Preparations are underway for a $200-million revamp of the Angus L. Macdonald Bridge in 2015.

The construction project means the 57-year-old bridge will be closed from 7 p.m. to 5 a.m., and closed to walkers and cyclists for at least 18 months.

It's the Halifax Harbour Bridges' (HHB) biggest construction project since the A. Murray MacKay Bridge was built in 1970.

The HHB plans to completely replace the trusses and decking of the span on the Macdonald Bridge, section by section.

"We'll be replacing everything that's underneath people. The only thing that'll be left once we're done on a suspended span is the orange main cables and the green towers," said Jon Eppell, senior engineer for HHB.

The work will be done in the evenings and overnight to allow commuters to use the bridge during the day.

This construction method has only been done once before — for the Lion's Gate Bridge in Vancouver.

But to lighten the load on the bridge for safety reasons, the sidewalks for pedestrians and bicycles have to be removed.

The chair of Halifax's Active Transportation Committee says if that's the case, then the commission should do something to make up for the inconvenience.

"We look at making that entrance way to the bridge much more accessible, much more bike-friendly," says Coun. Jennifer Watts.

Since the project won't start for two and a half years, there is time for public consultation. The commission says its open to other ideas for pedestrians and cyclists.

Drivers make 36 million trips a year over the bridges, according to the HHB.