A question when traffic lights switch to flashing red/flashing yellow mode

[paulthemapguy]

I understand what you are getting at, one direction, suppose N/S is the "major street" and suppose E/W is the "minor street", this sounds good in theory, but what about when you get to situations where you have two streets that are equally "major". Think about when the two main perpendicular streets in such a town meet, who gets the flashing yellow and who gets the flashing red. Hence this is why some intersections in places that switch to flashing yellow/flashing red mode have intersections with all flashing reds.

If traffic counts are equal, choose one direction at random. Its still better for traffic then the 4 way stop and eliminates the confusion.

Agreed.  Unless you have long-range detection loops, which isn't likely because that means agencies would have to spend extra money.  If it's an intersection where every leg is a low-volume urban street, however, I can see reason for a 4-way stop there, too.

I just got back from Omaha.  Driving around late at night revealed that many signals switch to flashing yellow/red operation after hours.  This was new to me, as all signals in Illinois require 24-hour operation, if I'm not mistaken.

[kphoger]

all signals in Illinois require 24-hour operation, if I'm not mistaken.

I've lived in more than one town in Illinois that switches at least some stoplights to flash mode late at night.  Specifically Wheaton (2000—2006) and Herrin (2006-2008).

[Big John]

all signals in Illinois require 24-hour operation, if I'm not mistaken.

I've lived in more than one town in Illinois that switches at least some stoplights to flash mode late at night.  Specifically Wheaton (2000—2006) and Herrin (2006-2008).

This was a while back, but IDOT had a policy of it the signals went into flash mode, all sides would see a flashing red.  Not sure if this is still the case.

[kphoger]

all signals in Illinois require 24-hour operation, if I'm not mistaken.

I've lived in more than one town in Illinois that switches at least some stoplights to flash mode late at night.  Specifically Wheaton (2000—2006) and Herrin (2006-2008).

This was a while back, but IDOT had a policy of it the signals went into flash mode, all sides would see a flashing red.  Not sure if this is still the case.

The ones I remember were all red/red.

[jeffandnicole]

Why would someone thing flashing red meant "all-way stop" instead of simply "stop"?

Driver expectancy. Per:

Around here, they're almost always on rural roads, often with the other road having flashing yellow.

Whereas urban intersections will have an all-read flash sequence, converting it to an AWS in emergency. Therefore the situation is being applied inconsistently. And inconsistency is the worst situation possible when it comes to human factors in traffic engineering.

Right, mid-block U-turns are the kind of thing that will get you a ticket around here.

Well, changing one piece of ill-conceived legislation is far easier than changing signals across the board.   

Around here urban intersections still have one direction flashing yellow and one red. Seems like the easier solution would be to switch all intersections to have one direction to flashing yellow, as flashing red in all directions will cause delays, waste gas, and is all around less efficient.

I understand what you are getting at, one direction, suppose N/S is the "major street" and suppose E/W is the "minor street", this sounds good in theory, but what about when you get to situations where you have two streets that are equally "major". Think about when the two main perpendicular streets in such a town meet, who gets the flashing yellow and who gets the flashing red. Hence this is why some intersections in places that switch to flashing yellow/flashing red mode have intersections with all flashing reds.

If traffic counts are equal, choose one direction at random. Its still better for traffic then the 4 way stop and eliminates the confusion.

No, no, no.

Imagine if there was an accident at the intersection.  They review the intersection and determine why one direction was flashing yellow and the other red.  I don't think "Oh, we flipped a coin.  Best out of 5 won." is going to fly in any engineering school or court.

Besides, the chances of the intersections having an equal amount of traffic late at night is quite low.  In that case, you probably want the light running normal operation 24/7.

[UCFKnights]

Why would someone thing flashing red meant "all-way stop" instead of simply "stop"?

Driver expectancy. Per:

Around here, they're almost always on rural roads, often with the other road having flashing yellow.

