The introduction of the overlap in New York City

[M3019C LPS20]

In 1952, the city of New York introduced a new form of caution for its two-section (red and green) traffic signals, in which soon became permanent. Prior to this time, the original indication was a dark out period, and both signal indications appeared unlit for a handful of seconds. The new overlap, in which both the red and green signal indications appear lit momentarily, effectively altered a motorist's initial reaction, and, in turn, significantly decreased sudden stops and accidents. The article from the New York Times (see below) discusses this change in New York City's traffic control system.

[agentsteel53]

the original indication was a dark out period,

I think I hate dark traffic lights more than just about any other traffic signal misdevelopment.  I always have to think "is this a dead signal, or one that hasn't been activated yet?  if so, is this one of those places where people treat it as a 4-way stop?  or will the guy behind me just rear-end me if I try it?" 

the worst is once driving around at night in rural Alabama, and coming up on an ancient signal (so old that, indeed, it did not have a yellow phase - just red and green bulbs) that looked like it had not been functional for at least 60 years...

... with the sheriff behind us.

we stopped, then went again.  we did not get pulled over.

[lepidopteran]

Exactly once, I saw the New York red-green overlap on a 2-section signal -- while it was turning green!  I suspect that was a malfunction.

[M3019C LPS20]

Exactly once, I saw the New York red-green overlap on a 2-section signal -- while it was turning green!  I suspect that was a malfunction.

Indeed a malfunction. In New York City, they were controlled by electro-mechanical signal controllers, so it is not a surprise. Likely cause is the failure of the red indication's cam finger to open at a certain interval, in which cuts the power to it.