The presence of a third body between the wheel and rail can significantly reduce adhesion, thereby posing serious safety challenges for railway operations. Due to the characteristics of multi–wheel trains and fixed–line operation, the continuous rolling action of multiple wheels on the same point of the rail surface can lead to a thinning of the third body layer. This study develops a numerical model of wheel–rail contact under starved lubrication conditions, integrating fluid lubrication with micro–asperity contact mechanics, to elucidate the mechanism of adhesion improvement induced by multiple–wheel rolling under wet conditions. The results indicate that successive axle passages contribute to further thinning of the water film and corresponding increases in adhesion, particularly at higher speeds and under lighter axle loads. In addition, a laboratory validation approach is proposed using a circumferential wheel–rail test rig. The experimental results corroborate the model predictions, confirming the trend of adhesion improvement through continuous multi–wheel rolling. These findings offer theoretical and experimental support for the development of braking strategies that account for adhesion variations, thereby improving braking performance and ensuring safer train operations under wet conditions.