Towards a Quieter Construction Environment 02

Reconstruction of Vehicular Bridge at ECP across Siglap Canal 04

Safe Working at Height 06

Safe Braking Distance in Rapid Transit System (RTS) with Decreased Headway 08

Use of Reflective Markers to EnhanceRoad Safety 10

Accident Statistics 11

SAFE WORKINGAT HEIGHT

Issue 7 | ISSN 1793-1665 | March 2007

SAFETYNEWS

Towards a Quieter Construction Environment

Construction Noise in Singapore Today

Singapore strives to be a world class global city. With several mega projects such as the Circle Line, Downtown Extension Line, the Integrated Resorts and Marina Barrage projects being put in place, Singapore promises high quality living for her residents.

However, before the realisation of all these projects, if not properly managed, the inevitable noise emissions from construction sites will compromise the desire of an ever affluent community that appreciate quieter and more peaceful rest hours. Indeed, recently this challenge prompted NEA to review and propose more stringent allowable noise limits.

Noise Management at LTA Construction Sites

Construction activities are inherently noisy and it is a challenge to maintain working noise levels to the existing night time allowable limit of 60dB which will be further reduced to 55dB, considering that 45-50dB is what a quiet office environment will be. Practically, no works of construction can be carried out during the night. Taking on this challenge in control of noise emission, LTA adopted a systematic and pragmatic approach.

The first principle in controlling noise is the elimination or reduction at source. This includes the use of quieter equipment such as silent pilers, sound-reduced generators and newer machinery.

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Figure 1: Inside of machinery cover lined with acoustic material

Figure 2: A sound-reduced generator set

After reducing noise at source, we next examine effective means of attenuating noise transmission before it reaches the nearby residents. Noise barriers are extensively used in LTA sites; they are either lined along the top of our site hoardings or placed at face of specific noisy activities as well as noise emission outlets.

LTA has further stepped up noise control effort in new infrastructure projects such as the Downtown Line. Stringent requirements have been put in place that require the use of noise modelling tools for pre-construction environmental impact assessment. Noise management software allows us to identify noise sensitive receivers and pinpoint locations where noise barriers can be appropriately used.

Noise Monitoring at LTA Construction Sites

Many assumptions can be derived in the planning stage regarding possible noise emission magnitudes and the associated noise mitigation measures for major construction activities but this is never exhaustive as construction site environment varies, so are construction works over time. Therefore, it is mandatory that continuous monitoring is carried out to ensure that measures taken are working effectively. To ensure that we comply with the

Figure 3: Noise panels installed at noise emission outlets to reduce engine noise

Figure 4: Noise barriers installed along top of site hoardings to reduce overall noise emission

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>>stipulated allowable limits, permanent noise monitoring devices are placed at selected noise sensitive receivers. These points of monitoring are to be acknowledged by NEA to ensure that the noise dosimeters capture reasonable readings from our sites.

In addition to noise monitoring at permanent locations, monitoring is also carried out using portable devices at selected sites in the evenings. This allows us to react immediately should noise emission from our works exceed the allowable limits. Contractors will need to implement temporary noise mitigation measures such as the use of portable noise barriers or reschedule their work to other times of the day if feasible.

Engaging the Community

LTA takes pride as an engaging public developer to reach out to the community around our work sites. We distribute informative newsletter to residents, update them on the good practices we have implemented and inform the community in advance if work needs to be extended into the late evening by sending out circulars timely.

Figure 5: Our contractor carrying out ad-hoc noise monitoring for diaphragm wall construction in the evening

Figure 6: Community bonding session show-casing the efforts in ensuring all environment nuisances are minimised.

Conclusion

With the society getting ever more affluent and working life getting more stressful, generally there is a greater desire for quieter and peaceful rest hours, especially in late evenings and weekends. Through our active engagement, LTA understands that our community do appreciate the efforts we have put in to enhance our land transport network with their convenience in mind. For instance, they have tolerantly put up with the disturbance related to certain work activities such as diaphragm wall construction that may have to be completed, at times, beyond the usual work hours for safety reasons.

Nonetheless, we at LTA are equally mindful that during certain critical periods such as examination weeks and public holidays, major noisy construction works should be avoided. So far such an understanding and cooperative approach benefits LTA, our contractors and the community in advancing our major projects.

