Emergency ambulances are highly likely to be involved in hazardous situations, including incidents such as a road traffic collision, as these emergencies create people who are likely to be in need of treatment. They are required to gain access to patients as quickly as possible, and in many countries, are given dispensation from obeying certain traffic laws. For instance, they may be able to treat a red traffic light or stop sign as a yield sign ('give way'), or be permitted to break the speed limit. Generally, the priority of the response to the call will be assigned by the dispatcher, but the priority of the return will be decided by the ambulance crew based on the severity of the patient. Patients in significant danger to life and limb (as determined by triage require urgent treatment by advanced medical personnel, and because of this need, emergency ambulances are often fitted with passive and active visual and/or audible warnings to alert road users.