april 2005 ISSUE
BACKGROUNDER
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Deerfoot Extension Solves Technical, Environmental and Safety Problems
An extension to the Deerfoot Trail south of Hwy 22X in Calgary demonstrates some of the challenges and trends facing major highway construction projects in Alberta today, and points to possible solutions.
At the time, this project was the largest single project Alberta Transportation had given to any one engineering firm. The five-year, $100-million project involved an 11-kilometre extension to Deerfoot Trail, requiring three interchanges, a crossing of the Bow River and provision for wildlife to cross the roadway.
Opened to traffic Nov. 28, 2003, the work involved moving 12 million cubic metres of earthworks, 780,000 metric tonnes of granular material and 211,000 tonnes of asphalt.
UMA Engineering Ltd., through the firm's Calgary office, worked on the design and oversaw construction for the Bow River south section. UMA proposed that it lead a group of engineering firms for the entire project — the province's usual practice would have been to divide it into smaller projects and bids.
Being in charge of the entire project and using value engineering methods, UMA's team was free to come up with cost-saving ideas and make the work flow smoothly.
Congestion Relief Needed
This project was intended to solve a current and growing traffic congestion problem and improve the efficiency of the North-South Trade Corridor through the province.
The Deerfoot ( Alberta's Highway 2) is key to the transportation plans of both the city and province. Six-lanes for much of its length, the roadway ended at its southern end, then followed Highway 22X, a two-lane roadway, to Highway 2 South.
The result was traffic slow-downs that were particularly frustrating during morning and afternoon peaks. Commuters travelling to and from Okotoks, High River and other growing bedroom communities to the south mixed with highway truck traffic.
The Deerfoot Trail Extension has proven popular with users, with the new portion attracting about 60 per cent of traffic away from the old Highway 2 (MacLeod Trail). Deerfoot Trail traffic is now approximately 20,000 vehicles a day on the extension, growing to approximately 160,000 closer to the city centre.
Technical Challenges
Where the new Deerfoot Trail extension joins the old Highway 2, 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, using value engineering, and anticipating close to a 50 per cent 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 $4.8 million down to $2 million. It also improved safety during icy conditions, because the remaining structure is on a tangent instead of a tight curve.
Highway 2 northbound is marked with three overhead signs, starting two kilometres before the major fork, which 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 at the existing Highway 2/Highway 2A /Highway 551 interchange, where northbound Highway 2A traffic (from Okotoks) enters northbound Highway 2. Because of rapid growth in traffic out of Okotoks, the existing single-lane loop ramp was already over capacity, resulting in frequent traffic back-ups 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, P.Eng., from the University of Calgary, undertook research to determine the feasibility, safety, and appropriate design parameters for a two-lane loop ramp.
Two Loops Effective
Designers learned that two lane loop ramps operate very effectively in several locations in Canada and throughout North America. Several design features were incorporated to make the design as safe as possible. A painted “median” with rumble strips between the two lanes helps drivers stay in the correct lane; overhead signing in advance of the loop ramp indicates that the right lane over the structure must exit onto the right loop lane, while the left lane over the structure has the option to continue straight ahead or exit right onto the left loop lane.
Finally, both loop lanes join Highway 2 northbound as “lanes away,” giving traffic about 1.3 kilometres to merge left before only the right lane is dropped.
Environmental Issues
The original route of the highway would have interfered with a side channel in the Bow River. Although the channel is dry for part of the year, in the spring it forms a crucial low-current spawning area and habitat for juvenile fish.
Shifting the highway alignment 120 metres upriver avoided impact to this side channel. Although it added to the cost, it still resulted in net savings — interfering with the side channel would have required the creation of compensating fish habitat elsewhere.
The Bow River bridges were designed to span not only the river but also provide 30-metre-wide wildlife passage areas along both banks. To minimize river impacts, the original design had hammerhead piers and “drop-in” girders, resulting in longer spans and three sets of piers instead of four.
The bridge contractor (Penn-Co) and its sub-contractor (Con-Force) submitted an alternative design that replaced the hammerhead piers with conventional piers. They filled the resulting gap with 64 metre girders, the longest pre-cast concrete girders in North America at that time. This innovation significantly reduced the berming in the river that would have been required to construct the hammerhead piers.
