HOW OTHER CITIES HANDLED HIGHWAY TUNNELS

Seattle

When work on a three-kilometre highway tunnel began in 2013, it was projected that cars would be zipping through it by the end of this year. But Bertha, the world’s largest tunnel boring machine, broke down and crews spent much of 2014 trying to raise, then repair, its 2,000-pound cutting head. Bertha is scheduled to resume digging again in November. The tunnel completion estimate was recently revised to 2018, and critics are concerned about cost overruns. Boston

The Central Artery/Tunnel Project, known as the Big Dig, buried an aging, expensive elevated highway that ran though the heart of Beantown. The project ended up becoming one of the most expensive schemes in U.S. history, costing $15 billion, more than 10 times the estimate. Scheduled to be completed in 1998, it opened almost a decade later. The Big Dig has spooked tunneling projects all over the world, and opinions are divided on its long-term success. Montreal

The Ville-Marie Expressway, running east and west below downtown Montreal, opened in the mid-1970s. About 100,000 vehicles use the highway on an average weekday, compared to the 110,000 to 200,000 motorists travelling on the Gardiner. In 2011, a huge concrete slab fell across four lanes of the Ville-Marie Expressway. No one was injured but the incident was one of a series of incidents pointing to the city’s crumbling infrastructure.