3M High Visibility Signals

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A 3M Model 131 signal on display in a private traffic signal collection.

3M High Visibility Signals were a line of traffic signal products produced by the 3M Company from 1969 to 2007. The flagship of the product line was the 3M Model 131 High Visibility Signal.


3M branched off into the traffic signal industry partly as the result of product innovation and secondly as the result of an increase in complex intersections requiring specific traffic control. In late 1964, 3M began developing a line of beacon-type devices that were designed to feature the capability of being "optically limited" to a certain viewing area. The original design, invented by Roger H. Appledorn, was filed with the United States Patent Office on August 10, 1966. The original design consisted of a beacon-type device utilizing a fresnel lens, and several different combinations of light sources (the original source of light being a flashlight bulb), and all featured a light diffusing method and a method of masking the signal. In the patent application, Appledorn described the device as being able to be used as a traffic signal device, an airport beacon lamp, as well as a water navigation aid. After the patent was filed, 3M further enhanced the development, focusing solely on its traffic signal capabilities, and released the 3M Model 123.,[1] a prototype traffic signal that advertised the capability of being "visibly programmed" where certain lanes of traffic could view the indication. The prototype Model 123 was very crude in design, featuring a large door at the rear of the signal for replacing the lamp and allowing access to the signal's optics. In addition to masking the signal, it could also be vertically aimed about the axis via a series of alignment pins in 2-degree increments. These pins were located on the top of each signal housing,[2] and could allow the tilt to be adjusted from as little as zero to as much as ten degrees. Vertical axis alignment was performed initially by loosening the pins, and a retainer inside the signal housing. In July 1969, nearly three years after the patent was applied for, 3M was issued the patent on July 22, 1969.[3] After the patent was issued, 3M further enhanced the signal and introduced the Model 131, which featured a few enhancements over the 123 signal. Improvements over the 123 that were incorporated into the Model 131 signal were largely to make the signal easier to service. Those improvements included the ability to align the signal much more easily than the 123, and make signal maintenance easier.

M-131 Signal

3M traffic signals installed in Shelton, Washington. Standing off-axis from the intended viewing area, these signals appear to be "off" or invisible to adjacent lanes of traffic during the daytime. (A faint glow is present in the lit indication when viewed at night)
The same two signals above, taken in the signal's intended viewing area (a single lane of northbound traffic). Special light-diffusing optics and a colored fresnel lens create the indication.

The Model 131 traffic signal consisted of separately constructed signal housings. Each housing consisted of a rear bulb door that opened up allowing access to the lamp, as well as allowing the signal to be programmed. Each housing was lit by a 150-watt PAR lamp, which then passed through an opaque frosted glass "diffuser", and then a clear "optical limiter" lens. The optical limiter and diffuser were the primary components at the rear of the signal's optics (the optical limiter being the lens in which the signal's "masking" was performed), and at the front of the housing was a two-layer acrylic fresnel lens colored to meet ITE traffic signal lens specifications. Each section was joined to create a complete unit via alignment pin assemblies that allowed the traffic signal to be aimed vertically at two-degree increments beginning at zero degrees and a maximum of ten degrees (with specific settings for pedestal-mounted signals to be aimed at 4, and overhead-mounted signals to be aimed at eight degrees horizontal).

Applications of the 3M Model 131 were mainly focused towards complex intersections where specific control were required, including skewed intersections or complex multi-lane control. It was available in eight different mount configurations, as well as a multitude of display configurations.

Derivatives of the Model 131

Derivates of the M-131 signal included a pedestrian crosswalk signal, a bi-modal indication unit, and it was also used as lane-limiting devices at ferry docks, and as a special signal used by mass transit railroad operators.

Other products

In addition to the 3M Model 131, 3M also created a wide variety of retrofit applications for existing conventional incandescent traffic signal heads. Each product was slightly based on the M-131's design by utilizing a combination of light-diffusing optics and a colored fresnel lens.

