Precast concrete box culverts save
large animals and costs to motorists

The Trans-Canada Highway through Banff National Park in Alberta, has a major effect on animals in the park. It is a barrier to natural wildlife movements. An average of 68 large animals are killed on highways in the park every year. Large animals on the road also pose a serious hazard to motorists. With over 14,000 motorists per day at the Banff park gates, it is clear that some measures must be taken to protect animals and motorists. Most of the Trans-Canada has been twinned through the park, with one-quarter of the most recent budgets for new twinning designated for measures to protect wildlife and the environment. These measures include fencing and wildlife crossing structures in the form of animal underpasses and overpasses.

Both wildlife and motorists will be protected by concrete underpasses.

Recently, Phase 3A of the twinning of the Trans-Canada through Banff National Park included four concrete box culvert wildlife crossing underpasses. The culverts are 3000 mm x 2400 mm in cross section. Three of the crossings are continuous under both sides of the highway, averaging 65 m long. One is a split crossing with a break at the median; each section is 32 m long. Precast concrete box culverts were especially suited to this application due to long service life, and ease of installation. Also included in this phase, were four metal culvert and two creek pathway underpass crossings, as well as two concrete arch overpass crossings.

Lafarge Pipe and Standard Products of Calgary designed and produced the box units for this project. They were designed to meet ASTM C789 and C850 since the range of cover was 0.3 m to 8.0 m. The boxes were designed for HS-32 highway loading, and had to meet the more stringent of CSA-S6 Bridge Code, or the Ontario Highway Bridge Design Code. A minimum concrete cover over reinforcement was specified to be 50 mm. The box units were produced in 2 m long sections with a dry-cast, vibration process to meet CAN3 A23.1-M90 and A23.4-M78 standards. An independent laboratory tested the concrete, and Public Works Canada representatives inspected the production, and the finished boxes. The box unit at each end of each crossing was produced with a 300 mm x 300 mm curb across the top to help grading and landscaping.

The boxes were installed by three contractors, Bremner Engineering and Construction (Canmore), Top Notch Construction (Calgary), and Selkirk Paving (Creston, BC). All three contractors elected to use a C-hook supplied by Lafarge to install the sections, rather than having the units made with lift holes that would have to be patched after installation.

The boxes were placed on a minimum 400 mm thick levelling pad of 20 mm crushed gravel. After installation, the top of the culvert and 0.5 m down each side were sealed with a membrane waterproofing which was covered during backfill with a 20 mm thick polystyrene protection board. Emulsified asphalt damp-proofing was applied on each side of the culvert below the membrane waterproofing. The length of the culverts was then lined with 75 mm-deep fine sand to create a more natural walking surface.

The Phase 3A wildlife crossing structures have been monitored since installation to determine their effect on wildlife movements. A monitoring progress report, including the first year of service, has just been completed. Wildlife visits were quantified by identifying tracks at 2 m wide raked sections at the entrances to the crossing structures every three days.

The report concentrated on large mammals (wolves, cougars, coyotes, bears, deer, and elk). All of these animals used the wildlife crossing structures during the year-long study, with 614 total visits to the 12 crossings, and 556 through-passages, for an overall through-passage percentage of 90.5%. All but the cougar (that only made one visit to any of the 10 structures) and the wolf (two visits) crossed using the concrete box culverts. Total visits to the four concrete box culverts numbered 174, with 160 through passages for an average through-passage of 92.0%. Monitoring is expected to continue until at least 2001 to determine how wildlife will respond and adapt to the structures.

It is encouraging to see effective measures being taken to protect wildlife and motorists through Banff National Park. Wildlife crossing structures have been used in other areas of the world with varying degrees of success. The results from the Banff studies and installations can add to the effectiveness of future designs.