3M

Some really random text about 3M's traffic division here. (Also, be sure to reference that they made a bi-modal, time-programmable sign, too!)
This page is a work in progress!

Products

Programmable Visibility Signals

Vehicle Signals (12")

M-131 Programmable Visibility Signal

3M M-131 signal

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3M M-131 signal

Info I have saved on 3Ms, feel free to rip apart, correct, reword, whatever. I think Andrew's 3M might be the best for pictures. It's the cleanest and has the least surrounding clutter. Both a front picture and a back picture would be ideal. -Pyth

3M, the same company that makes well-known everyday products such as Scotch tape, entered the traffic control industry in 1969 with High-Visibility signals. These lights were unlike any other at the time in both design and operation. They featured PAR-46 lamps in the back of the signal, with an opening back housing that had an auto-disconnect to prevent electrical shock. This light would shine through multiple layers, which helped prevent a condition known as the 'sun phantom effect', where a signal would appear to be lit in all 3 indications during sunrise or sunset. The unique signal build also offered 'programmable visibility', where a technician could mask off parts of the road the signal faced so only certain lanes or areas saw the signal indication, while masked off areas saw the signal as off or very very dimly lit. At a time before louvers, this was very helpful in congested or crammed areas where drivers could be confused or overwhelmed by the number of signals lit. This unique feature came at it's own cost, however. A 3-section M-131, the most common model, weighs in at around 65 pounds, whereas the average 3-section 12" head comes in at around 40 pounds. Also, as mentioned, the M-131 uses PAR-46 lamps, which have much shorter lives than the average signal bulbs, and cost considerably more each. The PAR-46 bulbs also get incredibly hot after being on for a while, which is an inconvenience for collectors and field technicians. McCain produces a near-identical line of High-Visiblity Signals as well, which are understood to cost less but weigh around 80 pounds per 3-section head. 3M stopped producing this line in 2007, due to decreasing orders. Many collectors like to have at least one of these signals due to their unusual design.

LED inserts are offered by third party manufacturers (link to Electrotech and whoever else made them), but they usually require the removal of the photocell dimming unit to ensure proper function.

Signal Enlargers

Signal enlarges are attachments mounted on a signal door that expand to fit a larger lens. Around the early 60s, larger signal indications were becoming more popular because visibility was becoming a greater concern. Installing enlargers on a signal was cheaper and easier than replacing it.
3M made 3 lines of signal enlargers; for vehicle signals, round-lens pedestrian signals, and square-lens pedestrian signals.

This image is from the 1975 3M catalog in the document archive shows the 812 (top) & 810 (bottom) enlargers.

Vehicle Signal to Vehicle Signal

SA-812

The enlarger mounts where the visor would go on the signal's door. It is essentially a box that expands around an 8-inch lens to fit a door with a 12-inch lens.
The signal's original 8-inch lens is replaced with a glass diffusing lens. The enlarger is attached in the place of the visor. It is octagon-shaped where it attaches to the door; as it extends outward, the slanted sides (which are triangle-shaped) become the corners of the square-shaped front. A square lens slides into the lens holder/front door of the unit, which has a 12" circular hole for the indication to shine through. The door then simply slides into place on the front of the enlarger.
With this setup, the light shines through the 8" lens, into the enlarger and out the 12" lens, generating a larger and more visible indication with the same amount of light and without having to replace the signal.
3M specifically noted that these enlargers would not fit Eagle Durasig signals or any TSI signals. They also offered special clips to use when mounting on Crouse-Hinds signals.

SA-810

If enlargers need to be used on two consecutive sections of a signal (for example, the green indications on a 4-section R–Y–G–GA signal), there would not be enough space. The SA-812 12" enlarger would extend slightly over both sections around it in order to... well, enlarge... and you would not be able to fit a second one beneath it.
That is what the SA-810 is for; it is designed specifically to fit under an SA-812. It only expands to 10"x12" (as opposed to 12"x12"), and bends slightly downward, around the SA-812.
It's exterior design, besides the height and curvature, is similar to the SA-812.
Due to the irregular lens size, they were only available with green left or right arrows.

Vehicle Signal to Pedestrian Signal

Though the 3M catalog specifically says these "are adapters to enlarge 8" vehicle signals to 12" pedestrian signals", they were most likely designed for round-lens WAIT-WALK pedestrian signals.

SA-812DW

This enlarger uses the same body as the SA-812 with the lens & door of a SA-912.

SA-810W

This enlarger uses the same body as the SA-810 with the lens & door of a SA-910.

This image from http://www.stamfordadvocate.com shows a pedestrian signal with 3M enlargers in Washington D.C.
It has since been removed.
Click the image to enlarge it.