What is OptiCom?
The OptiCom system, designed by 3M, is a traffic control system that provides a green light - and therefore intersection right-of-way - to emergency vehicles.  Equipped vehicles have an emitter, which broadcasts a visible light or invisible infrared signal to a receiver, which is mounted on or near the traffic signal.  When the receiver detects a recognized signal, the notifier (a floodlight mounted on or near the traffic signal) is activated as the traffic signals change to allow priority access as requested.  Minneapolis/St Paul Metro area signals equipped with OptiCom utilize the notifier, however many OptiCom installations nationwide do not utilize the notifier element and have no visual signal of an activation.

Below are the two scenarios that drivers may encounter with OptiCom activations in the Minneapolis/St Paul Metro area.  These scenarios will tell you in detail how to react to these activations.  However, if this information is too much to remember, simply continue to obey normal traffic laws in regard to traffic signals during an activation, using extra caution in the knowledge that emergency vehicles are responding nearby.

The floodlight on my traffic signal is flashing, what does it mean?
An emergency vehicle is approaching the intersection from a different direction, either towards you or from the side.  If your traffic signal is green, it will change to yellow and then red in a few seconds*.  DO NOT try to beat the red.  If you have not yet entered the intersection, and if conditions safely allow, pull safely and carefully to the right side of the road and wait until the light stops flashing.  If you passed through the intersection, be aware that one or more emergency vehicles could soon turn onto the road behind you, so be prepared to pull over if necessary.  (* Exception:  Some intersections with simpler traffic signal controllers do not have the ability to go green in one direction only.  For example, your choices might be green for East-West or green for North-South.  In these cases, you could see the notifier flashing and still get a green light.  If this occurs, the emergency vehicle is approaching the intersection from the opposite direction.  Unless you are in danger of being rear-ended, treat it as a red light.)

The floodlight on my traffic signal is on and not flashing, what does it mean?
An emergency vehicle is approaching the intersection in the same direction that you are.  It is either in front of you or behind you, and there may be more than one.  If the traffic signal is red, it will change to green shortly.  If you have not yet entered the intersection, and if conditions safely allow, pull safely and carefully to the right side of the road and wait until the floodlight turns off.  If you are in a large group of traffic that had been waiting at a red light before it turned green with the floodlight, pull as far forward up to or through the intersection as necessary to be able to safely and carefully pull to the right side of the road to make room for emergency vehicles to pass.  Do not block the intersection.  Remain pulled over until the floodlight turns off, or if you passed through the intersection, until you cannot see or hear any emergency vehicles.

All about OptiCom, in layman's terms

Almost all of the traffic signals in the Twin Cities Metro area have been converted to employ the use of 3M's OptiCom traffic pre-emption device.  Intersections so equipped are usually easy to identify by the presence of a receiver, and most equipped intersections also have a notifier, a visual signal device, which is simply a clear floodlight for each directional approach to the intersection.

When an equipped intersection detects a confirmed pre-emption signal from an emergency vehicle equipped with an emitter, all of the floodlights begin to operate immediately.  The floodlight aimed in the direction from which the activation was received will illuminate and remain on in a steady burn, to notify the operator of the emergency vehicle that the traffic signal has acquired the request to pre-empt traffic.  The remaining floodlights, aimed in all other directions, will begin flashing, which serves two purposes.  First, all other traffic will have a specific signal informing them that this is not just any ordinary red light, but that an emergency vehicle is approaching the intersection.  This will hopefully encourage drivers to not take any free right turns or try to run a late yellow light, and just sit tight until the emergency vehicle passes.  Second, and more importantly, in the event more than one emergency vehicle is approaching the intersection at the same time from different directions, the flashing signal communicates to the emergency vehicle driver who was not granted pre-emption that another emergency vehicle has acquired the green light in a different direction.  This driver must now take extreme care in approaching and proceeding through the intersection, since they will probably not have a green light when they get there.  One of the greatest dangers to responding emergency vehicles is not being able to hear each other's sirens when more than one of them approaches the same intersection at the same time.  It is not uncommon, however, for an intersection to quickly grant access to additional emergency vehicles approaching from different directions after the first has already passed.  In any case, if you are at a red light and see the floodlight in front of you flashing, you can check the other floodlights to find the one not flashing (staying on), and therefore figure out from which direction the acquired emergency vehicle is approaching.

Emergency vehicle operators should consider that the OptiCom pre-emption is not instantaneous.  When a traffic signal receives an activation, it has pre-programmed normal tolerances that it must cycle through to ensure all traffic is clear of the intersection before providing a green light to the approaching emergency vehicle.  This may simply require the normal lag time for other directional signals to turn yellow and then red, including the normal all-red delay.  In some cases this lag time may be extended when a pedestrian signal must also be cleared, since pedestrians must be given extra time to clear an intersection before a green light is granted which could expose them to traffic.

OptiCom systems in emergency vehicles are generally electronically integrated with the vehicle's transmission or shifting linkage, which basically means that the system is automatically deactivated when the vehicle is shifted into "Park".  In this way, a traffic signal is not locked down and held in green indefinitely when an emergency vehicle is parked facing an intersection while on the scene of an emergency.

Generally, OptiCom systems can be installed to simply recognize any confirmed pre-emption signal, or they can be further customized and linked to computer-aided dispatch systems that are capable of identifying which emergency vehicle pre-empted the signal, as well as the time and direction of travel when the signal was pre-empted.  Using this identifying capability, OptiCom can even be used to determine pre-emption priority when two signals are received at the same time.  For example, some regions (Seattle, for example) also use OptiCom with public transportation, to ensure buses remain on time, and the priority capability would allow a police car or fire truck to "trump" a bus for the green light.  Twin Cities Metro OptiCom installations are not currently configured to allow mass transit to utilize the system.  Other variations have been noted, as in Bismarck ND, where the notifier is directed through a green lens.  Many other locations (Tacoma WA, Portland OR, Billings MT to name a few) do not have any notifier installations at all, so activated traffic lights give no other visual indication of pre-emption other than the fact that they turned green for the approaching emergency vehicle.

Contrary to urban legend, 3M's OptiCom system cannot be spoofed by flashing your high beams, as it is activated by a visible light or invisible infrared signal, operating at a specific "flash-rate" frequency.  No OptiCom receiver will be fooled by someone flashing their high beams, since typical activation settings for an OptiCom system are around 600 or 900 FPM (flashes per minute), or 10 to 15 "flashes" per second.  Imagine trying to transmit a fax by whistling into the telephone, and you can imagine the challenge of activating an OptiCom system with your high beams, it is just not possible.  Some will claim it works for them, but almost every intersection has a detection system to identify when a vehicle is waiting for a red light, so it is no surprise that the light eventually turns green while they sit there wearing out their high beam switch.

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