For many years, England and France wanted to link their two countries with a train tunnel under the English channel. This was a huge challenge for the British and French engineers. The tunnel would have to be 50 kilometres long-one of the longest in the world. But more importantly, in would have to be safe.
Since much of the tunnel would be underwater, an accident inside the tunnel could be a disaster. So the engineers built an escape route. The Tunnel is actually three tunnels side by side. Tow of the tunnel are for trains. In between these two tunnel is a smaller tunnel which is used by railway. This smaller tunnel can also be used to get people out if there is an accident.