In-line hardening of railroad rails to produce a very fine pearlite microstructure has become a commercial reality. A question that this report seeks to answer is whether or not it is possible to find an alloy composition that will permit the development of lower bainite microstructures by in-line hardening in rails, wheels, and tank car plate. The application of the in-line hardening process becomes more difficult in the production of lower bainite microstructures because of the need to quench in a controlled fashion to lower "isothermal" transformation temperatures. Use of the computer program SteCalTM has suggested that the addition of molybdenum with boron will achieve the needed development of a bainite nose accompanied by suppression of the pearlite transformation. This approach appears to be applicable to rails and tank car plates. It is not clear, however, that wheels, which can undergo rapid heating and quenching during extreme service braking, would benefit from the same approach.