Model SA130 8" lens adapters

The SA130 lens adapters utilized a miniature version of the 3M Model 131 optics package. The SA130 consisted of a housing designed to be installed in place of an eight-inch conventional traffic signal lens, and light was provided by the existing signal lamp and reflector, and passed through a frosted glass diffuser. Unlike the M-131, however, these didn't include a clear optical limiter; masking was done directly on the diffuser lens. At the front of each housing was a miniature version of a M-131 acrylic lens/visor assembly.

Model 150 High Visibility Lens System

The Model 150 consisted of a 12" fresnel lens and reflector bowl assembly that was designed to be installed in place of a conventional 12-inch traffic signal lens/lamp and reflector assembly. These were rarely used and were produced for a limited period of time, and were later pulled from the market due to a condition known as "sun phantom."

Model 812 Signal Enlarger

The Model 812 Signal Enlarger was invented by Roger Appledorn (inventor of the 3M Model 123 and 3M Model 131), and Gunnar Ljunkull. The patent, filed July 24, 1972,[4] and awarded on December 18, 1973, initially was designed to be a substitute for replacing then-conventional eight-inch signal heads. Each kit, essentially a retrofit application, consisted of a frosted diffuser lens that was installed in place of the existing eight-inch signal lens, and a bracket that consisted of a 12" fresnel lens that mounted to the existing signal via its visor fastening screws. The fresnel lens was typically clear while the frosted diffuser lens was tinted to meet ITE chromaticity and color output standards for traffic signals. Not very many of these Model 812 Signal Enlargers were ordered, largely because they could only be used on one indication in a typical traffic signal head. Some of them reside in traffic signal collections,[5] and a variant of the Model 812 was built for pedestrian signal indications.


While they were initially - and for a long time widely popular with many public agencies and traffic signal contractors, the 3M Model 131 is noted for being expensive to maintain. Unlike a typical traffic signal, which operates on a 110 V 8,000 hour life bulb identical to a household counterpart, the 3Ms operate on a 150 W PAR46 bulb similar to an old sealed-beam car headlamp bulb. Each bulb averages a 6,000 hour lifetime span. However, the bulbs are very expensive, and the bulbs are susceptible to early failure under induced vibration or moderate shock[no citations needed here].

They are also noted for being heavy. While an average 12-inch three-section traffic signal weighs around 35 pounds, the 3M is massive due to its construction and averages around 60 pounds (27 kg), increasing the strain on mounting hardware and making installation and removal difficult.

Finally, because off-axis visibility of the light is limited by design, when the light is slightly rotated due to high winds, weakening of support structure, or other factors, the light may no longer be visible to the intended drivers. The same limitation obtains when the light is mounted at an intersection with non-linear approaches; in such a case, although the light may be angled correctly for drivers actually entering the intersection, drivers on the curved approach to the intersection may not be able to perceive the state of the signal far enough in advance to safely adapt their speed.

As a result of those factors, many municipalities have begun removing them and replacing them with less expensive signals.[no citations needed here]

Discontinuation & Legacy

3M discontinued production of the Model 131 line in 2007 as the result of fewer orders for their signals. These fewer orders were due to initial purchase price (cost of a brand new 3M signal head in 2006 was approximately $2000 for a three-section head,[6]) and the fact that the bulb lifespan was only 6,000 hours. The decrease in orders was also due to competing traffic signal manufacturer McCain Traffic Solutions based in Vista, California. In the late 1990s, McCain developed and produced a programmable traffic signal of their own.[7] The "McCain Programmable Visibility Signal" was almost an exact copy of the 3M Model 131.[no citations needed here] Optical assemblies were almost exactly the same, with minor differences in signal housing body design. The cost of a McCain unit was substantially less, however, and municipalities began replacing 3Ms with the less-expensive McCain PV signal (despite the fact that a McCain Programmable Visibility Signal is around 10-15 pounds heavier than a 3M, and uses the same PAR46 lamp). McCain currentlyTemplate:When is the only producer of optically programmable traffic signals in the U.S.[no citations needed here]

Due to their unique design and shrinking numbers, the M-131 is highly sought after by traffic signal collectors.[no citations needed here]