The promoters or lessees, as the case may be, shall be answerable for all accident, damages, and injuries happening through their act or default, or through the Act or default of any person in their employment by reason or in consequence of any of their works or carriages, and shall save harmless all road and other authorities, companies, or bodies, collectively and individually, and their officers and servants, from all damages and costs in respect of such accidents, damages, and injuries.