The Wireless Access for Vehicular Environment (WAVE) specifies that data packets of infotainment applications are to be sent within WAVE basic service sets (WBSS). These WBSS are to be established on the least congested service channels. WAVE proposes a mechanism to select such channels. Nevertheless, owing to high mobility in vehicular ad hoc networks (VANET), there is high chance of having overlapped WBSS, yielding unsatisfactory performance. Several approaches have been proposed to avoid such a scenario. Yet, they are either inefficient or cost-ineffective. In this paper, we propose ASSCH, an altruistic mechanism that impels vehicles to collaborate in order to select the least congested (i.e., used) service channel. ASSCH also includes a mechanism for WBSS termination, which is not specified in the WAVE standard. To the best of our knowledge, none of the existing works have proposed something similar. Simulation results demonstrate that our scheme handles the overlapping problem better and incurs high channel efficiency.