Locomotive multibody simulations are commonly used as a cost-effective tool to study, energy efficiency, wheel-rail wear, rolling contact fatigue, etc. The accuracy of the wheel-rail contact forces from multibody simulations depends on the correct modelling of the friction conditions. The friction coefficient is a function of the slip velocity, and it is influenced by several tribological parameters including, for example, material mechanical properties, environmental conditions and the presence of third body layers that vary spatially and temporally along the track. In most cases, generic friction-slip curves obtained from publications and public reports are used as inputs to the wheel-rail contact model in the locomotive simulations, as direct friction measurements using full-scale experimental set-ups are generally cost-prohibitive. A pathway to produce friction-slip curves from tribo-machine friction measurements is proposed in this paper. The pathway involves manufacturing discs from actual wheel and rail material samples to measure the traction coefficient at a spectrum of slip set points using a twin-disc tribo-machine. The tribo-machine results are scaled to be used in a locomotive multibody model that uses the modified Fastsim and a traction system co-simulation approach. Two friction curves for wet and dry conditions are processed and exemplified in a dynamic model.