Construction noise management is both a science as well as an art. Sound engineering knowledge of noise propagation and skilful techniques of noise mitigation is a must, but without sincere and effective public relations to engage the community, construction works will take longer and project completion dates will be delayed and extended.

LTA is committed to put in more efforts and resources to manage noise emission from our sites. Through effective consideration and incorporation of noise management issues into our construction programmes, and the ever pervasive engagement of our community, we are confident that our community will be able to enjoy the benefits of our land transport infrastructure at their earliest possible completion dates.

By Matt, Chew Boon BwanEngineer, EnvironmentalSafety Division

Reconstruction of Vehicular Bridge at ECP across Siglap Canal

Introduction

The existing vehicular bridge across Siglap Canal at the East Coast Parkway (ECP) near Exit 8B to Marine Vista is undergoing major transformation through demolition and reconstruction (Fig.1 location plan). Contract RD123 is part of the islandwide bridge upgrading programme to cater for enhanced vehicular loading.

The Contract includes demolition of the existing bridge and construction of a new single span bridge in the same location, without closing the carriageway or disrupting normal traffic flow along the expressway.

With the tight working corridor bounded by the existing pedestrian overhead bridge supports on both sides of carriageway near the vehicular bridge, restriction on felling of mature trees at the road sidetable/center median and closeness of worksite to the major traffic exit at Marine Vista, the project team faced tremendous challenges in planning and implementing a safe work zone right in the middle of a high speed expressway. Apart from these physical constraints, there are also environmental considerations that need to be addressed due to close proximity of the worksite to the nearby residential blocks and school.

Planning for Safe Work Zone

Figure 1: Location plan

with each involving detailed survey to identify work space, construction access, minimal safe sight distance for motorists, determination of limit of work zone for demolition and reconstruction activities, etc.

An independent traffic safety consultant was engaged to review the contractor’s temporary traffic diversion design. The final design was then put-forth to LTA’s Project Safety Review (PSR) Committee for endorsement and subsequent implementation at site.

The 3 stages of work (stage 1, 1a & 2) are illustrated as follows:Stage 1

This involved the lateral shifting of 3 traffic lanes at both bounds towards the center median. Under this stage, part of the existing bridge was demolished and foundation piling and deck superstructure for the outermost edge of the new bridge were constructed. Upon completion of this stage of work, the new bridge deck was used to accommodate one traffic lane for diversion.Stage 1a

The ideal work zone for such demolition and reconstruction work would be to divert the whole carriageway laterally in one go so that all construction activities could be confined within the hoarded boundary. This is obviously not feasible here and therefore the project team and contractor had to study various alternatives and look for an optimal solution that could satisfy all constraints encountered at site. The optimal way adopted is to plan the work zones and construction activities into stages.

Three stages of work are therefore planned,

(Stage 1 Traffic diversion and work zone)

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(Stage 1a Traffic diversion and work zone)

This intermediate stage was the most critical due to the need to split the traffic lanes i.e. slow lane onto the new bridge deck completed under Stage 1. It was necessary to create a narrow work zone within the split lanes to demolish part of the existing bridge and install foundation pile and bridge deck of the new bridge. The completed new bridge deck in combination with that completed under Stage 1 were used to accommodate all 3 traffic lanes for the next stage of work.Stage 2

This stage involved the lateral shifting of 3 traffic lanes at both bounds towards the outer edge so that the remaining part of the existing bridge at the center median could be demolished and reconstructed.

Monitoring and Control of Work Zone Safety

At each stage of work, detailed safety plans including signs, traffic control devices, worksite access control and workmen safety are implemented. These are cascaded to all levels of site management and workmen, their duties and responsibilities defined and daily checks carried out by both the contractor and the project team.

(Stage 2 Traffic diversion and work zone)

Apart from worksite safety, the traffic condition along ECP is also being monitored closely, both from the site as well as remote monitoring through Intelligent Transport Systems Center (ITSC) to facilitate detection and control of any disruption to

traffic flow during the work.

