Willis Lamm's
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| History of Traffic Signal Design |
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More Advances in Signal Design and Placement |
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| It was becoming increasingly clear to traffic safety engineers that standardization was necessary to avoid confusion among motorists, especially those from out of the area and unfamiliar with local signal configurations. Standards were established for lens design and brightness. Placement of colors was standardized with red being on the top and green on the bottom of vertically hung signals and red on the left and green on the right for horizontally hung signals. Lettered and other less conventional lens designs were dropped. Two color signals were being phased out and three color signals displayed green-yellow-red and directly back to green with no color overlaps. Protected left turns originally indicated by a simple green arrow that went dark after the protection phase ended had to be terminated with a yellow ball or arrow. Other "unusual" indications were also phased out. |
Protected left turns without separate |
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Other concerns were raised about a single signal head controlling multiple lanes of traffic. Some jurisdictions had six lane roads (three lanes in each direction) that were controlled by a single signal head. Even at smaller intersections there were concerns about the risks involved if a red bulb burned out.
Single signals once controlled multiple lanes of traffic.
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| On wider streets both of these problems were solved by installing at least two signal heads facing each direction. In 1949 Crouse-Hinds promoted the idea of double red lights for narrower streets (having only one lane in each direction) where a single signal head was adequate visibly but where a redundant red light should be provided to maintain protection in the event of a bulb failure. |
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| A standard was also established that on streets with speed limits higher than 40 MPH, red lenses should be 12 inches in diameter rather than the traditional 8-3/8 inches. The 12 inch lens could project a larger, brighter and more distinctive light, allowing drivers of vehicles traveling at faster speeds to recognize that the light was red from a longer distance away, ensuring safer stopping distances. Many single faced signals installed on boulevards were equipped with 12 inch red sections. Manufacturers designed adapters that could be installed on preexisting signals that did not have 12 inch red sections. |
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| The standards for indications that displayed arrows also increased to 12 inches since the arrow masks emitted less light and could be less distinguishable during bad weather conditions. Eventually many jurisdictions simply installed signals with all 12 inch lenses regardless as to their placement, posted road speeds, etc. |
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