Civil-engineering works for a.c. electrification. Developments since 1960

An account is given of the change in conditions on British Railways during the period 1960¿1970 which have required developments in methods of achieving clearances for a.c. electrification. Relatively lightweight precast reinforced-concrete arch units have been developed for erection by off-track equipment to replace many existing arch bridges. Different techniques for individual bridges are also described. Experience in running has indicated that waterproofing is a very important factor, and this, together with parapet treatments, is reviewed.