In situations of communication disasters or natural disasters, standard medical transport may not be sufficient. Thus, in many countries emergency and medical services (including those in the armed forces) have ambulances built on the basis of buses. Among them are constructions based on city buses, low-floor buses, adapted mainly for the transport of little injured people in sitting position and respective on stretchers. More advanced solutions are besides being developed, based on high-floor coaches, which are the mobile equivalent of infirmary emergency units (SOR).