Building up effective and economical countermeasures is needed to prevent lightning damage to railway signalling systems. Therefore, we measured the wayside ground potential distribution when a rail potential rise was caused by injecting a lightning surge current into a rail. Moreover, we injected a lightning surge current into the rail or wayside ground, raising their potential in order to measure the lightning overvoltages on a level crossing so that basic insulation design data could be obtained. This paper demonstrates that an effective countermeasure is to earth lightning protective devices, which are attached to the electronic train detectors on a level crossing to suppress any lightning overvoltages.