California State Rail Plan 2005-06 to 2015-16

2005-06 – 2015-16 California State Rail Plan
effort. The typical large DC locomotive attains about 30 percent adhesion on dry
rails, while AC locomotives attain up to 38 percent adhesion in varied weather
conditions. The upper limits of AC locomotive adhesion are still to be
determined, but some engineers believe 50 percent is a practical number.
The greater simplicity of AC traction motors reduces the potential for down time.
The AC traction motors have the ability to withstand higher thermal loads, and
thus can operate a greater length of time under a heavy load before overheating.
ELECTRONIC BRAKING
For over a century, US railroads have used the air brake technology developed in
the late 1870s. The system employs air pressure changes controlled from the
locomotive and extending through a continuous air line running the length of the
train, to apply and release the brakes on the individual cars. With the advance of
electronics, several versions of electro-pneumatic braking systems have been
developed and are currently being tested. Electronic braking uses electronic
signals to control and operate brake valves simultaneously, whereas the standard
system has a lag time as the air pressure changes sequentially throughout the train.
Use of the new technology has centered on unit trains, where all the cars have the
new system. However, several systems under development can operate with
electronically-equipped cars intermixed with cars having traditional air brakes,
allowing for gradual replacement of braking systems on existing cars. Electronic
braking has numerous advantages, including shorter stopping distances, reduced
wheel wear, and fewer mechanically related train delays. The electronic approach
also allows systems to incorporate diagnostic sensing and other reporting of train
operating information. With over a million freight cars in interchange service
today, it is estimated that it will take over ten years before the entire car fleet can
be equipped with this technology.
INCREASED CAR CAPACITY
Larger freight cars capable of carrying heavier loads are a technological
improvement with mixed blessings. Larger cars have potential for transportation
savings, but they also require heavier, better-engineered and maintained track and
structures (bridges, trestles, etc.) to withstand the greater forces applied to the
track. This is a particular problem for many short lines that have infrastructure
that is unable to accommodate the heavier cars, as described previously.
Heavier-weight cars reduce car movements for the railroads that have the track
structure able to handle them. There are indications that the industry is moving
toward even greater weights per carload with cars capable of up to
315,000 pounds.
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