This is a signal that an emergency vehicle is approaching and has activated a traffic control system, which systematically and safely changes the traffic signal to provide a “green” light for approaching emergency vehicles. The system is usually set so that the signal is received well in advance of the emergency vehicle’s arrival. It does systematically cycle through and doesn’t just change the opposing traffic’s signal without warning. This allows the intersection to clear and helps improve the responses to emergencies through intersections.

State laws — and common sense — dictate that vehicles yield to emergency vehicles that are operating their emergency lights and siren. Emergency vehicle drivers are taught to pass on the left whenever possible when responding in an emergency mode. When it’s safe, slow down, pull over to the right and stop. However, there are circumstances where that may not be possible (e.g., if you car is already stopped, and you don’t have anywhere to pull over). Simply stay put until the emergency vehicle goes around you. If you are blocking the route of the emergency vehicle, and you are able to pull ahead and over into a clear area, use your turn signal to indicate your intentions and proceed at a safe speed. Never slam on the brakes and stop in the middle of the road when you see apparatus approaching. Make no sudden moves. If an emergency vehicle is approaching from the opposite direction, you should pull over and stop. You have no idea if they are proceeding down the road, or are planning on turning into a driveway or intersection right in front of you. You are not required to slow down or pull over for emergency vehicles that are responding in the opposite direction on a divided freeway or highway. Do not tailgate, “draft,” or follow a responding apparatus closely. Not only is this illegal, you run the risk of collision as vehicles pull back out into traffic after the emergency vehicle goes by.

Sometimes several units are dispatched to the same incident. The first unit may have arrived on the scene, surveyed the situation and informed the dispatcher that the situation was under control. All other responding units were cancelled and put back into service, ready to take another call.

Most likely, when you see an emergency vehicle go “Code 3” (lights and siren) through an intersection and then slow down and turn the emergency lights off, they have been cancelled from the call they were going on.