

in a simple two-level structure, as shown in Figure 6.All the key personnel in the maintenance team wereinvolved in interactive sessions including setting up the

asset registry, developing asset management plan, per-forming risk assessment and root cause analysis, anddrawing up risk management and contingency procedureto mitigate the risks of failure of different assets.A critical self-assessment based on past incidents

and media compliant cases was performed, followed byinternal and external audits, to ensure the robustness ofthe PAS 55 system in dealing with maintenance issuesencountered during different stages of the equipment life.The PAS 55 system for traffic signal systems was

implemented in August 2013. General improvement inmaintenance performance was observed, and the mediaattention once given to the maintenance of traffic signalsystems appears to have subsided since the implementa-tion of this asset management system.

Benefits in implementing the asset managementsystemIncreased staff alertness on traffic signal system failureThrough the participation of the key members of the traf-fic signal maintenance team in the development of thePAS 55 system and the brainstorming sessions for assetcondition assessment and risk assessment, staff awarenessof the risk and consequence, and the alertness of vari-ous failures of traffic signal systems were significantlyenhanced. All teammembers were aware of a much widerperspective of the maintenance of the system to preventtraffic signal failure.

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Better prioritisation for asset replacementThe comprehensive and regular review of asset condi-tion implemented in the PAS 55 system enabled a moresystematic prioritisation of asset replacement, and anearly notification to TD, the asset owner, for arrangingfunding for timely replacement of aged or deterioratingassets.

Enhancement in maintenance procedureFollowing detailed risk assessments, new risk mitiga-tion measures, which would help reduce failures, wereidentified and the associated maintenance procedure wasrevised and implemented. The initial statistic of fault datacollected since August 2013 showed encouraging signsof improvement.

Enhancement in monitoring and response to failureWith the critical analysis of past failures and com-plaint cases, the maintenance team identified and imple-mented a number of improvement measures, includingthe implementation of a two-tier monitoring system toensure timely feedback of repair status to complainants,enhancement of fault data collection and analysis, tak-ing immediate action to investigate in repeated junctioncontroller failures at the same junctions.

Continuous improvementAn asset management plan has been developed lay-ing down the specific tasks and activities required tooptimise performance while balancing the cost and risk.The management cycle of our Asset Management Systemis illustrated in Figure 7.The condition of each asset group, associated risk and

the failure rate over the past year will be reviewed annu-ally. Specific maintenance activities would be prioritised


Figure 7. A plan-do-check-act framework.


Figure 8. An illustration of signalised junctions on a GIS interface.

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Holistic framework for optimisation of life-cycle ... · districts of Hong Kong. There are now three ATC cen-tres monitoring 1700 junction controllers and controlling traﬃc signals