The Louis-Hippolyte Lafontaine Bridge–Tunnel (French: Pont-Tunnel Louis-Hippolyte-La Fontaine) is a highway bridge–tunnel running over and beneath the Saint Lawrence River.

It surfaces on Île Charron (Îles de Boucherville at Exit 1 of Autoroute 25), then continues by bridge to Longueuil.

[2][3] In 1960, the construction of the Trans-Canada Highway (TCH) through Quebec from the Ontario border to Rivière-du-Loup was announced.

[5] A major four-year refurbishment of the tunnel began in 2020 was originally planned to be completed in 2024 at a cost of $1.2 billion, but in 2022, it was announced that the project would take a year longer than expected and that at its completion in 2025, it will have a total cost of $2.1 billion.

The tunnel was built with sections prefabricated in dry dock and then sunk in the river[7] 24 metres (79 ft) below the surface of the water.