High-Altitude Multiple-Vehicle Emission Tests

Colorado is undertaking construction of urgently needed dual vehicular tunnels through the Continental Divide at an elevation of approximately 11,000 ft. There are no existing heavy volume tunnels at this elevation. Special problems in connection with the 8,800-ft-long tunnels include the fact that human tolerance to carbon monoxide (CO) is significantly decreased as the altitude increases, and CO emissions from vehicles increase with altitude. It was necessary to develop new design criteria beginning with multiple emission tests at various grades, speeds, and altitudes. In addition, CO emissions on a single engine under rigorously controlled laboratory conditions were conducted. The results of these tests, together with previously determined data at lower elevations by the Public Health Service were used to arrive at design criteria of the tunnels.