Canadian authorities tried to reassure the public about the safety of bridges in the country following the collapse of a bridge in Baltimore, Md., early Tuesday morning after it was rammed by a container ship.

Halifax Harbour Bridges, which operates the two spans across the harbour between Halifax and Dartmouth, said it has taken steps to mitigate the risks of collisions between ships and bridges. The Crown corporation says it is notified by the port authority every time a commercial vessel is scheduled to pass underneath the spans.

害羞草研究所淏ridge patrol staff provide physical lookouts on the bridges as ships pass, and a complex series of cameras monitor and record the transit,害羞草研究所� the corporation said in a news release.

As well, rock islands built around the piers of the bridges in 1983 offer further protection, Halifax Harbour Bridges said.

Rock islands or other protective structures appear to have been missing from the piers of Francis Scott Key Bridge in Baltimore, said Bruno Massicotte, an engineering professor at Polytechnique Montr茅al.

The bridge was struck around 1:30 a.m. by a container ship that lost power and rammed into one of the piers, sending vehicles plunging into the water. Six people are missing and presumed dead.

Massicotte said he is surprised that the bridge害羞草研究所檚 piers weren害羞草研究所檛 protected to absorb the energy from a possible ship strike.

害羞草研究所淲hen you have a bridge pier in the waterway, it has to be protected against ship impacts,害羞草研究所� Massicotte said in an interview Tuesday.

The easiest way to do that is to surround a pier with concrete, steel or rocks, which can all absorb the energy from a potential strike and block a vessel from hitting the bridge itself, he said. Canada害羞草研究所檚 bridge code requires piers to be similarly protected if they are considered to be vulnerable to ship strikes.

害羞草研究所淎 bridge pier is not designed to resist that kind of impact, so that害羞草研究所檚 why we put things in the water,害羞草研究所� he said.

Quebec害羞草研究所檚 Transport Department, which is responsible for several bridges spanning the St. Lawrence River, said it has protected the piers of the only bridge under its jurisdiction that has been judged at risk of being struck by commercial ships.

That bridge, the Laviolette Bridge connecting Trois-Rivi猫res, Que., to B茅cancour, Que., is built from the same material as the span that collapsed in Baltimore, department spokesman Louis-Andr茅 Bertrand said in an email.

In 1986, Bertrand said, the department conducted 害羞草研究所渕assive害羞草研究所� work to create protective islands around the bridge害羞草研究所檚 piers.

害羞草研究所淎s a result, if a ship approaches one of the foundation units, it will be stopped by the granular material around the pier and will not be able to reach it,害羞草研究所� he wrote, adding that in 1992 a boat ran aground near the bridge without causing any damage to the structure.

Most other large bridges over the St. Lawrence River don害羞草研究所檛 have piers located in shipping lanes, he said.

In British Columbia, the Ministry of Transportation and Infrastructure said plans are in the design stage to protect the Lions Gate Bridge and Ironworkers Memorial Bridge, both of which connect Vancouver to neighbouring suburbs, from ship collisions.

害羞草研究所淲e are enhancing the existing concrete collar at the base of the south tower of the Lions Gate Bridge with an in-water rock-fill berm,害羞草研究所� the ministry said in an emailed statement. 害羞草研究所淭he north tower already has one. We will also be installing in-water deflection structures at the Ironworkers Memorial Bridge.害羞草研究所�

Elena Dragomirescu, an engineering professor at the University of Ottawa, said any bridge, regardless of its age, could collapse if it is struck by a large cargo ship. 害羞草研究所淏ridges need all the components to work together. If one of the components is damaged, or collapsed in this case, then the entire bridge is at risk,害羞草研究所� she said in an interview Tuesday.

But it is rare that bridges collapse because they are struck by ships, she said. Dragomirescu said she害羞草研究所檚 more worried about the structural integrity of decaying spans across Canada that could come down because of poor maintenance 害羞草研究所� like in 2006 in Laval, Que., when a highway overpass collapsed and killed five people.