Whereas urban intersections will have an all-read flash sequence, converting it to an AWS in emergency. Therefore the situation is being applied inconsistently. And inconsistency is the worst situation possible when it comes to human factors in traffic engineering.

Right, mid-block U-turns are the kind of thing that will get you a ticket around here.

Well, changing one piece of ill-conceived legislation is far easier than changing signals across the board.   

Around here urban intersections still have one direction flashing yellow and one red. Seems like the easier solution would be to switch all intersections to have one direction to flashing yellow, as flashing red in all directions will cause delays, waste gas, and is all around less efficient.

I understand what you are getting at, one direction, suppose N/S is the "major street" and suppose E/W is the "minor street", this sounds good in theory, but what about when you get to situations where you have two streets that are equally "major". Think about when the two main perpendicular streets in such a town meet, who gets the flashing yellow and who gets the flashing red. Hence this is why some intersections in places that switch to flashing yellow/flashing red mode have intersections with all flashing reds.

If traffic counts are equal, choose one direction at random. Its still better for traffic then the 4 way stop and eliminates the confusion.

No, no, no.

Imagine if there was an accident at the intersection.  They review the intersection and determine why one direction was flashing yellow and the other red.  I don't think "Oh, we flipped a coin.  Best out of 5 won." is going to fly in any engineering school or court.

Besides, the chances of the intersections having an equal amount of traffic late at night is quite low.  In that case, you probably want the light running normal operation 24/7.

Why would that matter? If there's a accident, why would they be investigating why one direction has a flasing yellow unless that somehow caused a problem? Either direction having a flashing yellow is perfectly valid from an engineering standpoint, and these random decisions are done all the time. Although I do agree that it is extremely unlikely the traffic counts are actually equal, some direction will be more popular.

[cbeach40]

Why would that matter? If there's a accident, why would they be investigating why one direction has a flasing yellow unless that somehow caused a problem?

To ensure that all responsible parties did everything they could reasonably do to prevent the accident. Making a random choice is not doing that.

Either direction having a flashing yellow is perfectly valid from an engineering standpoint,

If they both are equally valid for a yellow, then neither is valid for a flashing red.

and these random decisions are done all the time.

Not too often by engineers who want to keep being engineers. 

[roadfro]

If traffic counts are equal, choose one direction at random. Its still better for traffic then the 4 way stop and eliminates the confusion.

No, no, no.

Imagine if there was an accident at the intersection.  They review the intersection and determine why one direction was flashing yellow and the other red.  I don't think "Oh, we flipped a coin.  Best out of 5 won." is going to fly in any engineering school or court.

Why would that matter? If there's a accident, why would they be investigating why one direction has a flasing yellow unless that somehow caused a problem?

To ensure that all responsible parties did everything they could reasonably do to prevent the accident. Making a random choice is not doing that.

I would still think that picking the more major roadway, through route, or signed highway would be an easy justification. But even if the direction assigned flashing yellow were picked randomly, that basis alone wouldn't necessarily be at issue if a crash occurred at the intersection. For a typical intersection, there'd have to be some pretty unusual circumstances involved for the red/yellow flashing to contribute to crash causes or other safety problems.

In the instance of an incident review for a collision, especially if there is a party attempting to determine fault for said collision, the state of the signal (what is it displaying) is far more important that why the signal is in that state.

[jeffandnicole]

It would need to be a serious crash, such as a fatal, for them to investigate why a signal had a flash mode set for a certain direction.

If it's flashing yellow for the state and red for the county road, it's a pretty easy call.  But if it's two county roads, or two state roads, there would have to be a little more thought put into it.  Even if it's a judgment call, judgment is usually based on an engineer's professional opinion, which should take into account numerous conditions.  Random is just a 'throw the dart' type response to a legit traffic engineering decision, which would not be an advisable solution to a problem.

[UCFKnights]

Why would that matter? If there's a accident, why would they be investigating why one direction has a flasing yellow unless that somehow caused a problem?

