The Detroit–Windsor tunnel (), also known as the Detroit–Canada tunnel, is an international highway tunnel connecting the cities of Detroit, Michigan, United States and Windsor, Ontario, Canada. It is the second-busiest crossing between the United States and Canada, the first being the Ambassador Bridge, which also connects the two cities, which are situated on the Detroit River. History Construction The Detroit–Windsor tunnel was built by the firm Parsons, Klapp, Brinckerhoff and Douglas (the same firm that built the Holland Tunnel). The executive engineer was Burnside A. Value, the engineer of design was Norwegian-American engineer Søren Anton Thoresen, while fellow Norwegian-American Ole Singstad consulted, and designed the ventilation. The method used to construct the tunnel was immersed tube (sections of steel tube floated into place and sunk into a trench dug in the river bottom), as was done in the earlier Posey Tube. The tunnel sections have three main levels. The bottom level brings in fresh air under pressure, which is forced into the mid level, where the traffic lanes are located. The ventilation systems forces vehicle exhaust into the third level, which is then vented at each end of the tunnel. The total cost of construction was approximately $25 million (around $ in dollars). The river section of the tunnel was connected to bored tunnels on both banks. The tubes were then covered over in the trench by of mud. Because the tunnel essentially sits on the river bottom, there is a wide no-anchor zone enforced on river traffic. The tunnel is short of a mile at . At its lowest point, the two-lane roadway is below the river surface. Completion in 1930 The Detroit–Windsor tunnel was completed in 1930. It was the third underwater vehicular tunnel constructed in the United States, following the Holland Tunnel, between Jersey City, New Jersey, and downtown Manhattan, New York, and the Posey Tube, between Oakland and Alameda, California. Its creation followed the opening of cross-border rail freight tunnels including the St. Clair Tunnel between Port Huron, Michigan, and Sarnia, Ontario, in 1891 and the Michigan Central Railway Tunnel between Detroit and Windsor in 1910. The cities of Detroit and Windsor hold the distinction of jointly creating both the second and third tunnels between two nations in the world. The Detroit–Windsor tunnel is the world's third tunnel between two nations, and the first international vehicle tunnel. The Michigan Central Railway Tunnel, also under the