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

Preceding sections have examined the relationships required to ob-
tain V f' i.e., the tractive-effort and drag-force functions. Since
D is assumed known for any given trip, the trip time would be deter-
mined from Equation (5.29) were it not for delays.
In reality, for a given level of traffic, there is a dispersion
of trip times about an average, and the average itself increases as
traffic congestion rises. Since thc variations in conditions af-
fecting trip time are largely random--being primarily speed varia-
tions due to weather, individual engine efficiency, and operator pro-
cedures--the plot of the relative frequencies of vehicles against
trip time has been approximated by a normal distribution. 14
While, for a given level of traffic, the delay time is distrib-
uted about a mean delay, the average delay itself is a function of
the level of traffic. In railroad parlance, "interference time"
increases as more trains operate on the same route. This interfer-
ence time is primarily due to trains pulling into sidings to allow
on-coming trains to pass, but it may also result from trains being
retarded behind more slowly moving units.
These ideas have been incorporated into an analysis of line-
haul delays. 15. The following trip-time expression is postulated:
T t = T f +
where T t = road time, in hours '
T f = minimum road time, in hours
5 = delay factor, in hours per train
(5.31)
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