Canal Tunnels

Approximately 0 miles 63 chains (0.79 miles, 1.27 km) down the line from the divergence of the Canal Tunnel lines, the Holloway flyover carries the Up Slow track over the two fast tracks of the East Coast Main Line (ECML). This converts the ECML from being quadrupled by direction to being quadrupled by speed,^[a] which means the Canal Tunnel lines can separate without crossing the fast tracks.^[3]: 204

The tracks for the Canal Tunnels then separate from the ECML at Belle Isle Junction, on a flat junction with lines E and F, which change name from Down Slow and Up Slow at this point before entering the Gasworks Tunnel into London King's Cross 0 miles 11 chains (0.14 miles, 0.22 km) later. The diverging tracks for the tunnel are called the Down Canal Tunnel and Up Canal Tunnel tracks, and they have a speed limit of 30 miles per hour (48 km/h), including on the points of Belle Isle Junction.^{[3]: 203–204}

Having diverged from the ECML, there is then a facing point at the first junction named Canal Tunnel Junction, which is partially submerged in the start of the tunnel. Immediately after this point is the boundary between the Eastern region and the East Midlands region of Network Rail. The two tracks then split to allow the Down Moorgate and Up Moorgate lines to come in between from underneath. These lines come from the Midland Main Line at Kentish Town railway station.^{[3]: 464–466 [b]} The two sets of tracks then merge at Canal Tunnels Junction immediately to the north of the subsurface platforms at St Pancras railway station, lettered A and B.^[3]: 464

Power is normally from supplies for the nearby Midland Main Line however provisions to use those of the ECML were made.^[2] For safety reasons, emergency service radio systems have been installed, along with a walkway and automated LED lighting at four-metre intervals for an escape route for any passenger evacuation of the tunnel. On account of the Regent's Canal being above, flood management measures were built, including a drainage system with a large sump beneath the tunnel, which is pumped into the ECML's drainage system.^[2][1] The infrastructure has bi-directional working for greater operational flexibility.^[5][2]

v t e King's Cross & St Pancras approaches
Legend
ECML & Thameslink to Finsbury Park Midland ML & Thameslink to Kentish Town Copenhagen Tunnel Copenhagen Junction North London line to Gospel Oak North London line to Highbury & Islington High Speed 1 to Stratford International Regent's Canal Canal Tunnels Gasworks Tunnel St Pancras King's Cross Thameslink to Blackfriars

The Canal Tunnels were constructed as part of the wider Thameslink Programme, a £6 billion project to upgrade and expand the north–south railway crossing the capital. They were the first main section of Thameslink to commence construction.^[2][5] Their main purpose is to link the East Coast Main Line (ECML) with the Thameslink network; a junction connecting the tunnel's northern approach to the ECML is 100 m (330 ft) from the northern portals.^[2][5]

The tunnels were designed by Halcrow Group, part of the Rail Link Engineering consortium. The construction process itself took roughly two years, with civil works commencing in 2004 and completed in 2006. Design and construction of the tunnels were planned to integrate with the adjacent railway engineering works for High Speed 1 and the redevelopment of the Railway Lands and St Pancras railway station.^[1][5] The tunnels were driven using tunnel boring machines (TBMs). Each bore is 6 m (20 ft) in diameter and lined with pre-cast concrete segmental rings. The northbound tunnel is 860 m (2,820 ft) long, while the southbound tunnel is 820 m (2,690 ft) long; the disparity is due to curvature.^[2] The tunnels have a maximal incline of 1 in 34; the nadir is next to the main sump system.^[1][6]

Despite their problem-free completion, the Canal Tunnels remained unused for several years. This was largely due to being completed well in advance of numerous other Thameslink elements, such as delivery of the new British Rail Class 700 multiple units ordered for the service and other infrastructure works.^[1][5] During this interval, track, power supply, and signalling systems were installed. In August 2012, railway infrastructure owner Network Rail announced that the construction company Carillion had been appointed as the principal contractor for the fitting-out of the Canal Tunnels.^[1]

The fitting-out process commenced during 2013 and was completed during the following year, several years ahead of services running; this was reportedly to facilitate stock movements and to take advantage of available land to facilitate the work.^[5] The signalling systems installed were integrated with Thameslink's High Capacity Infrastructure; in addition to conventional colour light signalling, the European Train Control System is present; Thameslink officials claimed that this arrangement was the world's first implementation of such technology on a mainline 'heavy' railway.^[2] Wherever possible all wiring, mechanical, and electrical equipment was cleanly run in a pair of interior troughs. Amongst the last elements of the work was the connection of the new track to the existing lines with new junctions.^[1][7]

External media
The northbound entrance to the tunnel showing the trailing point
A cab ride through the Canal Tunnel southbound

On 26 February 2018, the first passenger service traversed the Canal Tunnels after many out-of-service trains had done so for testing.^[2][8] The tunnels were officially opened to traffic during May 2018, forming a part of the Thameslink route from that month onwards.^[5] Until then, capacity in the Thameslink Core had been limited to 16 trains per hour from the Midland Main Line, but the addition of ECML trains added another 8 trains of capacity. This meant the hypothetically possible peak service capacity was 24 trains per hour between St Pancras and Blackfriars, though as of 2024, this frequency has never been reached.^[2][9] Many of these movements are automated, making use of the route's advanced digital signalling.^[2]