To ensure that all responsible parties did everything they could reasonably do to prevent the accident. Making a random choice is not doing that.

Of course it is. As long as they follow all the engineering standards in determining that it is safe for either direction to have a flashing yellow light, and determining that there is no preference from an engineering standpoint that one should be selected over the other, making a random choice is doing just that and entirely safe. It would not get questioned (unless there is a new piece of information).

Even if it does get investigated, it is unlikely they are going to investigate "why was it set it to flashing yellow". They're going to investigate "was the signal set in a way that violates standards or guidelines", "did the configuration of this signal contribute to the accident", "is there a missing guideline or a unique situation here that was overlooked that would help prevent this from happening in the future". All the time when I ask engineers why they made some decision, they tell me "it feels right", or when I ask why not, they tell me "it doesn't feel right", and they don't get in trouble for that.

Either direction having a flashing yellow is perfectly valid from an engineering standpoint,

If they both are equally valid for a yellow, then neither is valid for a flashing red.

Sure, until you apply to flashing yellow to one direction, then the other direction becomes invalid for a flashing yellow and must go to flashing red.

and these random decisions are done all the time.

Not too often by engineers who want to keep being engineers. 

This is the real world, nearly every engineer I know (and there are plenty of them) make decisions without the facts all the time because things need to get done, and there isn't a rule for it (or they don't know the rule for it because there are so many rules). Decisions all the time are made randomly and these people are successful engineers. You ask them "why'd you put this pedestal here on this corner" and the answer is "well I needed to put it somewhere" and you ask them "can we move it here?" and the answer is "sure, no problem, I just placed it randomly within the bounds of the requirements". You give it to 10 engineers you're going to get 10 different locations. As long as an engineer picks one of the valid solutions that meets all of the criteria and standards, they'll continue to be engineers. (Hell, even if they don't pick a valid solution, as long as its not really bad, they'll continue to be engineers, it typically needs to rise to the level of willful violations or gross negligence to create a problem for them)

[jeffandnicole]

Why would that matter? If there's a accident, why would they be investigating why one direction has a flasing yellow unless that somehow caused a problem?

To ensure that all responsible parties did everything they could reasonably do to prevent the accident. Making a random choice is not doing that.

Of course it is. As long as they follow all the engineering standards in determining that it is safe for either direction to have a flashing yellow light, and determining that there is no preference from an engineering standpoint that one should be selected over the other, making a random choice is doing just that and entirely safe. It would not get questioned (unless there is a new piece of information).

In court, EVERYTHING is allowed to be questioned, unless the judge throws it out. 

All the time when I ask engineers why they made some decision, they tell me "it feels right", or when I ask why not, they tell me "it doesn't feel right", and they don't get in trouble for that.

I'm not sure exactly what you do, but why would they get in trouble answering a question you asked?   And being the vague comments, here, I wouldn't know what this could be in reference to.  I can tell you that an engineer sitting in court, when asked "Why was the traffic signal placed in such a position", "Because it felt right" would not benefit the defense's case.

and these random decisions are done all the time.

Not too often by engineers who want to keep being engineers. 

This is the real world, nearly every engineer I know (and there are plenty of them) make decisions without the facts all the time because things need to get done, and there isn't a rule for it (or they don't know the rule for it because there are so many rules). Decisions all the time are made randomly and these people are successful engineers. You ask them "why'd you put this pedestal here on this corner" and the answer is "well I needed to put it somewhere" and you ask them "can we move it here?" and the answer is "sure, no problem, I just placed it randomly within the bounds of the requirements".

I don't believe any of this.  You mean they just put a pedestal wherever they want, without regards to there being drainage pipes, electrical, trees, power lines, sidewalks, light fixtures, etc?

And they'll make decisions ignoring rules and laws because they don't know them?

You give it to 10 engineers you're going to get 10 different locations. As long as an engineer picks one of the valid solutions that meets all of the criteria and standards, they'll continue to be engineers.

