What are the rules around intersections with flashing lights?

Question

I will be travelling to the USA (from the UK) and renting a car. I have been looking into the various traffic laws and rules, signage etc. as well as potential routes to take for the journey, and I came across an intersection for which I don't understand the rules.

The intersection appears to be controlled by lights but there are only two lights, rather than three.

Aspect 1

Aspect 2

Aspect 3

These are the different aspects of the lights I can see from Street View (zoomed in). It's not quite clear to me whether the lights may be flashing or alternating, or even off occasionally (or if they're "off" because the camera caught them between aspects).

I am familiar with the rules around typical three-light traffic signals, single flashing yellow (proceed with caution) and single flashing red (treat as stop sign). What are the rules of these two-light signals?

Are there online resources which describe these rules? Are these types of traffic light only found in Alabama, or are they common across the country?

Answer 1

You probably won't find double flashing lights like this in any driver's manual or even online documentation. They're quite old and they never were common. What they were was confusing. I'm writing only from personal experience and memory, as I don't expect to be able to find anything online that old.

Both of the lights here flash yellow, and it is just a general caution signal. It does not necessarily mean you need to slow down or stop. On the cross road, both lights flash red, and there is also a stop sign, so traffic there must stop.

These caution lights were most likely installed because of the junction's slightly unusual layout. On the priority road, one lane is separated and does not stop; the other lane is exclusively for traffic turning onto or from the lower priority road. My best guess is: This T-junction is more like an italic T - the angle is close to 45 degrees! - and so there is much less visibility for people who wish to turn here. Thus the intersection most likely had a lot of accidents in the past, leading to this redesign with flashing caution lights and a separated lane for through traffic.

Answer 2

Are there online resources which describe these rules?

Each state has slightly different rules. The Department of Motor Vehicles (or similarly named agency) in each state typically produces a pamphlet (probably a PDF nowadays) that gives the most important rules, meant for new drivers studying to take the driving test in that state.

In Alabama the relevant agency is the Alabama Law Enforcement Agency, and they provide a Drives License Manual.

Are these types of traffic light only found in Alabama, or are they common across the country?

I've never seen it in Califoria or Illinois. But a single flashing yellow light is a fairly common indicator for "caution".

Edit

Having written that, later the same day I drove past this sign in California, which uses the same double flashing yellow lights to indicate caution, though not hung from wires above the middle of the street:

Answer 3

I have never seen a flashing traffic signal in the US with a red light below a yellow light so I believe both lights are alternating the same color. IThis type of signal is not in the Drivers License Manual for Alabama.

Using Aspect 1, and starting with the lanes from its point of view, the left lane is a left turn only lane. Drivers should stop due to the flashing red signal but can proceed whenever it's clear. The right lane is continuous flow--drivers there do not have to stop for the intersection.

The road entering from the left has a right-turn only lane with a Yield sign. The other lane is a left-turn only lane controlled by a stop sign.

The opposite direction has a dedicated right-turn only land controlled by a yield sign. The left lane is a through lane and has no markings on the road itself. Based on that, I think the light for this direction is flashing yellow. Be aware, but you shouldn't have to stop. For the original viewpoint (opposite direction to this), I believe the light is flashing red because the lane is a left-turn rather than a through lane.

Although the Alabama Motor Code section 32 5a-34 does state that if there's no line to stop at the intersection of the two roads.

Answer 4

A flashing yellow light means drivers should use caution in the area of the light. Since in one picture the upper light is on, and in another picture the lower light is on, most likely the flashing alternates between the top and bottom light to draw more attention.