MIRT (Mobile Infrared Transmitter) FAQ
What is the Operational Range?
The Distance Between the Vehicle and Traffic Signal (applicable to any system, any manufacturer)
What determines range?
MIRT, 3M Opticom®, and Tomar Strobecom® traffic signal preemption are optically-based communications systems. There are three major factors that determine range in any optical system: the transmitter (power supply and strobe head located in the vehicle), the detector (also known as the “receiver” normally located on or near the traffic signal), and the optical medium between them (air).
In a perfect world, the transmitter is working perfectly and the lens covering the strobe head is perfectly clean; the detectors sensitivity is optimally set, the detector’s lens is perfectly clean, and the traffic signal electronics are functioning correctly; and there is no visible obstruction between the transmitter and detector, no fog or bad weather. It is reasonable to expect any working “system” to function properly at a distance of between 150 feet and 1800 feet, the distance between vehicle-mounted transmitter and the traffic signal detector.
The most common circumstances reducing range are as follows:
Transmitter: Dirty lens, electronic failure of the power supply, faulty strobe head, insufficient power supply input voltage, and faulty cables and/or wiring harnesses can decrease or prevent a system from working properly. Removal of the Infrared Filter on the MIRT will provide much better range.
Detector: Decreased range or system failure can be caused by a dirty lens, electronic failure of the preemption detector or traffic signal electronics (damage due to lightning, circuit component failure, etc.), power outage to the intersections, improper sensitivity settings, improper aiming of the “telescopes”, improper mounting locations, or detectors which have been pre-programmed to only permit vehicles that can transmit encrypted ID optical signals (Note: See “Will the MIRT work with encoded detectors?” for specific information related to encrypted ID optical signals)
Medium: The line-of-sight between the transmitter and detector can be compromised by fog, smog, snow, rain, sleet, hail, dust, wind (detectors mounted on suspended lines can sway and/or rock in the wind, interrupting the line-of-sight), or any combination of the aforementioned. The line-of-sight can also be obstructed by other vehicles (notably large trucks), large traffic signs, overpasses (normally due to improper location of the detector, which can often be corrected by either relocating the detector or adding another detector), or any non-transparent physical obstruction.
How can optimum system range be achieved?
Removal of the Infrared Filter and proper location of the MIRT when installed inside the vehicle windshield. The Mirt should be installed with the suction cups high on the windshield to provide a better line of sight. The MIRT should be mounted to point straight forward and be level.
System range optimization is a balance between the user’s needs and the preemption equipment’s capabilities. For instance, if the equipment used claims a line-of-sight operation up to 1800 feet, yet your requirement is 2500 feet, then no optimization on the part of the user will overcome the product’s limitations.
Physical obstructions that cannot be resolved by relocating the detector (receiver) or adding another detector can also not be improved upon. It is assumed that the reader has established that the system is, in fact, working, although the range has been determined to be substantially less than stated in the product specifications bulletins.
Assuming an unobstructed line-of-sight between the transmitter and detector of 1800 feet, clean transmitter and detectors lenses, and that both electronic systems are fully operational, suggestions for improving the range of any intersection are as follows:
- Make certain that the detector is mounted and aimed properly (refer to the manufacturer’s product manuals).
- Make certain that the MIRT is properly mounted on the vehicle and is not optically occluded (obstructed or partially blocked), and relocate if necessary.
- Increase the sensitivity of the detector (refer to the manufacturer’s product manuals).
If, after all else fails:
The detector (receiver) lens should also be cleaned on a regular basis. Road dust and dirt (or worse!) can and will collect on the lens of even the best-designed product. Traffic signal detectors should be tested frequently, particularly during the warm weather months when thunderstorms are more common (nearby ground strikes can and will damage even the best protected electrical apparatus)
Safety Alert! NEVER “assume” that a preemption-equipped traffic signal is operating properly! The Confirmation Light (high intensity flood lamp that is often located near the detector on the traffic signal to alert the emergency vehicle driver that he has gained control of the intersection) may not be illuminating because the detector isn’t working!!! ALWAYS PROCEED WITH CAUTION!!! NEVER “ASSUME” THAT THE CONFIRMATION LIGHT IS BURNT OUT!!!