Enhancing Safety by using Variable Message Signs (VMS)

To guide motorists with advance information on traffic realignment and conditions, Variable Message Signs (VMS) are installed at both approaches of the work zone. These versatile alphanumeric displays are programmable and capable of providing realtime control message to meet the needs of the worksite. Two battery powered VMS of 2.5m x 1.8m dimensions are strategically located at the road sidetable and gore area of lane split at each approach of work zone. The use of VMS are very effective in providing advance information prior to traffic realignment, during temporary lane closure, construction access control and during inclement weather / night conditions.

Conclusion

Works on the demolition and reconstruction of existing bridge across Siglap Canal at ECP has currently progressed into Stage 2. Work for Stage 1 and 1a had been completed without disruption to traffic or resulting in any construction accident. Safety will remain top priority of the project team and contractor till the final completion of work in the 2nd quarter of 2007.

By Lau Hwa CheongProject ManagerRoad Development

Control of work zone safety for Stage 1a diversion and use of VMS at gore area of lane split

VMS on portable stands at side table

By Cheang Wai KiongHigher Principal Engineering Officer Road Development

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Safe Working at Height

Introduction

Working at height is by its very nature hazardous and the risk is often exacerbated by the lack of proper risk assessments and safe work procedures.

A fall from height accident could result in serious injuries or fatality. Even when not fatal, such injuries very often have a serious impact on the victim’s future working and family life.

Accident statistics showed that ‘falls from height’ is the most prominent type of fatal industrial accident in Singapore, accounting for 34% of fatal industrial accident from 2002 to 2005, with the construction sector accounting for 51% of these fatal falls.

What is Working at Height?

Many associate the requirement for preventing falls to only apply when working above ground level. However, this is not the only area where a fall can result in injury. Falls into excavated trenches or uncovered bored holes are some other forms of such hazard. Therefore, a work place is deemed as being ‘at height’ if a person could be injured falling from it, even if it is at or below ground level.

Workplace Safety And Health (General Provision) Regulations 2006 requires reasonably practicable measures, such as provision of secured foothold and handhold, to be put in place where a workman is liable to fall a distance of more than 2 metres.

Risk Management and Fall Prevention Control

Prior to commencement of any work at height, a risk assessment must be conducted in relation to the safety and health risks posed to any person who may be affected while carrying out the work.

The assessment process will involve the identification, evaluation, mitigation and control of the potential risks. Risk control strategies are then applied to reduce the risk to an acceptable level. The hierarchy of these strategies are in the following order, with higher level (level 1) methods preferred over the lower ones:

>>Level 1 : Elimination – remove it completely. For example, prefabrication of roofs at ground level.

Level 2 : Substitution – replace with a safer alternative. For example, the use of precast concrete over in situ casting.

Level 3 : Engineering controls – use suitable tools or equipment to reduce the risk. For example, use of aerial work platforms and physical barriers.

Level 4 : Administrative controls – established a system to control work process. For example, the Permit To Work (PTW) and Safe Work Procedure (SWP) system.

Level 5 : Personal Protective Equipment (PPE) – the last option after all the other levels of control are considered. For example, the use of travel restraint system (safety belt) and fall arrest system (full body harness). PPE should be considered as an added protective measure.

The travel restraint system limits the travel distance by securing the fixed length lanyard to an anchorage point.

The fall arrest system is designed to catch and hold a person in the event of a fall.

Reference: Technical Advisory For Falling From Height, Ministry of Manpower

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Common Observations

Provision of proper work-platforms with toe boards and guardrails.

Provision of designated work access.

Provision of continuous barricades with toe- boards and netting.

Provision of well maintained walkway and access.

No proper work-platforms and workmen were placed in a compromised position.

No proper means of access and no provision of proper work-platforms.

Bored hole shall be barricaded or covered to prevent unknowing workman from falling into it.

Ladder used shall be of good construction and made of sound material. Self-fabricated ladder is prohibited at LTA’s worksites.

Foot-hold not fully boarded nor effectively guarded to prevent workmen from falling through.

Conclusion

Fall from height can be prevented and this can be achieved by conducting a comprehensive risk assessment to identify all possible hazards and to take all reasonably practicable steps to manage if not eliminate the foreseeable risk.

By Lee Ngee Hock, DavidExecutive, Safety Division

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Safe Braking Distance in Rapid Transit System (RTS) with Decreased Headway

Introduction

For a train to travel safely on a railway, its braking system must interface with the signalling system to control and ensure that trains have sufficient distance ahead for it to decelerate and stop safely.