This is correct.  But if something goes wrong, they're going to speak to the engineer who's solution they went with.  The other 9 ultimately had nothing to do with it.

(Hell, even if they don't pick a valid solution, as long as its not really bad, they'll continue to be engineers, it typically needs to rise to the level of willful violations or gross negligence to create a problem for them)

Isn't "not picking a valid solution" equal to a willful violation or gross negligence?  Sure, maybe they'll keep their license, but that doesn't mean they're not at fault.

[roadman65]

I wish that some signals would go back to that switching to flash mode in non peak travel times.  We used to do that here in Orlando, but recently they seem to be all 24/7 operating.

[paulthemapguy]

Traffic counts are so detailed that it's almost impossible to find two segments next to each other that will have the same exact ADT.  No engineers are picking approaches at random.  And even if they did, the engineers would bullshit a technical explanation for what they did anyway.

[UCFKnights]

I don't believe any of this.  You mean they just put a pedestal wherever they want, without regards to there being drainage pipes, electrical, trees, power lines, sidewalks, light fixtures, etc?

Of course not, that is not within the bounds of the requirements, I wrote that in the sentence you quoted. There is always separation requirements between all of the things you mentioned, so violating those requirements would not be permitted. But once all of those things are cleared, there is still often a ton of choice where to put it. Do we put it on the north side of this intersection? The south side? 50 ft away? 75 ft away? 78 ft away? As long as there is no preference, guideline, or rule being violated, any of those choices could be perfectly acceptable and the engineer is free to do it randomly. Obviously if there is a tree 50 ft away that will interfere, that would not be acceptable. Anything that violates a rule or guideline when it is possible to follow said rule or guidelines removes that choice. The real world isn't black and white like you make it seem.

[jeffandnicole]

I don't believe any of this.  You mean they just put a pedestal wherever they want, without regards to there being drainage pipes, electrical, trees, power lines, sidewalks, light fixtures, etc?

Of course not, that is not within the bounds of the requirements, I wrote that in the sentence you quoted. There is always separation requirements between all of the things you mentioned, so violating those requirements would not be permitted. But once all of those things are cleared, there is still often a ton of choice where to put it. Do we put it on the north side of this intersection? The south side? 50 ft away? 75 ft away? 78 ft away? As long as there is no preference, guideline, or rule being violated, any of those choices could be perfectly acceptable and the engineer is free to do it randomly. Obviously if there is a tree 50 ft away that will interfere, that would not be acceptable. Anything that violates a rule or guideline when it is possible to follow said rule or guidelines removes that choice. The real world isn't black and white like you make it seem.

Still not correct.  If you put it 10 feet away from the curb, you'll need a certain length mast.  If you put it 20 feet away from the curb, you'll need a different length mast.  Depending on state guidelines, a 20 foot mast can be made of a certain type of material, but a 30 foot mast may need a different type of material.

10 or 20 feet, or 50 or 75 feet, means you have to run wiring for a different length.

How about pedestrian buttons and signals?  If the pole is 1 foot away from the sidewalk, you can put the ped button on the post.  If the pole is 10 feet away from the sidewalk, it's not useable for the ped button.

Again, there's nothing random about it.  Everything they do has a reason.  And everything they do affects other things related to the intersection.

And if you want to get down to it, if one is looking at rules and guidelines, then they're not making random decisions.  They have justified a location based on the conditions present.

[paulthemapguy]

I don't believe any of this.  You mean they just put a pedestal wherever they want, without regards to there being drainage pipes, electrical, trees, power lines, sidewalks, light fixtures, etc?

