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Concrete ties indeed do make for a stiffer roadway, thus saving on fuel and wear (flexing) of the track. Thus they can be spaced slightly farther apart, saving a litle. I helped build the concrete tie plant in Denver, those were prestressed with 32-6mm wires. Under "normal" loads they do not go into tension. Tension will crack concrete at very low stress, so for durability you want them always in compression. The wires are tensioned and concrete placed in the forms. The concrete is steam cured to get strength by the nex morning, the prestressed wire are de-tensioned. At this point the friction between the wires holds the wires in tension, thus compressing the concrete. The crews then cut the wires, remove the completed tie whereit goes into the yard for storage. Our plant could make 1440 ties a day. <br /> <br />Back to track flexing, in the engineering world that is called pumping. On a RR it causes the fines from the soil below the ballast to work it's way up into the bassalt. When that happens you get a condition that caused the derailments in Powder River area. Then you rebuild the track secton, a barrier between the soil and ballast, ballast the ties and rail. At Powder River, the fines came from above, blowing coal dust. I haven't read anything about a planned fix for the problem.
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