Attenuation effects of under-track reinforcing on automatic train protection signalling systems

The aggregate of steel reinforcement in the concrete plinths and track bed of a particular masstransit railway is found topresent an attenuating environment to the ATP (automatic train protection) signalling system. An attempt is made to investigate the problem via two-dimensional field theory by solving Laplace´s equation for the magnetic vector potential. The distributed AC parameters of the secondary circuits formed unintentionally near the track are established. The attenuation of the ATP signals in the presence of steel reinforcement is evaluated for various conditions and is found to be in good agreement with measurements carried out with life-size circuits.