Emergency Medical Service shorthand for "Red light and siren", or the operation of an authorized emergency vehicle in response to an emergency call. RLS operation permits the driver to operate the vehicle under a different set of traffic rules than apply in "cold" or non-responding situations.
New Jersey law (N.J.S.A. 39:4-91) states that "The driver of vehicle upon a highway shall yield the right of way to any authorized emergency vehicle when it is operated...in response to an emergency call...and when an audible warning bell, siren, exhaust whistle or other means is sounded...and when the authorized emergency vehicle is equipped with at least one lighted lamp displaying a red light visible under normal atmospheric conditions from a distance of at least 500 feet to the front of the vehicle."
Based on the data provided to the vehicle operator by the dispatcher, an emergency can be said to exist from the time of dispatch until the time of arrival at the scene.
Upon departure from the scene, determination of an emergency situation depends on the diagnosis and condition of the patient at the time of pick-up from the scene, based on the discretion of the senior EMT. A non-emergency can also change into an emergency en route based on the progression of the patient's condition.
New Jersey law (N.J.S.A. 39:4-91) further states it "... shall not relieve the driver of any authorized emergency vehicle from the duty to drive with due regard for the safety of all persons, not shall it protect the driver from the consequences of his reckless disregard for the safety of others."
RLS is a privelege granted to operating EMT workers for the safety and well-being of the patient, but comes with enormous responsibility and inherent risks.