[2] On April 29, 1965, the Canadian National Railway (CNR) publicly announced that it would undertake a CAD$27 million dollar infrastructure expansion project in the Greater Vancouver area to handle new, out-of-province customers planning to use shipping terminals on the North Shore of the Burrard Inlet.
In addition, construction would include a new CAD$8.5 million, single-track railway bridge over the Burrard Inlet, and a CAD$10 million, 3.2-kilometre (2 mi), north-south single-track railway tunnel in Northeast Vancouver from the new bridge to near the Lougheed Highway to connect directly with CNR's main line track.
This change reduced the route length between the Fraser River Bridge and the Second Narrows Bridge by 11 kilometres (7 mi), most of which was along congested tracks owned by other railroads, and it would avoid CNR's rail yard near downtown Vancouver.
[13] The tunnel is named after Sir Henry Worth Thornton, who was an early president of CNR.
[15] In the middle of the tunnel there is a fake house to cover up a ventilation shaft and fan systems to blend in a residential neighbourhood.