Two-light traffic signals

From:

"The first electric traffic light had only red and green lights; it did not have a yellow light like modern-day traffic signals. Instead of a yellow light, it had a buzzer sound that was used to indicate that the signal would be changing soon."

Growing up, we had a variety of "traffic signals" -- including *single* lights. Note that a light can also FLASH -- which conveys additional meaning.

E.g., here, our left-turn arrows flash yellow while oncoming traffic has a solid green (we use a "lagging left" strategy). So, you can legally enter the intersection (for a left turn) and execute that turn

Well the first is pretty long ago. As I understand it two-lights were still being used in some smaller municipalities well into the 60s, even

The intersection in the center of the town I grew up in had a hanging flashing red/amber lamp well into the 70s until it was replaced with full signals around the year I was born. Second-hand info, obviously.

There are a few signals like this in MA but they're currently rare. More common in Rhode Island.

Usually you're either fortunate enough to have a fully protected green arrow in a dedicated left turn lane that then sequences back to solid yellow arrow and red, or yield on green and fight the yellow trap at "less congested" intersections with a single lane of traffic.

Sometimes the green arrow sequences to solid green at edge-case intersections.

There's always some confusion as to whether one can turn on a red arrow; at least in MA a red arrow is no different than a solid red signal for your lane (just implies thee are multiple lights for your direction of travel that are timed differently) so you can turn on a red arrow any time you can turn on a solid red.

Here's an ad for a two-light signal from 1944, this one has a brief all-dark period both directions in lieu of a yellow. Seems dangerous, maybe the switched over to green-red flash at night:

I know in olden times some three-light signals also changed to yellow in unison, prior to swapping green-red directions.

Hanging red/amber single-light flashers seem unpopular in my area now, probably due to maintenance cost. Most seem to have been replaced by something like a solar powered STOP sign with red LEDs for the side route, and the same but CAUTION for the main route.

And flashing red?

Here, in San Mateo, at night, El Camino Real (main road in spanish) is always flashing red. I assume it's merger beware. Ongoing traffic don't even slow down.

It was common for a hanging flashing red (with flashing yellow on the cross street) to be present at intersections that were either obscured by flora or known to be "problematic" (folks ignoring the fact that there *might* be cross traffic present). I guess the thinking being that it is easier to KEEP a hanging light visible than it is to HOPE folks will see stop signs that can easily be overgrown by shrubbery.

It was also common to see a hanging flashing yellow (*two* sided) on very narrow roads -- e.g., crossing single-lane bridges off the beaten track. Again, I think the light was just used to stress the point.

I remember seeing two-light (red and green both went on rather than having a yellow) in NYC ca. 1974.

I saw some like that, maybe late 60's, in some small town, maybe in Alabama. I think the whole thing had two light bulbs. Red was on top in one direction, bottom in the other.

That's okay for the early piss-ant roads where the speed limit was 15 MPH. NHTSA and its regulation changed all that- probably respecting information on 100,000 intersection crash fatalities. These days a yellow is required and its duration is supposed to be 1 second per 10 MPH of the road speed limit, which I find rarely observed. Yellow is almost always too short.

In NYC they were both on in the rare instance that was in place.

In the other possibility, I think you mean both go dark in one direction while the other direction is red.

Here's an ad for a two light, it says "when the red STOP goes out there is an interval of about 3 seconds before the green GO lights up, and vice versa."

That sounds to me like the whole signal goes dark for 3 seconds, but maybe I'm misunderstanding the phasing.

Ah, here's an example of it operating: