33 Ligh t w eigh t , easy -t o -install , and v er y a ttr ac tiv e , T he T unable B ridge ™ tak es pr efabric a t ed st eel bridges t o a whole new dimension. t he t unable Bridge t M W ith clear spans of up t o 400, ' T he T unable B r idge TM is a str uc tur al h ybr id tha t’ s long on possibilities and shor t on c osts .