Traffic congestion has a fundamental impact on ventilation operation in case of unidirectional traffic, particularly if a longitudinal ventilation system is used. Existing technologies for congestion detection are generally based on CCTV, inductive loops in the pavement or other kinds of counting devices. New radar-based technologies recently became available on the market. In the framework of ventilation design for Zürich’s Northern Bypass, a specific experimental campaign for comparing and assessing three potentially viable technologies (traffic counting sensors, CCTV and newest-generation radar sensors) was carried out in the 3.3 km long Gubrist tunnel. Based on the results, the relative advantages and drawbacks of the different technologies could be assessed under real-life conditions. Both CCTV and radar sensors proved to be viable technologies for this specific application. Based on the results, it was decided to implement a radar-based solution in the short Katzensee tunnel (0.58 m) and a CCTV-based solution in the three tubes of the Gubrist tunnel (3.3 km).

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