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CHAPTER 3
Performance Issues and Causes
3.1 Overview forces holding the wheel down on the rail are exceeded by
the lateral forces, causing the flange to climb for a long
Generally, performance issues will result from several enough period for the wheel to clear the rail). This is
causes rather than one particular cause. Possible solutions expressed as the L/V (lateral load divided by vertical load)
can be broadly divided into design or maintenance parame- ratio. As will be explained, this situation can be caused by
ters and other measures. Solutions may relieve one per- many factors.
formance issue but may create or worsen another--the Track discontinuity derailments occur where the wheel
inter-relationships between issues and solutions are very flanges are insufficiently constrained by the track. Under nor-
important. Which solutions will work or are appropriate mal conditions, this might only occur on switches and cross-
will depend on specific vehicle and track design features and ings where there are gaps in the rails or irregularities in the
other characteristics of the transit system concerned. Solving rail contact surfaces or where moving parts may not be in
performance issues is complex, and general solutions will not their proper positions.
always be effective. The flange climbing derailment risk of IRWs will be slightly
Table 3-1 summarizes the measures identified in this higher than for conventional wheelsets because of the
research as appropriate for solving the main performance increased lateral forces, the possibility of a higher angle of
issues specified. The table distinguishes between types of attack generated by IRWs, and the configuration of LFLRV
solution in both the "parameters or other" classification and being studied. Trucks with IRW center trucks are, therefore,
by type (i.e., vehicle, wheel profile, track and switches). This fundamentally more susceptible to derailment and, as a
table illustrates the complexity of the inter-relationships result, their behavior can be strongly influenced by other fac-
involved. tors, which would normally be of only secondary importance
Sections 3.2 through 3.5 of this chapter discuss each of for trucks with solid axles.
the main performance issues in turn. Information is given Vehicle suppliers should allow for this behavior. Increased
about the extent to which these issues have actually "sensitivity" may also mean that track standards have to be
occurred in the United States and the types of vehicle and tighter than might be acceptable with more conventional
conditions involved. The causes and potential solutions are vehicles. It is also generally recognized that the management
summarized. Section 3.6 gives more background on each of of the wheel/rail interface is even more critical.
the contributory factors, based on the findings of this
research.
3.2.2. Experience with Derailments
3.2 Derailment Of the derailments that have occurred in the United States
since this type of LFLRV was introduced and which were
3.2.1 Basic Causes
noted in questionnaire responses, only the following resulted
The two principal causes of derailment that can be man- from these interface issues:
aged through the design and maintenance of vehicles and
track are flange climbing and track discontinuity. · NJ TRANSIT Newark
Flange climbing derailments occur when the wheel Subway 3 derailments All on switches.
flange climbs up out of the rails (i.e., when the vertical · MBTA Boston 11 derailments 4 on switches.