In order to meet the increasing passenger demand during peak hours, shorter headway is always desired. For a rapid transit system operating with decreased headway, safe braking is therefore of paramount importance. This article examines the principle of safe braking from the train and signalling systems’ perspectives to provide readers with a better understanding of the measures that have been incorporated in our rapid transit systems.

Before going into the principle of safe braking distance, a short description on the train braking system is provided below.

Brake System

The brake system on our train comprises of regenerative braking system and pneumatic friction braking system. Both of which are commonly known as electric and pneumatic braking system respectively.

Electric braking utilizes the traction motors of train to retard motion. During deceleration, the traction motors act as generators, converting the kinetic energy of the train into electricity. The electricity generated is then fed back to the power supply network for use by other trains.

Pneumatic braking is an air-operated friction brake system which utilises tread brakes to retard the rotation of the wheels on the bogies. There are four tread brakes on each bogie (i.e. one set per wheel).

The normal braking sequence in the train is to first apply electric brakes to reduce the speed of the train. Then pneumatic brakes are gradually blended in when train speed falls below 12 kph and at 8 kph and below, only pneumatic brakes are applied to stop the train.

The design of the brake system is based on a fail-safe approach. For instance, in the event of

Traction Motor mounted on a bogie

malfunction of critical systems of the train, an emergency brake would automatically be applied to bring the train to a standstill.

The design of the brake system also takes into consideration the following:

• Modular Concept to ensure ease of maintenance whilst also ensuring that no single failure of the brake system could result in a loss of braking effort on more than one bogie.

• Wheel Slide Protection to minimise wheel locking and sliding during braking on wet tracks.

• Load Weighing System to ensure that braking effort applied is proportional to the car and passengers load.

How to Achieve Safe Braking in Rapid Transit System

In order to achieve safe braking in rapid transit systems, it is essential that the signalling system and braking system work closely together.

The design of the signalling system for the safe braking calculation is very much dependant on brake assurance given by the train system such as the full-service brake rate.

The full-service brake is the maximum deceleration rate so as to minimise the risk of injury to passengers or cause damage to the train.

How Safe Braking Distance is Determined

Braking distance is defined as the distance the train travels from the point when the train driver (or Automatic Train Protection (ATP) system) makes a full-service brake application to the point where the train stops.

The braking distance is dependant on:

• the speed of the train when the brakes are applied;

• the deceleration rate available with a full-service brake application, which varies according to the coefficient of friction between the wheel and the rail;

• the Automatic Train Control (ATC) reaction time and mechanical brake reaction time;

4 tread brakes per bogie

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• the geometry of the track, in particular, the track gradient the train is travelling over from the location when the brakes are activated to the location where the front of the train stops;

• the mass distribution of the train; and• the overhang distance between the train

antenna and the front of the train.

How Safe Braking is Applied to the RTS

Fixed-block signalling system is used on the existing North-South/East-West line. In a fixed-block system, the rails are electrically divided into blocks. Track circuits are used for the detection of train occupancy. Trains are detected by the wheels and axles of a train shorting a low-voltage current inserted into the rails. The signalling system figures the position of a train by the simple measure of block occupancy. Track circuits also form part of the ATP system by transmitting speed code to the train via the track. Train detection method using track circuit is based on fail-safe principle. In the event of track circuit failure, that particular block would be classified as occupied and zero speed code would be injected to the track in rear, hence preventing trains from entering the affected block.

How to Decrease Headway in the RTS

Headway is defined as the elapsed time between trains travelling at maximum permitted speed passing a fixed point in the same direction over the same track.

Headway can be shortened if the length of the fixed blocks can be reduced or be tagged to a fixed distance from the tail of the preceding train, so that the distances between trains vary according to their actual speed and in relation to the train ahead.

To achieve this, a moving-block signalling system is used rather than a fixed-block system. Through a continuous two-way communication between trains, a precise knowledge of the trains’ locations, speeds and geometries of the track is obtained. Based on this information, a computer onboard the train can calculate the next stopping point of each train and command the train to brake, accelerate, or coast accordingly.

