Abstract: A convertible semi-trailer for highway and railroad modes of travel includes a coupler device to releasably couple adjacent vehicles end-to-end to form a train for the railroad mode. The coupler includes a male member extending from the end of one of the vehicles and the housing attached to the opposed end of the adjacent vehicles and having an opening therethrough for receiving the male member of the one vehicle. The male member is releasably locked in the housing opening for railroad mode of operation. A resilient pad is positioned in the opening of the housing and has the male member resting thereon to accommodate limited rolling, pitching and relative vertical displacement between the coupled vehicles.