A 154-page report by Moreu and LaFave in 2012 explains unique problems railroad bridge engineers must contend with. The gross weight of cars went from 200,000 pounds to 263,000 pounds in the 1970s, and to 286,000 pounds in 1991. The ratio of live to dead loads are much greater for railroads than highways. Dynamic forces due to such things as wheel hunting, rock and roll, locomotive tractive forces, and braking make it very desirable to measure motions in all three directions (i.e., longitudinal, transverse, and vertical directions), which is why a survey of railroad bridge engineers ranked measuring 3D deflections under live loads as the top research interest.

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