Minimizing the energy consumption of trains brings large benefits to the railway operator. In this paper we propose an implementation concept for constrained energy optimal control of trains. In particular we exploit the structure of the pre-computed optimal control law which takes the form of a series of look-up tables for distinct destination station reaching times and train masses. Based on the currently estimated train mass and required time to reach the destination station, the correct look-up table is selected in the railway operator management centre thus ensuring evalution of the optimal train traction force based on the current train velocity and traversed path. The resulting optimal value of the train traction force is communicated to the train and either directly autonomously implemented or suggested for implementation to the driver via a driver-assistance system.