If you've travelled along the new Port Mann bridge recently, you've probably noticed a 50-foot wide gap at the centre of the old bridge next door.

A 50 ft section at the centre of the bridge has been removed. Deconstruction continues towards both ends of the bridge. (Michelle Eliot, CBC )

The iconic orange arches of the Port Mann bridge are coming down, piece by piece, starting with the middle.

"It culminates the end of the project,"says Linda Meindersma, bridge segment manager with the Transportation Investment Corporation.

"We've built the new bridge. We're working on opening the final two lanes, and then the end of the project is removing the old bridge"

Engineer Linda Meindersma is working on deconstruction of the original Port Mann Bridge. (Michelle Eliot, CBC )

The first Port Mann Bridge opened in 1964. It was hailed as the longest arch bridge in Canada and would enable commuters to cross the Fraser River between Surrey and Coquitlam, B.C. in record time.

But eventually, traffic exceeded the capacity of the five-lane bridge. Dismantling of the bridge began in 2012.

The same year, the new 10-lane Port Mann Bridge partially opened to traffic.

Dismantling old bridge a challenge for crews

Crews are taking apart the bridge in 50-foot sections, working in reverse from when the original bridge was built, starting with the middle section and working toward both ends.

"It allows a controlled deconstruction. Every part is thought about. Every step is planned, so you know what's going to happen with the structure," says Meindersma.

The two Port Mann bridges sit in striking contrast beside each other. (Michelle Eliot, CBC )

Because the centre arch acted as the "keystone" of the bridge and supported the rest of the structure, towers are installed at opposite ends to support the remaining parts of the bridge. Cables connect the bridge deck to towers that provide a new foundation.

During dismantling, crews must consider the well-navigated and environmentally important Fraser River. Sections of the bridge are cut up and lowered onto a barge on the river below.

"In the old days, many bridges used to be imploded, so blasting would occur and then the bridge would fall into the river. The Fraser is quite an important habitat. It's environmentally protected." says Meindersma.

CBC listener Rory Filer photographed the two Port Mann bridges in December, 2012. (Rory Filer )

The new 10-lane Port Mann bridge is significantly larger than its predecessor, at 2.2 kilometres long and 65 metres wide. The towers reach 75 metres above the bridge deck. The final two lanes, including a multi-use pedestrian / bike path, are near completion.

"It's amazing to see how big the structures are we're building nowadays," says Meindersma.

"The new Port Mann bridge towers above the original bridge, which used to be very iconic and stand above the river. The new bridge dwarfs it"

Catch Michelle Eliot with On the Move, a segment on commuter issues, Tuesdays at 6:50 on The Early Edition, CBC Radio 1, 88.1 FM / 690 AM in Vancouver