Criticism
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.
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.
Read more about this topic: 3M High Visibility Signals
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