Q2 Z2,(Q2) Z2(Q2) - Institute for Water Resources - U.S. Army

into segments with respect to these variables. For example, suppose
a train is engaged in a trip of length ten miles of which the first
two-mile stretch has an upgrade of 2 percent, the next two miles a
downgrade of 1 percent, and the remaining six miles are on level
ground. The trip would consist of three segments over which the
spved and, therefore, the ton-miles per hour generated by the train
would be different. The trip may be further segmented with respect
to curvature since the length and degree of each curve encountered
can be determined. Of course, the two factors of curvature and
grade will be combined on several segments, e.g., a half-mile curve
of two degrees may occur on a 1 percent grade.
Another factor that must be considered in the rail linehaul
process function is the speed limit. Any existing speed limit must
be added as a constraint to the function. For example, the analysis
may indicate a feasible speed of 100 miles per hour, whereas the
speed limit is 75 miles per hour. Again, the route may be segmented
into sections over which the speed limit constraint is operative and
over which it is not.
In the process function, time spent delayed en route is repre-
sented by T s . It was convenient to disaggregate delay time into
several components for the tow analysis. However, in the case of
rail all delays en route could perhaps be treated as one. Delay
time due to acceleration and deceleration will also be examined, be-
low. If these delays are found to be large relative to total trip
time, then they may be integrated into the rail process function
by using forms of the function which include acceleration and
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