The Wheel-rail adhesion is essential for safe and stable vehicle operation. Since the beginning of railway construction, many railway researchers and engineers have been actively involved in the study of this railway-specific issue. Most studies to date have focused on the various factors influencing the adhesion characteristics and quantifying the extent of their influence. This paper gives an overview of experimental and theoretical studies on evaluating wheel-rail adhesion characteristics under conditions where different third-body materials are interposed between wheel and rail and describes further challenges and research directions in the field of adhesion for the future. •The influences of various contaminations between wheel and rail have been assessed.•Third-body material has a significant influence on the wheel/rail adhesion coefficient.•The adhesion coefficient decreases in the order of dry, wet, oil, wet leaf, and dry leaf.•Alumina particles, sand, and traction gel have the effect of increasing adhesion.