Blinking traffic lights at night

The local city and county keep the traffic lights running all night. That is, they do not change to blinking red late at night unlike many other cities.

I’ve always been under the impression that blinking was more efficient during the low traffic volumes at night. No one is stopped for a couple minutes at an empty intersection, and perhaps it is less costly in terms of electric usage. True, the red lights burn out more quickly, but the yellow and green less quickly.

Can anyone confirm or refute my impression? Assuming I am correct, I’d like to have some arguments to bring to the local governments to petition the change. Especially the electricity part, seeing as how the west coast is having energy problems. If the savings are significant, that by itself might be all the argument I need.

My town (Spokane, WA) starts blinking around 1 or 2 AM, but most of the lights on major streets are blinking yellow instead of red. Our red lights are LEDs, so we’re already saving some energy there.

A blinking light will be on 50% of the time; a non-blinking light will be on 100% of the time. That looks like a 50% savings to me – more if you consider that a blinking red light is always using the cheaper LEDs, but a non-blinking light is using the LEDs less than half the time – and my guess is that the lights don’t burn out significantly faster.

I read years ago that Washington, DC stopped having blinking lights at night because too many people were running the blinking red lights and causing accidents. So it may be a public safety issue, if the people in your area weren’t stopping properly at the blinking reds.

      • That depends on the kind of public safety you’re talking about. Some places in the St Louis area went to blinking amber/red lights years back (the larger street gets the amber lights), because there was a sudden jump of carjackings at stoplights at two in the morning. - MC

What about the idea that it takes more energy to turn a light on repeatedly than to just keep it on continously? Or is this not true, or not relevant here?

Strange how hitting “Submit Reply” really wakes you up to how stupid your response is sometimes. Not relevant here clearly, but is this idea true generally speaking or was it one of those things adults told kids to stop them playing with the light switch?

Lights in DC have not been flashing for as long as I have been here - about 12 years.

Except whenever lightning strikes anywhere within a 100 mile radius or the wind blows a little too hard, then every light in the city goes to flashing red.

Even though I have a car, I walk almost everywhere because everything I need is 3, maybe 4 blocks away. So I can testify as a pedestrian that cars rarely stop for flashing red lights. I thinks it’s a mixture of ignorance & laziness. I bet lots of people think that flashing red lights mean caution just like flashing yellow.

Please enlighten a non-American? What do flashing red lights mean, anyway?

Over here in Germany, traffic lights occasionally flash amber (or yellow, if you prefer). They do draw attention to the intersection, but technically, they are to be ignored; precedence is according to the signs posted at the intersection (or right-before-left, if no signs are there, but I don’t recall to ever have seen an intersection equipped with traffic lights but not with signs).

I don’t know about todays computerized traffic signal systems, but for years they used to be set by a clockwork timer which specified the duration of the green, yellow, and red lights, and how long the duration of the intersection traffic flow in each direction was programmed
into the timer.
If a simple mechanical malfunction jammed the timer, the default program was initiated, with flashing yellow lights for the main traffic flow, red flashing lights for the minor flow.
The frequency of these defaults are indicative of your community’s maintainence department, or shall I say , lack thereof.

AFAIK, in most places it’s officially equivalent to a “Stop” sign. You must come to a full stop, but may proceed if there is no other traffic. Flashing yellow indicates “Caution.”

Two possible senarios:

  1. Flashing red in both (N-S & E-W) directions: Some fault has occured in the signaling equipment and the lights default to flashing red in all directions so that the fault, whatever it is, won’t cause a major accident by giving the green to both directions at once. You are supposed to treat a both-ways-flashing-red the same as a four way stop sign.

  2. Flashing red one direction, flashing yella the other: By order of the traffic engineers, signals can be set to flash in this manner whenever traffic conditions are light enough. The flashing yellow is a “proceed with caution” with the understanding that the opposing traffic has the flashing red. The flashing red means STOP and yield to all other directions of traffic. You may proceed when it is clear to do so.

Yesterday I passed through the intersection of Winston Churchill Blvd (4 lanes) and Highway 5 (6 lanes at that point) in Mississauga, Ontaro, where the lights were blinking red for the four-lane road, and solid green for the six-lane road. This was equivalent to a minor side street intersecting with stop signs…

This was clearly not a normal situation though; police were directing traffic through the intersection. Otherwise, traffic on Winston Churchill Blvd would not have had a chance to cross the intersection at all: Highway 5 is very busy.

In the US, a flashing yellow light at an intersection is meant to signal use of caution and yielding right of way when appropriate. A flashing red is the same as a stop sign. In my small town there isn’t much traffic after dark so you can pretty much cruise through flashing yellow. I don’t see flashing red at all. Flashing yellow can happen if a light is malfunctioning or purposely disabled; in either case there is a traffic cop directing things, sooner or later.


Here is Cecil on the cost effectiveness of turning lights on and off. It doesn’t quite answer your question about blinking traffic lights, but it’s a start.

Thanks for the replies, everyone.

As far as burning out sooner, I was assuming incandescent lights. While they may burn less power or maybe about the same (the inrush current Cecil refers to would make up for the time off), I expect that cycling the power periodically would put additional thermal stress on the filaments. So they would likely burn out sooner.

I wasn’t aware that traffic lights used LEDs (although if they didn’t, I would wonder why not). And not just for red, you can get LEDs in a variety of colors these days.

Based on my bicycle’s tail light battery lifetime, I’d say that blinking LEDs definitely save power. LEDs definitely have a longer lifetime than incandescents, even with blinking.

This thread brings back memories of waiting at one particular red light every morning at 5:00 AM on the way to crew practice. Never any cross traffic, just that the city of Troy has no idea that it might be a good idea to not use the same timing scheme 24 hours a day.

Back home in Boston, blinking red and yellow lights are used late at night.