 The Department for Transport HS2 report of the same date recommended that, if a direct rail link is built, it should be the classic-speed, double-track option.This route proposal was supported by Arup's final report in December 2010, which concluded the best option would be to construct a tunnel between Old Oak Common and Chalk Farm, and then to use existing widened lines along the North London Line to connect to HS1 north of St Pancras.The proposed connection would be built to GC loading gauge and would not be suitable for trains running at high speed.