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20 LFLRV Fleet been experienced, but generally track wear has not been a issue. Eighteen Siemens Avanto S70 LFLRV cars have been The system uses jointed track--noise has been experienced on supplied--delivery began in 2003. There has been over 2 years' rail joints, expansion joints, and sharp curves. There have also of experience of operating this type of LFLRV; these are the been noise issues arising from flat spots on wheels. Vehicle ride only type of vehicles used on the system. Speeds have been is adversely affected by the uneven wheel wear; it is more appar- limited to 40 mph (see below) although the cars can reach ent on tangent track. Noise and uneven ride are more noticeable higher speeds. on the center truck. Details of the Center Trucks Measures To Reduce Issues The Avanto vehicles have IRWs on the center trucks. The To overcome noise issues, MetroRail is providing continu- design uses cranked axles and a rigid center truck frame. The ous welded rail, top of rail friction modifiers, and lubrication primary suspension consists of eight conical chevron rub- of the flange ways within curves. These measures significantly ber springs mounted on the inboard side of each wheel on reduce squeal, vibration, and crabbing and, therefore, the axle flange. The secondary suspension uses high-pressure reduced noise both inside and outside the cars. MetroRail hydraulic springs that maintain the car-body floor to plat- does not see the vehicle ride issue as requiring mitigation at form height by means of six level sensors. Lateral damping present. is used, and yaw is controlled by means of resilient traction links. Three stabilizing links are used across the center sec- tion. Resilient wheels are used; Figure 2-27 shows the wheel 2.3.8 San Diego Metropolitan Transit profile. System (SDT) Eleven more Siemens Avanto S70 cars have been supplied Measures Undertaken When These Vehicles to San Diego for use on the Green Line, which opened July Were Introduced 10th 2005. This is an extension of a much larger system, which has been using high-floor cars and which opened its first Siemens undertook a computer model simulation of the route in 1981. When investigations were made for this report, route to check that the Avanto would be suitable. Speeds were only one car on the system was under test, so there was no restricted to 40 mph. experience from which to draw conclusions. Experience Using These Vehicles 2.4 Summary of Experience Wheel wear has been double the expected rate and has Table 2-7 summarizes performance issues in the United been occurring on both the tread and the flange. Some local- States to date based on the questionnaire results. The table ized track wear, associated with sharp curves in the yard, has expresses how the transit systems themselves see their issues and the extent to which they have been able to manage them "in house." Only those systems that provided questionnaire responses are included. The more serious issues (in terms of safety and cost) are occurring on the older systems, so application of this new technology to an established network can be expected to be more problematic. This seems to be mainly a function of the track geometry associated with such systems. Older systems may also need to adapt maintenance practices to suit the new types of car. Issues similar to those experienced with this type of vehi- cle in the United States have occurred in other parts of the world. Where these are known, they appear very similar. In examining the performance issues, the researchers con- sidered possible differences in practices and standards between Europe and the United States to see if there Figure 2-27. Wheel profile. was any evidence that this might have had an influence.