Discussion: “Freight Car Dynamics Session of the 1968 Joint ASME-IEEE Railroad Conference” (Liepens, A. A., 1968, J. Eng. Ind., 90, pp. 701–706, and Diboll, Jr., W. B., and Bieniecki, H. S., 1968, J. Eng. Ind., 90, pp. 708–715, and Wiebe, D., 1968, J. Eng. Ind., 90, pp. 727–735, and Henderson, K. A., and Johnson, J., 1968, J. Eng. Ind., 90, pp. 717–724)