This report presents the results from full-scale tests where the reversed airflow in different tunnels were measured. Two cases for each set up of fans were studied.In the first case the fans were placed standing free at the tunnel mouth downstream the natural airflow in the tunnel. The fans were started and the reversed airflow in the tunnel consisted of the primary flow through the fans plus the additional air due to entrainment. For the second case studied a tunnel cover was placed at the tunnel mouth with the fans placed in the middle. In this case the reversed airflow in the tunnel was given only from the primary flow through the fans. The results show that the tunnel cover can help to capture the counteracting wind force and create a potential pressure difference which makes it possible to reverse the flow in the full cross section and to ventilate longer tunnels than without the tunnel cover. The effects of the tunnel cover were also shown in model scale tests, where both the potential and the dynamic pressure were measured. The results from the tests will later be used to validate mathematical models.