A tribologist's dream is to predict the point at which a lubricant film will fail. The precursor to this ideal situation is to predict the decay behaviour of a lubricant film prior to failure. The performance decay of lubricants is of interest to the rail industry for two reasons; first, to predict reapplication rates, and second, to predict the lubricated distance from a lubricant application point. The work discussed in this paper investigated the failure of lubricant films in a simulated rail curve environment. Three rail curve lubricants were tested under traction-limited rolling sliding conditions. New methods for measurement of rail curve lubricant performance were developed and one method, the half life of lubricant is discussed and results presented here. Lubricant half life in this work represents the reduction of sliding performance over time at a defined shear stress level or the time taken for a lubricant to lose half of its sliding performance. Decay of lubricant performance was measured for three different rail curve lubricants under simulated conditions. The rail/wheel simulator used in this research consists of two dissimilar wheels (disks) rotating in contact with one another, simulating a conformal gauge corner contact. The first wheel, a simulated rail, is driven by an electric motor which then drives the second wheel, a simulated railroad wheel, through the contact. Hydraulic braking on the railroad wheel is used to simulate the rolling/sliding conditions. The research found appreciable and quantifiable differences between lubricants. Industrial application of the findings will improve positioning of lubrication systems, improve choice of lubricants and predict effective lubrication distance from the lubricant application point.