For North-East Line, the moving-block signalling system uses a radiating waveguide system installed along the side of the track. This waveguide

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~Transmitter Receiver

Axle of

train

carriage

Train wheels short-circuit

passage of current to receiver

To Signalling circuits -

De-activate relay when

train short-circuiting

rails

General Principles of Track

Circuit

78/77

78/77 78/61

62/39 40/0 0/0

(Overlap)

Headway

Fixed Block signalling system for existing SMRT

Braking Distance for 78 kph

Speed Code definition

MSS/TS = Max. Safe Speed within the block / Target Speed exiting the block

e.g 78/77 means that the train is allowed to travel at a maximum speed of 78

kph within the block and it must reduce to 77 kph or below before entering to

the next block.

Braking Curve

Braking Curve

Trackside equipment

Moving Block signalling system for NEL

~Transmitter Receiver

Axle of

train

carriage

Train wheels short-circuit

passage of current to receiver

To Signalling circuits -

De-activate relay when

train short-circuiting

rails

General Principles of Track

Circuit

78/77

78/77 78/61

62/39 40/0 0/0

(Overlap)

Headway

Fixed Block signalling system for existing SMRT

Braking Distance for 78 kph

Speed Code definition

MSS/TS = Max. Safe Speed within the block / Target Speed exiting the block

e.g 78/77 means that the train is allowed to travel at a maximum speed of 78

kph within the block and it must reduce to 77 kph or below before entering to

the next block.

Braking Curve

Braking Curve

Trackside equipment

Moving Block signalling system for NEL

provides a continuous transmission medium for communication between the train and trackside computers for the information on the train location, speed and direction of travel. In the event of a breakdown in communication link, the emergency brake will be applied automatically to bring the train to a standstill.

Conclusion

A long braking distance would increase the headway of the line and is therefore, less desirable in meeting increasing demand during peak hours. With newer technology such as the moving-block system, it is now possible to have a shorter headway and still maintain the safe braking distance.

The rigour with which fail-safe principles are applied on the signalling and train braking systems in our rapid transit systems plus the use of automation to remove the possibility of human error, makes our rapid transit systems extremely safe.

By Paul Cheong Chin YewExecutive EngineerRolling Stock Division

By Ang Seng HongSenior Engineer, SignalsSignals, Communications and Control Division

waveguide

~Transmitter Receiver

Axle of

train

carriage

Train wheels short-circuit

passage of current to receiver

To Signalling circuits -

De-activate relay when

train short-circuiting

rails

General Principles of Track

Circuit

78/77

78/77 78/61

62/39 40/0 0/0

(Overlap)

Headway

Fixed Block signalling system for existing SMRT

Braking Distance for 78 kph

Speed Code definition

MSS/TS = Max. Safe Speed within the block / Target Speed exiting the block

e.g 78/77 means that the train is allowed to travel at a maximum speed of 78

kph within the block and it must reduce to 77 kph or below before entering to

the next block.

Braking Curve

Braking Curve

Trackside equipment

Moving Block signalling system for NEL

General Principles of Track Circuit

Introduction

Reflective markers are fitted on long vehicles in many countries to enhance their conspicuity on the roads and hence improve road safety. In Singapore, the uses of such markers on long vehicles were made compulsory since 1981 and these vehicles are required to be fitted with reflective rear and side markers.

With technological improvements in the materials used for these markers and its increasing use world-wide to make long vehicles more conspicuous to other road users, LTA had, in 2005, revised the requirements for the rear and side markers for long vehicles.

In addition, LTA has also introduced the use of reflective signs for school buses in 2005 to make them more prominent and alert motorists on the presence of children boarding or alighting the school buses.

Enhanced Rear and Side Markers Requirements for Long Vehicles

Since 1 August 2005, all newly registered long vehicles are required to have rear and side markers that meet the enhanced marking requirements. The enhanced marking requirements are:

• Durable rear and side markers with high retro-reflective properties, complying with the technical specifications set out in UNECE Regulation Number 104;

• The colour for rear markers shall be in red and the side ones in yellow, instead of the chevron colour scheme of alternating red and yellow stripes for both markers; and

• Long vehicles shall have three yellow side markers (instead of just one) fitted on each side of the long vehicle / trailer.

Owners of long vehicles registered before 1 August 2005 will have up to 31 July 2007 to replace their vehicles’ markers to comply with the enhanced requirements.

