Previous research on response by grizzly bears to roads has been confined to interactions with tertiary or unimproved road systems. To our knowledge no information exists to evaluate the potential of high-speed, high-volume highways to disrupt or prevent grizzly bear movement. We know of no other area within occupied grizzly bear habitat in North America that has such an extensive network of high-speed, high-volume highways. Between 1994 and 1998 we captured and radio-marked grizzly bears in the Bow River Watershed, Alberta, and monitored their movements. Using radio telemetry data we documented the permeability of several highways to grizzly bear movement in a landscape where human presence is widespread. One highway with 24-hour, year-round high traffic volumes served as an effective barrier for adult female movement. Traffic volume appeared to be a key variable in the permeability of highways for grizzly bears. Highway crossings by grizzly bears were concentrated in specific locations and occurred during night as well as day. Our analysis demonstrates grizzly bears cross some highways in very site-specific locations, enabling us to predict crossing zones. Zones of high frequency road crossings in this study area were characterized by lower than average total access density, closer to a major drainage, more rugged terrain and higher quality habitat. Significant potential currently exists for permanent habitat and population fragmentation to occur along the Trans Canada Highway. An adaptive management approach will be crucial, with population connectivity being of paramount importance, as we continue to gain knowledge of grizzly bear response to highways.