Traffic volume and highway permeability for a mammalian community in the Canadian Rocky Mountains

We examined whether highway traffic volume changed the rates of movement (habitat permeability) for ten mammalian species in the central Canadian Rocky Mountains. Winter track count data were collected on four highways of varying traffic volume: the Trans-Canada Highway (TCH) (74,000 annual average daily traffic [AADT]) and 1A Highway (3,000 AADT) in Banff National Park and the Highway 40 (5,000 AADT) and Smith Dorrien Trail in Kananaskis Country (2,000 AADT). Permeability represented the ratio of road crossing tracks/km to tracks/km on transects adjacent to roads. We compared permeability at the community level and for carnivore and ungulate guilds, using a Kruskal-Wallis H-test. Traffic volume significantly reduced habitat permeability for the community (P 0.05). Pair-wise Kruskal-Wallis tests showed that habitat permeability was significantly reduced for carnivores at high traffic volume (P 0.008) and for ungulates at very high traffic volume (P 0.043). Cross-referencing with winter traffic counts, we found movement was impaired for carnivores when traffic ranged from 300 to 500 vehicles per day (VPD) and for ungulates between 500 and 5,000 VPD. Our results indicated that the TCH requires mitigation to restore habitat permeability for all species and yielded strong evidence that the Highway 40 is a priority for mitigation.