M-131 Signal
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.
Read more about this topic: 3M High Visibility Signals
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