The Ljubljana–Razdrto highway and the parallel Ljubljana–Trieste railway cut through critical brown bear (Ursus arctos) habitat in south-central Slovenia. These high speed, high volume traffic axes are located close to the main dispersal corridor for bears from the Dinaric Mountain range into the Alps. We analyzed radiotracking data of 15 individual bears that lived within 10 km of the highway, compared transportation related and overall known bear mortality, and analyzed the spatial distribution of bear–vehicle accidents. The highway posed a home range boundary to resident bears, but was not an absolute barrier. Transportation-related mortality was high in the vicinity of the highway and railway, and averaged 31% of the total known local mortality from 1992 to 1999. At present the detrimental impact of transportation routes on the bear population in Slovenia is modest due to the high density of bears and the low density of highways—but new highways are planned or already under construction. Managers have to be aware that, due to bears large home ranges and long dispersal distances, a single highway affects bears from a huge area—emphasizing the importance of international cooperation and a landscape approach in highway planning.