Do Infrared lenses affect range?
The short answer is “yes”, for maximum range remove the enternal IR filter.
Legal Alert! Some states restrict the use of specifically colored warning lights, including strobes, for specific purposes only. Please click here to go a chart for each state’s Department of Transportation website link
What About ‘Compatibility’? Will the MIRT work with 3M Opticom® and Tomar Strobecom® detectors?
Preemption-equipped traffic signals that are programmed to only respond to custom-encoded preemption transmitters will not work with any MIRT product at this time. However, the actual percentage of preemption-equipped intersections that only respond to custom-encoded transmitters is very small. Are there any negatives to preemption-equipped intersections that are programmed for “Restricted Access”? (meaning that only custom-encoded transmitters can activate them)
Yes. FAC of America does not offer transmitter ID encryption of its devices at this time due to the logistical problems and liability often created where such systems are deployed. If a preemption-equipped traffic signal is programmed so that it permits access only to predetermined vehicles, every single traffic signal within the territorial boundary of the equipped emergency vehicle must be similarly equipped.
The programming of traffic signal preemption detector electronics is almost never performed by the departments who must make use of them, making the logistics of maintaining such a system cumbersome, impractical, and very expensive - particularly when new vehicles are equipped with transmitters and every traffic signal must then be programmed to accept the new vehicles - logistical responsibilities that responding departments cannot directly control.
Liabilities arise when bordering departments, which may have vehicles equipped with preemption transmitters, cannot gain access to encrypted intersections or, worse, when it is “assumed” that access can be gained, creating a potentially high risk situation because the responding emergency vehicle driver believes that he/she has control and right-of-way through the intersection.
Will the use of the MIRT void other manufacturer’s warranties?
No. Legal precedents have actually been established that prevent marketplace competitors from even threatening to void warranties when competing or interactive devices can not be proven to “harm” the product under warranty.
What is the difference between “Low Priority” and “High Priority” preemption?
“Low Priority” is generally used by mass transit authorities to increase the time duration of green lights or and/or decrease the time duration of cross-traffic red lights. “High Priority” takes precedence over “Low Priority”, and the purpose is to secure control of the intersection by maintaining a single direction of traffic flow by holding the traffic signal green until the emergency vehicle has passed through that intersection. “Low Priority” is generally considered to be 10 hertz (10 flashes-per-second) while “High Priority” is 14 hertz. The MIRT is only available in “HIGH PRIORITY” 14 hertz.
Why is it necessary to execute a “Restricted Sale” Agreement?
FAC of America will not sell traffic control products to individuals that are not legally authorized to use the devices. However, we provide a “no obligation authorized distributor agreement”, that will qualify you to inventory and sell the MIRT to Authorized users, as determined by County, State and Federal laws.
The “Restricted Sale” agreement is a tool used by FAC of America to determine the authenticity of the buyer, and to prevent unauthorized individuals from illegally obtaining the product. We highly recommend that you take advantage of the huge opportunity to sell this cutting edge technology, that is the perfect answers for departments with limited budgets and so many more authorized users.
What are the state laws regarding the use of preemption transmitters?
Legal Alert!
Laws vary from state to state. Please follow the link to each state’s Department of Transportation website link (DOT links).
What is that white flood lamp on the traffic signal?
The “Confirmation Light” is primarily used to “confirm” that the intersection has been accessed by an approaching emergency vehicle. Individual state Departments of Transportation determine when the light actually illuminates, and if it flashes or not.
In most instances, the Confirmation Light will remain illuminated (or flash) until it no longer detects the preemption transmitter, which is usually because the emergency vehicle has passed through the intersection.
Why can’t I just flash my high beams real fast? ,
You can flash your high beams real fast - it just won’t activate modern optically-based preemption detectors!
3M Opticom® detectors (receivers) have advanced circuitry features which are only looking for the very brief flash of a strobe light, with a precisely timed interval between flashes. Headlamp high beams (any headlamps) turn off and on very slowly compared to strobe lights, and controlling the timing of a mechanical switch to precisely set the interval between flashes might be a fun way to exercise, but it is a waste of time if the objective is to activate preemption detectors.
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