The second tunnel was built to handle intermodal rail cars with double-stacked shipping containers, which could not fit through the original tunnel or the Michigan Central Railway Tunnel in Detroit.
By the early 1990s, CN had commissioned engineering studies for a replacement tunnel to be built adjacent to the existing St. Clair River tunnel.
In 1992, new CN president Paul Tellier foresaw that CN would increase its traffic in the Toronto–Chicago corridor.
The Canada-U.S. Free Trade Agreement was implemented in 1989 and discussions for a North American Free Trade Agreement between Canada, the United States and Mexico discussions were underway at that time (NAFTA was implemented in 1994).
It was only logical that import/export traffic on CN's corridor would increase dramatically.

In 1993, CN began construction of the newer and larger tunnel.
Tellier declared at the ceremonies:
"[the] tunnel will give CN the efficiencies it needs to become a strong competitive force in North American transportation"
Unlike the first tunnel, which was hand dug from both ends, an earth boring machine called the Excalibore made by the Lovat Tunnel Equipment Inc. was used.
It started on the Canadian side and dug its way to the U.S.
The tunnel opened later in 1994 whereupon freight and passenger trains stopped using the adjacent original tunnel, whose bore was sealed.
The new tunnel was dedicated on May 5, 1995 and measures 6,129 feet (1,868 m) from portal to portal with a bore diameter of 27 feet 6 inches (8.38 m) with a single standard gauge track.
It could accommodate all freight cars currently in service in North America, thus the rail ferries were also retired in 1994 at the time of the tunnel's completion and opening for service.

On November 30, 2004, CN announced that the new St. Clair River tunnel would be named the Paul M. Tellier Tunnel in honour of the company's retired president, Paul Tellier, who foresaw the impact the tunnel would have on CN's eastern freight corridor.
A sign now hangs over each tunnel portal with this name.
The second tunnel was built to handle intermodal rail cars with double-stacked shipping containers, which could not fit through the original tunnel or the Michigan Central Railway Tunnel in Detroit. By the early 1990s, CN had commissioned engineering studies for a replacement tunnel to be built adjacent to the existing St. Clair River tunnel. In 1992, new CN president Paul Tellier foresaw that CN would increase its traffic in the Toronto–Chicago corridor. The Canada-U.S. Free Trade Agreement was implemented in 1989 and discussions for a North American Free Trade Agreement between Canada, the United States and Mexico discussions were underway at that time (NAFTA was implemented in 1994). It was only logical that import/export traffic on CN's corridor would increase dramatically.
In 1993, CN began construction of the newer and larger tunnel. Tellier declared at the ceremonies:
"[the] tunnel will give CN the efficiencies it needs to become a strong competitive force in North American transportation"
Unlike the first tunnel, which was hand dug from both ends, an earth boring machine called the Excalibore made by the Lovat Tunnel Equipment Inc. was used. It started on the Canadian side and dug its way to the U.S.
The tunnel opened later in 1994 whereupon freight and passenger trains stopped using the adjacent original tunnel, whose bore was sealed. The new tunnel was dedicated on May 5, 1995 and measures 6,129 feet (1,868 m) from portal to portal with a bore diameter of 27 feet 6 inches (8.38 m) with a single standard gauge track. It could accommodate all freight cars currently in service in North America, thus the rail ferries were also retired in 1994 at the time of the tunnel's completion and opening for service.
On November 30, 2004, CN announced that the new St. Clair River tunnel would be named the Paul M. Tellier Tunnel in honour of the company's retired president, Paul Tellier, who foresaw the impact the tunnel would have on CN's eastern freight corridor. A sign now hangs over each tunnel portal with this name.
St. Clair Tunnel