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[quote]QUOTE: Originally posted by ironken [As far as effeciency goes, trains have trucks beat hands down. Consider horsepower per ton. A figure that is very important to the RR. We often run as little as 1 HPT on the flatter runs. Correct me if I'm wrong, but, aren't the newer semis pushing 500 hp? and hauling around 50 tons? If so that equates to 10 hpt to move that freight. Our most powered up trains on steep grades rarely use even half of that. Food for thought. [/quote] That's not really comparable. Is this truck HP's on the engine shaft? With or without parasitic loads (air conditioning, cooling etc)? Assume it is 500 hp without parasitic loads. Now: typical gear has efficency about 0.97. Count: clutch (0.97) - gearbox (0.97) - cardan shaft (2*0.97) - differential (2*0.97) - cardan shaft (2*0.97) - wheels total efficency - 0.78. Total of 390 hps actually reaches the wheels. But 0.78 is much less actually since we assimed perfect rigidity of the system (no twisting shafts etc) and perfect lubing. In reality it is probably about 0.7 so from 500 hps actually 350 finds it place on the road. But note - rubber while getting better grip, also gets higher rolling resistance - about twice of steel wheel on steel rail. So 350 truck hps is reduced to 175 'railroad' equivalent. Or 4.375 hppt. That is a value of a hot intermodal last I heard. But - trains - especially uniform unit ones - get also much lower aerodynamic drag - since each car rides in aerodynamic shadow of the car before it. Each truck must fight its way against the air by itsself. This further reduces effective the hppt for trucks. 500 hp 40 ton truck is no different then 11500 hp (three sd70m) with 4500-5000 tons trailing.
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