ARK were contracted to undertake legacy signalling design modifications to Rickmansworth Station to facilitate the introduction of longer ‘S’ Stock trains. This involved the re-location of numerous signals, trainstops and track circuit boundaries as well as the introduction of bespoke circuitry to enable the positioning of Fibre Optic Shunt Signals onto Gantry structures. ARK were the first Designers to implement Fibre Optic shunt Signals on gantry structures on the Sub-Surface Railway.