Replacement Tunnel Lighting switching system for road Tunnels at Brynglas (M4) and Monmouth.

Light levels are controlled by a dedicated computer system and depend on exterior daylight conditions. The computer system communicates switching sequences to outstation equipment mounted at various locations in and around the tunnels.

Following problems with the outstations a new system was designed using PLCs. These provided local indication of lighting banks selected, local test facilities and future availability of spare parts. Each tunnel was modified during a scheduled road works closure lasting less than eight hours.