The frequency of caribou, Rangifer tarandus, crossing of roads, pipeline, and pipelines along roads was studied in the Prudhoe Bay and Kuparuk oil fields on the Arctic Coastal Plain of Alaska. Caribou crossed an elevated pipeline or a road with a frequency similar to the control. It was only where a pipeline paralleled a road with traffic, that crossing frequencies were significantly less than expected (30% versus 66%). It is postulated that vehicles act in a synergistic fashion with a pipeline to produce a negative stimulus that results in decreased crossing frequency. Caribou crossing under elevated pipelines did not select for particular pipe heights within the range studied (152-432 cm). Caribou did select buried sections of pipeline as crossing sites more often than expected.