The original bus icon from the derived file (openclipart.org/detail/18110/vehicles-silhouette) has wheels that are not perfect circles. I isolated the bus icon, removed the wheels and replaced them using the Inkscape "draw circle" tool.
公共汽車標誌/象形圖
bus、Cars、icon、pictogram、Spring One 2017、symbol、vehicle
總線、汽車、圖標、圖標、2017年春季、符號、車輛
資料來源：openclipart ( https://openclipart.org/ )