The Alliance for Water Efficiency (AWE) and ...
Canadian freeway extension solves technical, environmental and safety issues
High world oil prices have fueled the growth of Calgary, capital of the Canadian oil and gas sector. New residents have pushed the city’s population to more than 900,000, and prosperity has given it the highest per-capita vehicle ownership in North America.
The result: slowdowns on the city’s network of “trails,” the name given to its multilane expressways, particularly the Deerfoot Trail. Six lanes for most of its length through the city, the Deerfoot is an important link in the North-South Trade Corridor through the province and into the U.S.
Growing transport traffic added to the effect of morning and afternoon drive times as commuters from the bedroom communities south of Calgary swelled traffic volumes. Much of the resulting slowdown occurred at the southern end of the Deerfoot, also known as Provincial Highway 2, where the roadway continued onto the two-lane Highway 22X, and then continued to Highway 2 South.
The province of Alberta wanted a solution. It would need to be cost-effective, because while provincial royalties from oil and gas have been impressive, so have demands on the provincial coffers to pay for infrastructure to support the increased population. The solution also would have to factor in rising environmental concerns and demand for safety—and meet the pressing need for results sooner rather than later.
The plan: extend the southern end of the Deerfoot by seven miles, including three interchanges. One of the key challenges was meeting rising environmental obligations in crossing the Bow River, which rises from a glacier in the Rocky Mountains and is one of the premier trout-fishing rivers in North America.
UMA Engineering Ltd., based in Vancouver, British Columbia, and a member of the AECOM Group of Cos., proposed that it lead a group of engineering firms for the entire project, rather than having it divided up among different consultants as is the province’s usual practice. This idea was accepted by the client, Alberta Transportation. Being in charge of the entire project allowed the team to come up with cost-saving ideas, and the work flowed more smoothly. The major sub-consultants on UMA’s team included Amec Infrastucture Ltd., Associated Engineering Ltd. and Amec Earth & Environmental Ltd.
The five-year, $81 million project involved moving 16 million cu yd of earthworks, 860,000 tons of granular material and 234,000 tons of asphalt.
Opened to traffic in November 2003, the extended Deerfoot has proven popular with users. The new portion has attracted about 60% of traffic away from the old Highway 2 (also known as Macleod Trail). Deerfoot Trail traffic is now about 20,000 vehicles per day on the extension, growing to approximately 160,000 closer to the city center.
Use your fork
Where the new Deerfoot Trail extension joins the MacLeod Trail, the approaching roadways form a “Y” configuration. UMA’s team wanted a cost-effective and safe way for northbound drivers on the Deerfoot to exit onto the parallel Macleod Trail.
Previous functional plans used a conventional right exit followed by a curving left ramp over northbound and southbound Deerfoot Trail to MacLeod Trail. However, anticipating close to a 50-50 split between MacLeod Trail and Deerfoot Trail traffic, the designers developed a “major fork,” with Macleod Trail splitting left and Deerfoot Trail splitting right.
This shortened, grade-separated structure now only goes over southbound Deerfoot Trail, taking the original design’s price tag of $3.8 million down to $1.6 million. It also improved safety during icy conditions, because the remaining structure is on a tangent, instead of a tight curve.
MacLeod Trail northbound is marked with three overhead signs, starting about a mile before the major fork, that allow drivers to visualize this unconventional (for Alberta) type of junction and get into the correct lane.
Another innovative design feature is a new dual-lane loop ramp where a major feeder road, Highway 2A, enters northbound MacLeod Trail.
Because of rapid growth in traffic out of the southern bedroom communities, the existing single-lane loop ramp was already over capacity, resulting in frequent traffic backups onto the structure. Previous functional plans had an interim dual left turn and traffic signal (diamond interchange configuration) and ultimate directional fly-over ramp.
UMA’s team, with the assistance of Dr. John Morrall from the University of Calgary, undertook research to determine the feasibility and best design for a two-lane loop ramp instead.
Through this research, designers learned that two-lane loop ramps operate very effectively in several locations in North America. They were therefore used in the final design, adding safety features such as a painted median with rumble strips between the two lanes to help drivers stay in the correct lane and overhead signage well in advance. Both loop lanes join MacLeod Trail northbound as “lanes away,” giving traffic about 1,400 yd to merge left before only the right lane is dropped.
Where the wildlife roam
Rising environmental concerns were particularly noticeable in the crossing of the Bow River.
One issue was a seemingly minor side channel which is dry much of the year. However, in the spring it forms a crucial low-current spawning area and habitat for juvenile fish. Interfering with the channel would have required creating compensating fish habitat elsewhere, at significant cost. There was a net savings in shifting the highway alignment 120 yd upriver to avoid impact on the side channel.
Allowing wildlife safe passage across the roadway is very important, so the bridges were designed to not just cross the river, but provide 30-yd-wide wildlife passages under the bridge along both river banks. To allow this, the bridge uses 210-ft girders, which were the longest precast concrete girders in North America at the time, allowing conventional rather than hammerhead piers. This significantly reduces the amount of berming needed in the river.
Wildlife is further protected by 1,000-yd-long corridors along both sides of the south highway embankment as it climbs the south escarpment. Wildlife fencing was placed along both sides of Deerfoot Trail for about two miles south of the Bow River, keeping animals off the highway and directing them to the corridors. To encourage wildlife use, the team calculated the area of trees that would be disturbed by construction and then planted equivalent areas in the corridors.
Wildlife also can cross the highway through an underpass about 1,000 yd south of the river along the escarpment. This 90-yd-long steel-plate underpass is about 23 ft wide by 12 ft high. A 6-ft-diam. skylight in the center of the highway median allows natural light to enter the tunnel. Deer and other animals were crossing the roadway through the underpass even before construction was finished, and this has continued.
To reduce environmental impacts and financial costs from transporting aggregate material, gravel was used from beside the construction site. The resulting pits were contoured and landscaped as ponds for wildlife habitat, planted with local species.
The bridge was designed with future recreational use in mind. The area may become part of a municipal park, so the “X” design of the piers allows for adding a pedestrian walkway across the river under the bridge.
To avoid fish-threatening sedimentation of the river water, a 5-acre settlement pond was designed to catch runoff from the bridge deck and roadway as it climbs out of the valley south of the river.
Because the pond’s overflow is taken from some depth below the water’s surface, oil and other spills on the road are easier to clean up. Pollutants can be skimmed off the water before they reach the river.
Another environmental measure is found in the street lights on the roadway, which use flat lenses to minimize light pollution escaping upward. They also minimize glare. To provide enough lighting on the roadway, the light standards are 60 ft high, compared with the usual 52.5 ft.
Throughout the project, extensive use was made of erosion-control matting, environmental ditch dams and other measures to promote quick growth of ground cover and minimize erosion.
Contractors also were required to develop erosion control and operations plans. The first such plans on the Deerfoot Trail extension became the model for “ECO plans” now required on all Alberta Transportation projects.
A time saver
In addition to completing the “missing link” in the north-south trade corridor through Alberta, the Deerfoot Trail Extension has made life easier for many Calgary commuters, who say that it has taken some 20 minutes off their drive to work each day. It also has been of benefit to the motor transport industry because it eliminates stop-and-go traffic and is a much more direct route.
In the year since it opened, collision rates have been very low, and driver reports have been very positive and complimentary. Drivers have adapted very well to the two-lane loop ramp and major fork, and environmental agencies are very satisfied that this project has met its goal to “mitigate impacts through good design and construction practices.”
Drivers are particularly appreciative of the fact that the project was built with all interchange structures in place on opening day, so that no traffic lights were required to stop through-traffic.