With these changes, the following requirements are being lifted:

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Use of Reflective Markers to Enhance Road Safety

1 red rear and 3 yellow side markers

• The "Long Vehicle" sign previously required for goods vehicles and trailers with overall length exceeding 13 meters; and

• The use of flank lights for trailers.

Affected long vehicles include goods vehicles that are more than 10 meters and trailers that are more than 5 meters. New mobile cranes that exceed 10 meters in length are required to fit the red coloured rear markers.

Reflective Signs on School Buses

Since 1 July 2005, LTA has required all buses licensed to carry school children to have the following additional safety devices installed:

a) Automatic activation of the bus hazard warning lights when the entrance or exit door is opened; and

b) Reflective triangular ‘Children Crossing’ sign with red LED (Light Emitting Diode) blinking lights at the rear of the bus. The LED lights will flash when the entrance or exit door is opened.

These added safety devices serve to caution other motorists that children are boarding or alighting from their school buses.

Conclusion

Reflective markers are used on long vehicles and school buses to enhance road safety in Singapore. LTA takes a serious view of safety and will continue to regularly review the reflective marker requirements on vehicles to improve road safety.

By Roy LeeDeputy ManagerVehicle Engineering Division

Reflective Children Crossing Sign with red blinking LEDs

Automatic activation of hazard warning lights

The reflective “Children Crossing” sign is made of retro-reflective material that complies with ASTM Standards D4956 Type VII, Type VIII or Type IX, to make the school buses more conspicuous to other motorists on the roads.

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*Based on Workplace Safety and Health Act (WSHA) requirements^ 2006 Industry Figures are not available at time of print.

By Tham Chee HooHigher Engineering OfficerSafety Division

>>Accident Statistics* from January 2006 to December 2006

Editorial Page>>Construction Staff Safety Award (CSSA) on 17 November 2006

The annual CSSA gives due recognition to LTA officers who have demonstrated pro-active attitudes and exemplary safety conscious efforts towards safety and health issues at their workplace.

The CSSA winners with CE, from L-to-R:Teo Jieh Ping (C821/822) , Teo Beng Sai (C823/828), Mahesh Pandarinath Shelke (CCL4&5), CE BG(NS) Yam Ah Mee, Chew Kheng Huat (BLE), Tan Beng Tiong (Roads), Kelvin Kwek (KPE), Jasper Phua (CCL E&M). Not in Picture: Carlos Pagdanganan Roque (C825), Ben Tan Tuang Ho (CCL3).

Assessment of LTA’s Occupational Safety and Health Management System (OSHMS)

LTA engaged DuPont Safety Resources to conduct an independent assessment of its OSHMS in January 2007. The auditor assessed LTA’s OSHMS and benchmarked its safety performances against the best practices of other organizations in the construction industry worldwide, typically for land transport infrastructure developers.

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EDITORIAL COMMITTEEAdvisor Corporate Safety Committee

EditorLee Ngee Hock, David

Writers Roy Kee | Lau Hwa Cheong Cheang Wai Kiong |Ang Seng Hong Cheong Chin Yew, Paul | Tham Chee HooChew Boon Bwan, Matt | Lee Ngee Hock, David

Circulation OfficerTan Chee Lang

Congratulations to the following LTA Contractors:

• Woh Hup-Shanghai Tunnel Engineering-Alpine Mayreder JV (Contract 855) for achieving Silver Award at MOM’s Annual Safety and Health Performance Awards 2006.

• Sembawang Engineers and Constructors Pte Ltd (Contract 856) for achieving Silver Award at MOM’s Annual Safety and Health Performance Awards 2006.

• Samsung Corporation (Contract 423) for achieving Bronze Award at SCAL Innovation for OSH Awards 2006.

Excavator used in excavation pit must be

equipped with reinforced cabin roof that is capable of withstanding impact from

falling objects.

Safety Ong says...

Contributions or feedback to:Land Transport Authority, Safety DivisionNo.1 Hampshire Road, Singapore 219428Tel: (65) 6396 1127 Fax:(65) 6396 1071

Email : ngee_hock_lee@lta.gov.sg

DuPont’s auditor, Mr. James O. Faulk, during his site visit to ER141.

Group photo with DuPont Safety Resources after the delivery of their closing meeting with

LTA management.

Safety News is also available online at http://internet-stg.lta.gov.sg/Projects/index_proj_safety.htm