As MacKay Bridge nears end of its lifespan, N.S. eyes replacement or repair

Halifax's A. Murray MacKay Bridge may be best known as the city's "new bridge," but rehabilitating it to modern standards, the way the Macdonald Bridge was during the Big Lift six years ago, may not be the best option.

"Critical components of the MacKay are approaching [the end of] their service life," said Tony Wright, CEO of Halifax Harbour Bridges.

"We anticipate that a major rehab or replacement project would need to be done by about 2040."

That's why Halifax Harbour Bridges will soon issue a tender for a detailed analysis comparing the costs of repairing or replacing the span, first opened on July 10, 1970.

The Crown corporation hopes to find a company to complete what Wright referred to as "essentially a 30 per cent design of what it will take to do the rehab of the MacKay."

He said, "that should give us a good understanding with credibility of the cost, scope, schedule and potential traffic interruptions during such an undertaking."

This new examination will build on the results of a feasibility study completed in 2018 by the engineering consulting firm COWI North America.

At the time, the company was asked to consider two scenarios  — extending the life of the existing structure by 75 years or building a new bridge with a 100-year lifespan. Either way, the result would include more traffic lanes than the current structure and add active transportation routes for cyclists, runners and pedestrians. 

It recommended building a new, "slightly longer" bridge."The preferred replacement option involves construction of a bridge with six traffic lanes and two active transportation lanes," noted the report. "Likely a 500-metre-long main span cable-stayed bridge, on an alignment parallel to the existing bridge along its north side.

"The existing bridge would then be demolished. This option would require some property acquisition and relocation of the Canada Food Inspection Agency building in Dartmouth adjacent to the existing bridge."

Although work continues under the deck of the Macdonald Bridge to shore up some steel components and make sure the structure is sound, the most disruptive part of its rehabilitation happened overnight and did not shut down the bridge for extended periods.

But a similar "big lift" operation on the MacKay would be much more complicated than the Macdonald's two-year-long deck replacement.

"The MacKay was built with a different standard back in the '70s," said Wright, explaining that its deck would need to be made thicker. "Macdonald for instance, the bridge is a 14-millimetre deck and current Canadian code would need to see us replace the MacKay Bridge with a 14-millimetre deck."

According to Wright, that would mean having to hang new, stronger main cables and building additional support towers before any work could begin on replacing the deck.