Fogging of windshields in road tunnels - synthesis (ASTRA2001/013)
Overview
Background & policy context:
When a car enters a tunnel, the occurrence of water condensation on the outside of the front shield is possible if air temperature and/or humidity in the tunnel are higher than outside. Due to cooling of the tunnel air on the surface of the vehicle, the temperature can fall below the dew point and therefore condensation on the surface occurs. Because of sudden appearance and reduction of the driver's view, this phenomenon presents a remarkable potential for danger.
Objectives:
The main objective of the project was to develop tools for predictions and by means of surveys with tunnel users, theoretical studies, model calculation and measurements in three affected tunnels to propose measures reducing the appearance of windshield fogging.
Beside the suggested measures, the final report shall contain recommendations which have been made to be included in the Swiss guideline "Ventilation of Road Tunnels".
Methodology:
The project was worked out in three steps:
1. Through a survey of the Cantonal (Provincial) Authorities, it was investigated in which tunnels windshield fogging occurs in Switzerland. The phenomenon is reported to occur in a total of 19 Swiss road tunnels.
2. In selected tunnels indoor-air climate measurements were carried out
3. Measures were suggested to reduce the appearance of windshield fogging.
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