Wildlife corridors were also constructed along both sides of the south highway embankment for about one kilometre, to the south escarpment. Wildlife fencing was placed along both sides of Deerfoot Trail for about three km 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 can also cross the highway through an 85-metre-long underpass about one kilometre south of the river, along the escarpment. This steel-plate underpass is four metres wide by seven metres high. A two-metre diameter skylight, in the centre 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.
Environmental impacts (and financial costs) were further minimized by using gravel obtained beside the construction site; this meant less material had to be hauled from a distance. The resulting pits were contoured and landscaped as ponds for wildlife habitat and planted with local species.
Eventually, this area may become part of Fish Creek Provincial Park. The “X” design of the bridge piers allows for possible future addition of pedestrian walkways under the bridge, to cross the Bow River.
Pond Protects Fish
South of the Bow, a two-hectare pond was built on the west side of the embankment that carries the roadway as it climbs out of the Bow River Valley, a rise of 50 metres from the bridge deck. This pond catches runoff from the bridge and roadway, settling out sediment before flowing into Pine Creek, which empties into the Bow River.
This protects fish against the hazards of sediment in their habitat — particularly important for trout survival.
The pond also permits easy and effective cleanup of hydrocarbon spills on the highway, as the overflow is taken from some depth below the surface of the pond. This would allow sufficient time to skim any hydrocarbons off the pond surface before they overflow to Pine Creek.
Where the Deerfoot Trail embankment covered Pine Creek, the creek was realigned for 170 metres of its length, with habitat restoration on a one-to-one basis and a three-metre culvert under Deerfoot Trail. The overall quality of fish habitat in the creek has improved from before construction. The design includes boulder fields, plunge pools, riffle zones and offset rocks to slow water flow rather than weirs. Replanting of vegetation used native trees and shrubs.
Using flat lenses on light standards minimizes light pollution escaping upwards, and drastically reduces glare. To provide adequate roadway lighting, the light standards are 18.3 metres high, compared with the usual 16 metres.
Finally, 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.
Safety Measures
Light standards were designed with break-away poles to reduce the severity of any collisions with them.
Also, all guard rail for the project is thrie-beam rather than the usual W-beam, to improve collision performance more frequently and consistently.
The highway's paved shoulders are 3.5 metres wide, forming a full lane for use of disabled or emergency vehicles. Beyond the paved shoulder, the roadway grade was built wide enough to allow for a six-lane cross section when future traffic demands it.
Summary
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. They say that it has taken some 20 minutes off their drive to work each day. It has also been of benefit to the motor transport industry as it eliminates stop and go traffic, and is a much more direct route.
The Deerfoot Trail Extension has been open to traffic for one year since Nov. 28, 2004. During its first year of operation, collision rates were very low on the Deerfoot Trail Extension, 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 that the project was built with all interchange structures in place on opening day, no traffic lights were required to stop through-traffic.
Partners
UMA's partners for earthworks and structures for the Bow River south section — as well as surfacing and other work for the entire project, including north to the Hwy 22X interchange — were AMEC Earth & Environmental, and Associated Engineering. Consultants for earthworks and bridges north of the river and the Hwy 22X interchange included Earth Tech Canada and EnviroConsult.
General contractors (and significant sub-contractors) included: Calibre Systems for earthworks from the Bow River to south of Dunbow Road, and the north portion of the Highway 22X interchange; Inland Construction for the south portion of the Highway 22X interchange and earthworks to 196th Avenue; Graham Construction for Highway 22X, 196th Avenue, Dunbow Road and fly-over structures, and (Northside Construction) earthworks south of Dunbow Road; Kidco Construction for earthworks south of 196th Avenue to the Bow River; Penn-Co Construction (Con-Force Structures) for Bow River Bridges; and South Rock for all surfacing south of Highway 22X and (Top Notch) remaining earthworks.
Editor's Note: Dwight Carter, P.Eng., was the project director, and Mike Bishop, P.Eng., was one of the consultant team leaders on the Deerfoot Trail extension. Reach them at dcarter@umagroup.com, mbishop@umagroup.com or 403-270-9200.
Author Credits
BY DWIGHT CARTER, P.ENG.
AND MIKE
BISHOP, P.ENG.
UMA Engineering Ltd.