I ADMIT to being unfamiliar with the geography of the area in question, but could a clue to a possible need for a tunnel (Mysterious Tunnel Facts Revealed March 14) be in the article – the siding for the Severn and Wye Railway?

While a bridge might be the more appropriate option if it were just a crossing point, if the siding had multiple tracks or needed width for access for loading and unloading, a tunnel would be the better choice.

– Richard Wooller, Bream.