--.--- ._-, NOISE REDUCTION Reducingnoisefrom lightrailsystems ] .:. James Abbott, Technical Editor i 'I are Light rail systemoperators makingstrenuous anti-slip/lock mechanisms, which help in avoiding effortsto reduce d noisepollution.Careful esignof roughness of the surfaces and damaging 'flats' on vehiclesand track, and effectivemaintenance the steel tyres of the wheels (caused by skidding on policies,cancut noiseto a minimum. crushed leaves or other debris on the rail). Regular use of wheel lathes in the depot and/or grinding ./ A dvocates of light rail are keen to stress the mode's environmentally sound credentials. By drawing motorists out of private cars, light rail can reduce the antisocial effects of traffic machines on the track could be expected to help reduce roughness of wheel and rail. Hans van Leeuwen estimates that reducing roughness can give a 3 to 10 dB noise reduction. Optimising the - principally noise and air pollution as well as - wheel and rail profile can be very effective in helping the local economy by reducing reducing squeal noise. congestion and thus cutting time wasted in traffic Design and maintenance of the vehicle can be jams. As most light rail vehicles use electric important, as regards not only the wheel shape but propulsion, there is no generation of air pollution also the question of damping material between around the vehicle. But light rail vehicles can elements of the vehicle. Hans van Leeuwen found generate noise, so to emphasise those 'green' such measures can give noise reductions of credentials engineers are striving to reduce noise to as low levels as possible. A study by Hans van Leeuwen of DGMR Consulting Engineers in the Hague, The Netherlands, presented to the Euronoise conference in Naples in 2003, identified the sources of noise from light rail systems. The study found that the noise emission of a light rail vehicle is comparable to the emission of 11 cars. But to carry 100 people (assuming 66 cars are required for this number) light rail generates less noise: a light rail vehicle generates around 78 dB (A), compared to 86 dB (A) for the car alternative. between 3 and 6 dB, while for squeal noise The principal noise from light rail vehicleswas reductions could be up to 20 dB, effectively identified as coming from the interaction between the eliminating squeal noise. But he cautioned that wheel and the rail. The noise from electrical a poorly investigated or dimensioned measure machinery - compressors, ventilation systems, the might not be effective, or might even have a ,/ choppersystemand so on wasminorby - negative effect. companson. The DGMR study also found that rail and The steel-on-steel noise from the wheels and track construction is relevant for noise and rails is of three types: rolling noise, impulse noise vibration emission. Reductions of up to 4-6 dB can and curve squeal noise. The noise is released both be achieved by shape optimisation, the addition of into the air and, through vibration, into the ground a damping material and optimisation of rail pads. and adjacent buildings. Again, these measures can help in the reduction of Hans van Leeuwen advocated reducing the squeal noise. roughness between the wheel and rail as the most effective mechanism for reducing noise. Most Track design mnnprn lipht r>1il vphirlp~ h>1VP r1i~r hrCllcp~ Cln.1 rla""l" tho l;..ht ",,;1 an..;nao,. q;~;n.. t~ 1TOO~ n~;nq emissions to a minimum will pay close attention to emerged. They found that there are a number of the design of the track. The Parsons Brinckerhoff acceptable styles, but there are also design issues consultancy was awarded a contract by the that need resolution. Transportation Cooperative Research Program in Electrical isolation of the rail as a means to the US to research best practice from light rail mitigate the effects of stray current corrosion is still a systems around the world, with a view to major factor in design of the track system. The rails producing a guide to designers of new systems. A act as the negative return current conductor, with study team led by Parsons Brinckerhoff's Gordon electrical current running through the rails to the Martyn researched light rail systems in Belgium, substation to complete the circuit. Stray current France, Germany and the US. Three types of track problems can arise with little or no insulation of the were identified, as follows: rails because some traction current could leak into the structure and ground to travel back to the Embedded track, as found on street-running sections substation. Buried metallic water and gas pipes or The team found that designs of embedded track cables provide a lower resistance path for stray have improved as new light rail systems have currents. When the currents leavethe buried metal lines, corrosion of the utility pipes occurs. This ALH Rail Coatings Limited 'Series Six' pre corrosion can be catastrophic. Newer insulating coated rail system is the choice of clients, materials and an understanding of stray current designers and contractors for UK tram systems. control requirements are helping to resolve this issue. Midland Metro (Centro), Manchester Metro Another area of concern is failure of the paved Phase II, Nottingham Transit Line 1 (NET) and surface: clearly, even if a light rail vehicle is emitting Dublin's LUAS all chose this system.. little noise, if a poor road surface caused by the Factory pre coating ensures very high levels light rail track is increasing road vehicle-generated of rail cleanliness by grit blasting and immediate noise, the whole system can be reckoned to have priming; in an ideal environment. Combined failed. Embedded track observed by the Parsons these measures ensure that 'Series Six' Brinckerhoff team was in a variety of pavement polyurethane polymer is fully bonded to rails sections, ranging from bituminous asphalt and thus providing the highest levels of electrical flexible cobblestones to very rigid concrete, all of insulation, preventing stray currents. which are relatively successful. The pavement type Granite chippings or bauxite, both chemically that works in a warm, dry climate, however, may treated with an adhesion promoter can be not work well in a cold, wet area