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[quote]QUOTE: <i>Originally posted by Kevin C. Smith</i> <br /><br />If I may weigh in with a slightly off-topic question here... <br />In articles about WWII traffic densities, mention is always made of CTC as a godsend to RR's that needed increased line capacity quickly. The assertion was made that CTC gave a single track line 90% of the capacity of double track. With the major main lines already CTC'd and double track being laid as fast as $$ will permit, I've wondered if all this time and money is just to get that last 10%-yet isn't the Abo Canyon project on BNSF supposed to increase the number of trains by 30-50% (if I'm way off, lemme know-when it comes to numbers, I EASILY get my wires crossed). So, the big questions are: Is the 90% capacity claim still valid? If not, why not? (Longer trains? More uniform traffic mix-no locals to limiteds variety to deal with? Fewer helper districts?) <br /> <br />Was it really ever true-or just advertising? <br />[/quote] <br />The 90% figure is not unreasonable if you understand the characteristics of railways of that era. Double-track is by definition one-way, not reverse-signalled, and usually had few crossovers and hand-throw at that. Operating plans had to work around passenger trains which ran on fixed schedules that were often dreadfully inconvenient from a capacity-optimisation perspective, coupled with wayfreights and plodding drag freights that got in everythjing's way. <br /> <br />What CTC really gave the railway of the 1930s and 40s was an immense reduction in operating costs. Track maintenance is very expensive, and while if you quit running trains on the second track you do save on rail wear, the ties still rot, the culverts still plug, and the surfacing still goes to hell every spring if your drainage isn't good. Plus, it eliminated the operator every place you wanted to meet trains or do a runaround, and the expense of five men (three shifts, seven days, plus vacation and sick relief) for every station, multiplied by hundreds of stations, was breathtaking. <br /> <br />Track capacity isn't hard to quantify under any number of conceivable track, signaling, and train speed and length configurations. The subject was exhaustively reduced to formulae in the 1920s and the limitations of each configuration was well understood. One factor rarely understood outside the biz is that you have to allow time for maintenance windows. Once traffic gets past a certain level on single-track lines it can almost seem as if you're constructing the second main track just so the gangs can get out on the first one and get something done. The point is that capacity is idiosyncratic and what works for one railway in one place can't be compared to another in another place without understanding the traffic and geographic characteristics of each. <br /> <br />S. Hadid
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