Windshield fogging has been encountered in several bi-directional traffic road tunnels in Switzerland and other European countries. Tunnel safety is seriously affected in cases where this phenomenon occurs abruptly. Swiss authorities have therefore assigned a corresponding research program. This paper reports the first results of program's findings. Basically windshield fogging occurs in situations where temperatures inside the tunnel are higher than that of outside. Both the humidity of environment and the flow velocities within the tunnel are relevant parameters. In order to examine occurrence, systematic inquiries have been made with tunnel users. Additionally a tunnel has been equipped with dew point hygrometers and flow meters at each of the portals. Dew point control of the ventilation is scheduled as well as a modification of the tunnel ventilation in general. Condensation of tunnel air has to be considered in future ventilation design as the lower air exchange - due to the remarkable decrease of exhaust gas pollution over the last years, which leads to a more frequent appearance of condensation on vehicles. The research program will allow the taking into account of windshield fogging already during the design of the tunnel ventilation system and thus develop suitable ventilation control strategies.
展开▼