with freezing and incorporated in 'Series Six' polymer, providing roadway salting, both of which affect pavement and increased skid resistance at the road surface, track life span. In these colder and wetter climates, another important safety benefit of the ALH special consideration must be given to surface Rail Coatings Limited system. pavement design, especially surface and internal drainage, to mitigate freeze/thaw-cycle damage. Another issue is excessiverail wear and corrugation (the formation of undulations on top of the rail head that result in rough and noisy operation). As Hans van Leeuwenfound, the interface between the wheel and the rail is a critical area. Directfixation(or slab)track, where the track is embeddedin concrete This system can incorporate drainage boxes and rail bonds within the 'Series Six' polymer This design has become more prominent in the and is completed with stray current collection past two decades as an economical application for mat, reinforcing steel, concrete and a finishing tunnels and aerial structures. The light rail system layer of asphalt, paving blocks or concrete which managers visited by the Parsons Brinckerhoff study may be coloured to enhance appearance. team found that direct fixation helps to reduce Working with Hyperlast's technologists plus maintenance and increases electrical isolation. rail and tram partners ALH Rail Coatings Limited Conventional ballasted track continues to develop products and systemswhich include materials for in situ pouring, installation This is the predominant track type for locations on sleepers,sleeperboots and grass track for an within an exclusive right-of-way. In general, it environmentally friendly solution. performs well. There are many different types of sleepers and fastenings in use. The need for - I eurUtfd""f..IUrr' 60 'I iii --- NOISE REDUCTION electrical isolation to prevent stray current that are visually intrusive and very expensive.The corrosion has had an impact on the designs system has undergone extensive trials on a full-scale of fastening systems. test track in the Czech Republic and has been installed at two sites in The Netherlands and one in Corrugation France. Trials have shown that a reduction of about Corrugation, says Gordon Martyn, remains a six decibels can be expected. serious concern in maintaining rail on any type of Corus' Silent Track tuned rail dampers can be system. Light rail systems appear to suffer from either installed 'on track' onto rail that is already in short wave (roaring rail) corrugation, which causes service, or in factory conditions onto rail that is to substantial noise. Corrugation appears most be used in renewal or new-build programmes. Corus frequently at steep grades, sharp curves and and Volker Stevin Rail & Traffic have developed a stations. While changes in rail and wheel metallurgy technique for installation that minimises possession may impede the propagation of corrugation, it times and ensures the integrity of the installed appears that a regular programme of grinding can product. Factory fitting of Corus tuned rail keep this problem under control. The track designer dampers can be achieved at a location convenient to needs to factor this maintenance operation into the the client, for example onto long-welded rail strings design of embedded track, where grinding wheels at a welding facility, or at one of Corus' own sites. may strike high pavement. Track design items Noise generation has been an issue for some urban rail systems in North America, for instance in San Francisco and Washington, and also in Europe. 'The use of direct fixation fasteners, ballast mats, and floating slabs are some of the solutions that are being used to make light rail an unobtrusive neighbour' says Gordon Martyn. A number of companies have developed products to respond to this demand. ALH Rail Coatings Ltd, a joint venture between Hyperlast Ltd and GrantRail Ltd in the UK, supplies polymer pre-coated rail systems.The company's patented 'Series-Six'rail encapsulation is a two- Corus' Silent Track system has the ability to be component modified polyurethane system providing 'tuned' to absorb vibrations specific to a particular acoustic dampening of frequenciesthat generate rail track form. It has a multi frequency response over noise; this technology is particularly beneficialin the important acoustic range for rail noise and offers urban areas. Hyperlast's polyurethane elastomer noise reductions of 5-7 dB, depending on track form technology has been used to develop a product with and condition. There are no maintenance high flexibility,long-term resistance to abrasion, tear, requirements and no effects on other elements of the water, acids and alkalis, as well as electricalinsulation rail infrastructure, the product has the same life as and vibration absorption properties. the rail itself, and there is no interference with other Anglo-Dutch steel company Corus has track maintenance activities,such as tamping. The developed the Silent Track noise reduction rail system is visually unobtrusive and eliminates or system, which significantly reduces noise generated reduces the need for acoustic barriers. by railway traffic. The system reduces noise I generated by rails as train wheels pass over them by Acoustic barriers ]' employing 'tuned dampers', developed in While the bulk of this article has concerned the I conjunction with Southampton University's reduction or elimination at source of noise from " Institute of Sound and Vibration Research, which light rail systems, the other possibility is to contain are attached to either side of the rail. These dampers the noise close to the track by erecting acoustic efficiently absorb vibrations and hence prevent noise barriers in between the track and adjacent from being generated by the rail. The tuned damper buildings. Hans van Leeuwen of DGMR estimates can be fitted to a variety of standard rail sections, that separationsin the propagationpaths - through which makes it a significantly more attractive option open air or vibrations in the ground - can effect than noise containment measures such ~s h~rri"'rs r",clllrt;on"of lln to 1"irlR .
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