The High Speed 2 railway network has been a hotly debated topic in recent months. But what about the existing system? It's believed that by the time HS2 is built, the current infrastructure will need to cope with twice as many passengers as now, so the team looks at the measures being taken to ensure the ageing system stays on track. Liz Bonnin explores the possibility that signals may disappear and how hearing impairment could be one of the bigger killers on the railway, and Maggie Philbin reveals how a train travelling at 125mph is set to revolutionise trackside maintenance