sentences:  Like the situation with roads, the Darien Gap is a formidable obstacle to railroads, and no railways cross it into South America.The continent's roads are of varying quality, with divided highway standards in some areas but poor-quality gravel or unpaved roads in others.The road network extends from Prudhoe Bay, Alaska, and Anchorage, Alaska, in the extreme northwest, to Sydney, Nova Scotia, Cartwright, Newfoundland and Labrador, Blanc Sablon and Natashquan, Quebec, in the extreme east, all the way to Yaviza, Panama, in the extreme south.