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Copyright
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(Copyright © 1997, Transportation Research Board, National Research Council, National Academy of Sciences USA, Publisher SAGE Publishing) |
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Abstract
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This analysis presents amethodology for measuring the efficiency of train dispatching as a product of three variables: (a) the type of train control system (measured by latency, defined here as the interval between occurrence of a schedule deviation and initiation of corrective action); (b) the physical capacity of the route (track kilometers per route kilometers); and (c) train minutes per route kilometer (a measure of both capacity and dispatcher competence). A mathematical relationship among these three variables is postulated, and a log-log regression analysis is used to develop coefficients that relate each of the three independent variables to dispatching efficiency. To do this, actual train-movement data and minimum train running times for 28 U.S. Class I railroad line segments are used.
RESULTS of the regression analysis indicate a statistically valid relationship among latency, track capacity, traffic volume, and dispatching effectiveness. Dispatching effectiveness, calculated by placing track kilometers per route kilometer, train minutes per route kilometer, and latency at their mean values, was 71.3 percent (the mean latency was about 17 min). At a latency of 3.5 min, average effectiveness is 81.3 percent. Examples of the trade-off between latency and effectiveness and between track capacity and effectiveness also can be calculated. For the average line, when latency is progressively reduced from the current value of 15 min to 3.5 min, dispatching effectiveness increases from 71.3 to 81.3 percent. When track kilometers per route kilometer are increased from the average value of 1.3 to 2.0 (double-tracking the entire railroad, holding all other values constant) dispatching effectiveness can be increased from 71.3 to 89.5 percent--a larger increase than that realized from a reduction in latency, but at much higher cost. To quantify the dollar benefits of such an increase in dispatching effectiveness for U.S. railroads, further analyses were carried out. Based on a previous study of Burlington Northern operations, train delay costs ranged from $163/hr to $266/hr. To simplify calculations, a value of $200/hr is used. According to U.S. railroad statistics, there are about 21 million train hours of traffic each year. Benefits available from installing communications-based train control are calculated in terms of additional train minutes per route kilometer available with an increase in dispatching effectiveness based on this analysis. Based on this analysis, it should be possible to save (1 - 0.713/0.813) or 12.3 percent of total train hours. The benefit of this would be $200 x 0.123 x 21 x 10 or $520 million annually. The Association of American Railroads has estimated the cost of positive train control for the entire U.S. railway network to be between $843 million and $1.1 billion.
Language: en |