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36 Table 4-1. Situations where the guidance will apply. on tangent track. Wheel and rail roughness, caused by wear and so forth can generate a rumbling noise. Rolling noise can Ref Time Situation covered period be created if the bearing surfaces are not properly maintained. A Short term Existing system with existing vehicles Light contact of the unpowered IRWs on the track may cause B Short/ New system with vehicle designs currently available C medium Existing system, replacing vehicles with vehicle designs corrugations, which create very noisy conditions. On sharp term currently available D Medium Existing system, replacing vehicles with ones of a new curves, both flange contact and lateral slip of the wheel can /long term design occur creating wheel squeal and flanging noise. Noise may E Long term New system with new designs of vehicle also result from poor quality special trackwork. There is less space on this configuration of vehicle to install damping links. In many cases, however, information has been repeated material. from other sections of the report so that this chapter can be These issues can be managed within acceptable limits by a more easily used as a stand-alone document. combination of measures, some of which may also relieve the other issues already noted and by solutions that might only be applied locally, such as wayside lubricators on sharp curves or 4.2 Performance Issues Addressed vehicleborne friction conditioners. by the Guidance The following notes explain what the more detailed meas- 4.3 Fundamental Guidance ures described in this guidance are attempting to achieve in overall terms. Some issues apply generally or in more than one of the main areas into which the guidance has been split. These are fundamental to the situation being studied (i.e., the intro- 4.2.1 Derailment Protection duction of a technology to the United States and Canada that The main causes of derailment covered here are flange has largely been developed elsewhere). The transit systems climbing derailment and derailment on switches and cross- of other countries have adopted different standards and oper- ings. These can cause any LRV to derail, but the specific type ate in a different regulatory environment than those of the of LFLRV covered by the guidance is more vulnerable. United States and Canada. As a result, new systems in those countries do not follow the same practice. These basic facts give rise to potential risks that can be mitigated by applying 4.2.2 Wheel and Rail Wear these fundamental principles: The main causes of wear, associated with this type of vehi- cle, are Guideline 1: The vehicle supplier must fully understand the requirements of the transit system and the operating con- High guiding forces caused by poor steering capability, text and modify designs accordingly. The transit system Constant flange contact on straight track caused by lack of must facilitate this by providing all relevant information. self-centering capability, Guideline 2: The transit system must fully understand the Incompatible wheel and rail profiles, and effect of anything it specifies and not make requirements Misaligned track. that are inappropriate for LFLRV operation (e.g., the sys- tem has put forward "historical" requirements). LFLRVs using IRWs are intrinsically more prone to wear Guideline 3: The infrastructure must be suitable for the because of their dynamic performance and sensitivity to type of LFLRV to be used, taking into account features that external factors. may not appear in a written specification and may need to be modified to suit. 4.2.3 Ride Quality Successful implementation and operation will ultimately The vehicle configuration may cause the end sections to depend on all guidelines being followed in all areas. The over- pitch. Pitching can be eliminated by design of the articulation riding guidance is to emphasize the importance of achieving and linkages between the sections. There is little room on this compatible solutions to solve issues where the interface issues design of center truck for extra suspension equipment. are crucial. As mentioned above, this guidance is limited by the scope and resources available for this research program and the 4.2.4 Noise comprehensiveness of earlier studies that have been assimi- The various sources of noise can be aggravated by the use lated into it. This means that full and accurate application of of center trucks with IRWs. Rubbing flange contact will occur the guidance would not necessarily mitigate all issues likely to