The Holland 1\mnel, which has a fully transverse ventilation system, had to have lt. s cellb1g removed because of concrete deterloratlon. For more than a year before the Installation of a new ce! Ung, vehicular traffic would con· tlnue, and the ventilation system would operate In a semi· transverse mode. Evaluations were conducted to ascertain the capablllty of the ventilation system to maintain an acceptable environment during normal vehicular usage and in the event of fire. These evaluations included computations for varying traffic patterns and actual fire testing.

Once described as the eighth wonder of the world, the Holland Tunnel opened for use in 1927 and was designated a National Historic Civil and Mechanical Engineering Landmark on May 2, 1984. One of the reasons for conferring landmark status on the tunnel was an unprecedented ventilation system that made possible lhe longe t underwater vehicular tu1mel of the time. The tunnel consists of two independent tubes, each with two traffic lanes, approximately 8,500 ft long. Because of deterioration after nearly 60 years of operation, the ceiling, which forms a basic element of the ventilation system, had to be replaced. However, the tunnel tubes, which are a vital link in commuting and 1rucking routes in and out of New York City, could not be shut down for an extended period. All work-removals, measurements, and new constructionwould have to be done at night and the tunnel tube restored for traffic use each morning. The simplest way to implement such a staging requirement is to completely remove the existing ceiling, take measurements, and then prefabricate and install sections. This procedure would result in the twmel tubes being without a ceiling for more than a year. Evaluations and field tests were conducted to determine whether, without a ceiling, the ventilation system could