Streetcar congestion in downtown Boston led to the establishment of subways and elevated rail, the former in 1897 and the latter in 1901. The Tremont Street subway was the first rapid transit tunnel in the United States. The grade-separated railways added transportation capacity while avoiding delays caused by intersections with cross streets. The first elevated railway and the first rapid transit line in Boston were built three years before the first underground line of the New York City Subway, but 34 years after the first London Underground lines, and long after the first elevated railway in New York City.