When the Interborough Rapid Transit's first line opened in 1904, the subway proved to be more popular than envisioned. By 1908, a system designed for a maximum of 600,000 passengers per day was being used by 800,000. Arnold was called upon again to solve the problem. His solution was to place automatic speed control devices on the trains themselves, so that more trains could be run during each hour.[6]
On December 14, 1917, Arnold transferred to the regular Army as a lieutenant colonel in the Aviation Section of the Signal Corps. He was assigned to aircraft equipment production in Washington, DC. He was honorably discharged on Feb. 6, 1919. He was a colonel in the inactive reserve after 1929.[2]
^Tobin, Edward W. (2008). Before the North Shore Line: The Early Years 1894-1916. Chicago, Illinois: Central Electric Railfans Association. p. 37. ISBN978-0915348411.
^Clifton Hood, "The Impact of the IRT on New York City", Historical American Engineering Record survey number HAER NY-122, pp. 146–147, from www.nycsubway.org/articles/haer-impact-irt, retrieved September 3, 2007
^"Bion J. Arnold". IEEE Global History Network. IEEE. Retrieved August 8, 2011.
Greller, James Clifford (2014). The Men who Pioneered Electric Transportation. West Orange, NJ: Xplorer Press Inc. ISBN978-0-9853551-0-4. OCLC918986909.
Marquis Who's Who (1975). Who Was Who in American History - The Military. Chicago, IL: Marquis Who's Who. ISBN978-0-8379-3201-9. OCLC636066092.