Further, with the advancement of technology and changing train operation, more demand has been placed on higher adhesion levels to support higher braking rates, shorter yet faster trains and more frequent services. The nature of the difficulty encountered depends on a vast range of factors which change constantly.
The ‘adhesion profile’ along any stretch of line varies within metres: the temperature and humidity levels can change rapidly; contaminants react differently to the passage of a train; the trains are driven differently; the trains themselves are different, and so on.
Low adhesion occurs all year round, not just in the autumn. Wet rails, accompanied by rail-borne contaminants, can offer low adhesion levels despite the rails looking clean. Analyses have shown as many station overrun incidents due to poor rail conditions can occur outside of the autumn period as during it.