of The Big Walker Mountain Tunnel in Virginia. With his firm Singstad and Baillie in New York, he designed the Baltimore Harbor Tunnel, which opened in 1957. Singstad also designed tunnels in Argentina, Canada, Cuba, and Venezuela. Pioneering techniques Ventilating the Holland Tunnel Thomas Edison had contended it was impossible to ventilate a tunnel with the volume of traffic envisioned for the Holland Tunnel. At the time of its construction, underwater tunnels were a well-established part of civil engineering, but no long vehicular tunnels had been built, as all of the existing tunnels under New York City waterways carried only railroads and subways. These tubes did not have as much of a need for ventilation, since the trains that used the tubes were required to be electrically powered, and thus emitted very little pollution. On the other hand, the traffic in the Holland Tunnel consisted mostly of gasoline-driven vehicles, and ventilation was required to evacuate the carbon monoxide emissions, which would otherwise asphyxiate the drivers. There were very few tunnels at that time that were not used by rail traffic; the most notable of these non-rail tunnels, the Blackwall Tunnel and Rotherhithe Tunnel in London, did not need mechanical ventilation. However, a tunnel of the Hudson River Tunnel's length required an efficient method of ventilation, so Chief Engineer Singstad pioneered a system of ventilating the tunnel transversely (perpendicular to the tubes). In October 1920, General George R. Dyer, the chairman of the New York Tunnel Commission, published a report in which he stated that Singstad had devised a feasible ventilation system for the Hudson River Tunnel. Working with Yale University, the University of Illinois, and the United States Bureau of Mines, Singstad built a test tunnel in the bureau's experimental mine at Bruceton, Pennsylvania, measuring over long, where cars were lined up with engines running. Volunteer students were supervised as they breathed the exhaust in order to confirm air flows and tolerable carbon monoxide levels by simulating different traffic conditions, including backups. The University of Illinois, which had hired the only professors of ventilation in the United States, built an experimental ventilation duct at its Urbana campus to test air flows. In October 1921, Singstad concluded that a conventional, longitudinal ventilation system would have to be pressurized to an air flow rate of along the tunnel. On the other hand, the tunnel could be adequately ventilated transversely if the compartment