A Montana judge has halted the transportation of massive oilfield equipment across the state’s roads. Imperial Oil, a subsidiary of Exxon Mobil, has been barred from using Montana’s scenic highways to transport hundreds of tons of equipment to Alberta, Canada, for a controversial tar sands pipeline project. The National Wildlife Federation, Missoula County and a number of conservation groups had argued oil companies and the U.S. Department of Transportation had failed to attain the necessary environmental clearances.