The linked article below discusses the effectiveness of 'advisory' roads signs, such as the 'Children At Play' signs often seen around parks and neighborhood streets.
Here's a quote from the article: The Federal Highway Administration, in its Manual of Uniform Traffic
Control Devices, the sacred Ur-text of road signage, does not sanction
"Children at Play" signs. It notes: "The use of warning signs should be
kept to a minimum as the unnecessary use of warning signs tends to breed
disrespect for all signs...."
I think the same applies to 'daytime running lights' on cars. If a lot of cars have their headlights running in the daytime, then vehicles that need that extra bit of visibility -- such as ambulances and motorcycles -- become (in a sense) less noticeable since they no longer stand out from the crowd.
http://www.slate.com/id/2293460/
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