With the consideration of the effect of non-motor vehicles on other lane without isolation belts, a modified coupled map car-following model is put forward. According to the feedback control theory, the stability conditions of the current vehicle influenced by non-motor vehicle on other lane are gained. The corresponding numerical simulations confirm the correctness of the theoretical analysis. It can be found that on the city roads without isolation belts, the headway between the preceeding and following vehicles on the current lane needs to be considered, and the influence of vehicles on other lanes (the transverse distance and the longitudinal distance) also needs to be emphasized. Finally, some suggestions for vehicle's travelling have been given.