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25 Portland MAX has experienced higher LFLRV wheel flange significantly, this will worsen rolling noise, but conformity can wear on the center truck than on the motor trucks (Section cause corrugations, generating noise issues as noted above. 2.3.1). MBTA's Green Line experienced rapid wheel wear on There is a relationship between the wheel-rail contact area all trucks of the Type 8 cars, and experienced excessive rail and noise because of "contact stiffness,"but noise does not vary wear on its very sharp curves from all cars (Section 2.3.2). The significantly over a large range of contact stiffness variation. Newark Subway has had higher wheel wear on the center Frequent truing of wheels will avoid issues in this area (10). trucks of its LFLRV fleet than on the wheels of the motor In general, rails and wheels radiate noise. The ties tend to trucks and has very high rail wear on sharp curves (Section dominate at low frequencies, rail at mid-frequencies, and 2.3.3). NJ TRANSIT's Hudson-Bergen line, Santa Clara VTA, wheels at high frequencies. Resilient wheels will radiate less Houston Metro, and San Diego did not report issues in the noise. The reflectivity of a surface is also important, so questionnaire responses but, in some cases, it was too early to although ballasted track tends to radiate more noise because have observed this issue. of the exposure of the rail web, the ballast tends to absorb this better than a smooth road surface. Corrugations may be more likely on light rail because of 3.3.3 Solutions light contact patch loads and lack of variation in wheel diame- On the type of LFLRV being studied, the use of IRWs on a ter (but experience is that variation in wheel diameter worsens short articulated section introduces the risk of increased wear issues generally). Where corrugations occur, the ability of angle of attack. The wheel-rail interface is critical for all LRVs, the wheel to follow the rail profile is critical in terms of noise, but for these types of vehicle it is also necessary to control the so suspension/truck stiffness becomes a contributory factor. relative position of wheel and rail more closely so as to over- All noise is significantly increased by resonance effects, so come this "flexibility." whatever can be done to reduce these will be important. Measures that reduce wheel and rail vehicle wear (e.g., Noise occurs on curved track because of the lateral slip of lubrication) are more likely to be required if this type of vehi- the wheel tread across the railhead and by contact between cle is used, and this may increase costs. For new systems, it is the wheel flange and the gauge face of the rail. Squeal or howl possible to avoid the extremes of track geometry that have will be the only noticeable wheel-rail noise on sharply curved caused these issues on older systems. track because cars will be moving slowly. Such noise is likely to be an issue on older systems with curves, which are sharper than modern LRVs are usually designed for, and LFLRVs are 3.4 Noise the first modern cars to be introduced. Flange contact is important with IRWs because their lack 3.4.1 Basic Causes of self-steering ability leads to the generation of high angles IRWs generate more noise on tangent track because their of attack, which in turn leads to higher noise levels being lack of any intrinsic steering ability allows rubbing flange generated. contact to occur. The noise generated by this is likely to be Squeal is sustained non-linear wheel oscillation and will particularly noticeable in the vehicle because of the proxim- only occur if the damping capabilities of the wheel are poor. ity of the floor to the noise source and the difficulty of pro- This is unlikely with modern designs of LFLRVs which, in ducing a successfully noise-inhibiting design within the common with other modern LRVs, are likely to use resilient constraints of an LFLRV. The more complex body shape, with wheels. two floor heights, makes noise suppression more difficult, but Noise emanating from special trackwork can be significant, this effect is hard to quantify. even though obviously localized. LFLRVs may be worse in Noise can result from wheel-rail roughness and, therefore, this respect if they use significantly stiffer suspension than can be a secondary effect of wheel-rail wear (see above); conventional vehicles. wheel-rail roughness includes track corrugations and the extreme condition of wheel flats. Rail roughness tends to 3.4.2 Experience with Noise dominate over wheel roughness. IRWs are more sensitive than conventional wheelsets to wheel flat development Traditional streetcar lines were characterized by noise; because adhesion during braking cannot be shared across an unfortunately, many new light rail systems have experienced axle and because of the low rotational inertia of the wheels. noise issues, despite technical advances and effort at the For all rail vehicles, rolling noise (the inevitable but not sig- design stage. The U.S. transit systems using LFLRVs, however, nificant base level noise) can be worsened by periodic grind- have not generally experienced any significant issues that can ing if such grinding does not achieve an adequately smooth be directly related to the use of this type of car. rail surface. Rolling noise will also be affected by the support MBTA and Houston Metro have experienced a noisy envi- stiffness of the rails. If the rail head and wheel profile vary ronment in the vehicles but have either found solutions or