The entrance tollgate of expressway is in severe vibration environment caused by the traffic. In order to detect the deterioration of the roof slab of reinforced concrete tollgate supported by a single row of columns, traffic-induced vibration of the roof slab was measured for about two years. The results obtained from the long-term monitoring show that the Lissajous figure of displacement, angle of the slab, the first natural frequency and stiffness in the vertical direction are important and valid for detecting the deterioration of the roof slab as monitoring methods.
