Thursday, February 27, 2014

The Mystique of the Deh Cho Bridge


The Mystique of the Deh Cho Bridge

By Kotone Noda
The Daily Magi
September 9, 2064

The Deh Cho Bridge is a 1.1 km (0.68 mi) long bridge across a 1.6 km (0.99 mi) span of the Mackenzie River on Highway 3 near Fort Providence, Northwest Territories, Canada. Construction began in 2008 and was expected to be completed in 2010 but faced delays due to technical and financial difficulties. The bridge officially opened to traffic on November 30, 2012. The bridge replaced the prior ferry/ice bridge combination used for river crossing, replacing MV Merv Hardie, the ferry in operation at the time of opening. Deh Cho is the Dene name for the Mackenzie River.

NWT Highway 3 (or the Yellowknife Highway) must cross over a kilometre of open water on the Mackenzie River south of Fort Providence. Since the highway opened in 1960 through November 2012, a seasonal ferry service was provided (roughly mid-May until December or January), with an ice road maintained across the frozen river from December to April. During the spring "breakup" season, due to hazards from floating or jammed ice there was a 3-4 week period (from mid-April to mid-May) between the closing of the ice road and the start of ferry service. No vehicles could cross during this period, and supplies for Yellowknife and other highway communities north of the river had to be relayed across by helicopter, sent by air freight, or wait until ferry operations begin. A similar but shorter "freezeup" period used to occur in December/January between the end of ferry operations and the opening of the ice road, but since the early 1980s ferry operations had generally been able to extend until the ice road was open.

The closing of the crossing created added transportation inconveniences and costs for residents north of the river, especially for perishable items such as food. A bridge had been of interest since the highway was opened, but various proposals for a bridge had difficulty establishing financial feasibility given the limited traffic volumes and the estimated construction and maintenance costs involved.

The original design was completed by JR Spronken and Associates Ltd. of Calgary in 2002. Following the GNWT's independent review, performed by its consultants BPTEC of Edmonton and T. Y. Lin International of San Francisco, recommendations for changes to the superstructure design were made. Infinity Engineering Group of Vancouver carried out the redesign and is now the design engineer firm on the project.

Infinity Engineering Group's project description says:

The superstructure is a two lane, nine-span composite steel truss bridge with a cable assisted main span of 190 m. The approach spans are symmetrical about the centre of the bridge and have successive lengths of 90 m, 112.5 m, 112.5 m and 112.5 m. The total length of the bridge is 1,045 m. The superstructure consists of two 4.5 m deep Warren trusses with a transverse spacing of 7.32 m and a 235 mm thick precast composite deck. The truss members are built up I-sections. Two A-pylons, located at Pier IV South and Pier IV North, each support two cable planes. Each cable plane consists of six cables that are connected to the main truss through an outrigger system.

The bridge makes significant use of "weathering" steel and will not be painted, reducing maintenance costs and extending the projected lifetime. It has fairly minimal lighting, citing dark-adaptation for drivers and reduced risk to migratory birds.

The original construction budget was $169 million. This was mainly financed by the issuance in 2008 of $165.4 million in inflation-linked real return bonds, paying 3.17% plus inflation adjustment. The bonds will be repaid over a 35-year period from December 2011 (interest only was paid from 2008). This will amount to approximately $275 million in principal and interest costs over the 35 years, before the inflation adjustments.

With the construction difficulties that caused the GNWT to assume control of the project in 2010, another $15.9 million in financing was required, which was provided by the government in its 2012/2013 capital estimates and brought the construction budget to $182 million. A further $10 million announced as being required in June 2012, brought the construction budget to $202 million.

Some items are not included in this figure, including costs for building toll plazas and other toll infrastructure (estimated at roughly $1 million), compensation for lost fish habitat, and environmental remediation. The cost of various remediation repairs to the original Atcon Phase 1 work is not included; this is being paid for by the $13.3 million construction bond funded by the New Brunswick government. Also not included are the indirect costs of the most recent delay to 2012 in opening the bridge; a year's worth of uncollected tolls and additional ferry operation.

The bridge now having been built, annual expenditures by the GNWT will approach $9 million, including principal and interest repayment, toll collection costs, bridge maintenance and the Opportunities grant to Fort Providence community groups. Along with the tolls, the government will save an estimated $3 million annual savings in ferry costs, but is anticipating a further subsidy requirement of around $2 million annually, depending on traffic volumes.

The bridge was awarded the 2013 Gustav Lindenthal Medal for "demonstrating harmony with the environment, aesthetic merit and successful community participation" by the International Bridge Conference. Steven Sternberger, presenting the award, said "The Deh Cho Bridge stands as a commendable example of using innovative design to meet stringent challenges, such as site conditions and location, schedule and budget constraints, while also creating an iconic, landmark structure".

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