The Manitou and Pike's Peak Railway, with a summit elevation of 14,110 feet above sea level, is the highest railway in North America and the world's highest cog railway. It was the third and last cog railroad built in the United States after a construction period of 13 months, and the first passenger train ascended Pike's Peak on June 30, 1891. The idea for building a cog railway up Pike's Peak is accredited to Major John Hulbert of Manitou, and funding for the line was provided by Zalmond Simmons, head of the Simmons Mattress company. The railway has operated continuously along the same route since 1891. Steam engines were the only motive power on the line until 1938, and by 1958 the last steam locomotives had been retired from passenger service and replaced by the first generation of diesel-electric trains. Cog, or rack, railways are designed to allow trains to climb much steeper angles than standard railroads, and to climb the line's maximum 25 percent grades the railway employs the Abt rack system, a rack-and-pinion gear drive for trains invented by Dr. Roman Abt of Switzerland in 1882.