This #Engineering Documentary details the design and construction of the one of the boldest engineering challenge undertaken. The Channel Tunnel is a 50 km rail link running beneath the English Channel, connecting The UK and France at Folkestone, Kent and Coquelles, Pas-de-Calais respectively.The tunnel began construction in 1988 with the tunnel being dug simultaneously from France and Britain with 11 massive Tunnel Boring Machines (TBM’s). Approximately 20 million passengers are ferried through the tunnel every year with a travel time of about 35 minutes.Tunnelling was a major engineering challenge, it being the second such project in the world to be undertaken after the undersea Seikan Tunnel in Japan. Due to the pressure from the sea above, a serious water inflow risk to the tunnel existed. Also being privately funded, the tunnel was under tremendous time constraint since early return of investment was paramount.The tunnel project operational model was known as a build-own-operate-transfer (BOOT) project with a concession. BOOT projects typically involve significant design and construction as well as long term operations. TransManche Link (TML) would design and build the tunnel, but financing was through a separate legal entity, Eurotunnel. Eurotunnel acquired Channel Tunnel Group (CTG) and France Manche (FM) and signed a construction contract with TML, but the French and British governments controlled the engineering and safety aspects, now being the responsibility of the Channel Tunnel Safety Authority. The British and French governments gave Eurotunnel a 55-year operating concession (from 1987 to 2052) in order to repay loans and pay dividends. A Railway Usage Agreement guaranteeing future revenue was signed between British Rail , Eurotunnel, and SNCF in exchange for the railways obtaining half of the tunnel's capacity.Power is delivered to the locomotives via an overhead line at 25 kV 50 Hz. All tunnel services run on electricity, shared equally from English and French sources. There are two sub-stations fed at 400 kV at each terminal, but in an emergency the tunnel's lighting (about 20,000 light fittings) and plant can be powered solely from either England or France.The project was not without incident however, with ten workers being killed, eight of them British, most in the first few months of construction. There were also fire incidents breaking out in the years 1996, 2006, 2008, 2012 and 2015.Despite all these challenges and budget overruns, the Channel Tunnel was finally completed in 1994 at a cost of $8.4 billion from the original planned $4.7 billion. The completed project was opened by Queen Elizabeth II and French President François Mitterrand on May 6 1994.