It shall be unlawful for any person to tie to any motor vehicle which is operated on the streets of the city any sled, toboggan or similar contrivance or thing; and it shall be unlawful for the operator of any motor vehicle to permit any sled, toboggan or similar contrivance or thing to be attached or tied to any motor vehicle being driven by the operator; provided, that the provisions of this section shall not apply to trailers, bus trailers or pole or pipe dolly, nor to cars being towed, when the same are attached or towed in accordance with this chapter.