Of course not, that is not within the bounds of the requirements, I wrote that in the sentence you quoted. There is always separation requirements between all of the things you mentioned, so violating those requirements would not be permitted. But once all of those things are cleared, there is still often a ton of choice where to put it. Do we put it on the north side of this intersection? The south side? 50 ft away? 75 ft away? 78 ft away? As long as there is no preference, guideline, or rule being violated, any of those choices could be perfectly acceptable and the engineer is free to do it randomly. Obviously if there is a tree 50 ft away that will interfere, that would not be acceptable. Anything that violates a rule or guideline when it is possible to follow said rule or guidelines removes that choice. The real world isn't black and white like you make it seem.

I think "randomly" isn't the word you are looking for.
Signalized intersections are carefully planned with everything laid out on roadway plans by Phase II engineers.  This includes all signals, masts, handholes, and--yes, the control cabinet (we call it "tha cabinet").  Engineers also have to decide on the use of a backup power supply, where to place that, detector loops or infrared cameras, signal head placement etc. etc.  But pedestals/cabinets are laid out with just as much consideration as the signal structures themselves.  Keep in mind that all the wires from the detector loops will have to tie into a handhole or cabinet, so engineers will want to minimize the lengths of wire to keep things cost-efficient.  As for navigating around utilities, roadway plans are often created with limited knowledge of joint utility locations, so utility companies are typically contacted by the Phase III engineers (the ones who oversee the actual construction process) and informed that they need to move their wires, cables, powerlines, gas mains, etc. out of the way of the new construction.  That's the way I've seen it anyway...as an actual Phase III roadway engineer.

[8.Lug]

I haven't read all the posts in this so I don't know if it's been said - but there will never be a four-way flashing yellow. It will either be a four-way red, or two-way yellow with a two-way red crossing.

[Jet380]

I haven't read all the posts in this so I don't know if it's been said - but there will never be a four-way flashing yellow. It will either be a four-way red, or two-way yellow with a two-way red crossing.

But if you're driving overseas don't assume it will be the same! Australia and (I think) most European countries use 4-way flashing yellow only.

[jeffandnicole]

I haven't read all the posts in this so I don't know if it's been said - but there will never be a four-way flashing yellow. It will either be a four-way red, or two-way yellow with a two-way red crossing.

I once saw a 3 way flashing yellow at a temp signal off of Exit 56 on NJ's I-295.  Clearly an error. Yet, it remained throughout the few weeks (up to a month) is was active.  Never once heard of an incident and nothing was in the news about it.  In this case, those using the offramp had to turn left here (right turns split off prior to a porkchop island), so they were the ones supposed to stop, and apparently they did!

[8.Lug]

I haven't read all the posts in this so I don't know if it's been said - but there will never be a four-way flashing yellow. It will either be a four-way red, or two-way yellow with a two-way red crossing.

But if you're driving overseas don't assume it will be the same! Australia and (I think) most European countries use 4-way flashing yellow only.

You guys don't even know what side of the road you're supposed to drive on!

I jest. I actually do know it's us that's on the wrong side of the road. (Driving on the left actually came about from coming up along side someone's right side to extend your right hand to greet them, which started LONG before cars even existed).

[jeffandnicole]

Since it's kinda relevant, here's plans I came across online for a new traffic light at an intersection in Delaware.  While you don't see and hear the thought that went into where the placement of the light should go, you can see the detail presented that indicates how much they look at. http://www.deldot.gov/information/projects/centreville_safety_study/pdf/SR52_OwlsNest_TwaddellMill.pdf

[CNGL-Leudimin]

I haven't read all the posts in this so I don't know if it's been said - but there will never be a four-way flashing yellow. It will either be a four-way red, or two-way yellow with a two-way red crossing.

Obviously you have never been to this part of the world. We only have flashing yellow. No flashing red (Which is Chinese to me), we'll put a Stop sign with the flashing yellow for the same meaning.

[US 81]

I've thought of this every so often. Some towns switch to red/yellow, others red/red, still others offer a mixed bag. If you can't see the cross-traffic signals, then there's no foolproof way knowing. As much as I dislike stoplights, I'd rather signals operate 24/7 than not know whether I can safely go or not.

The flash at night is not uncommon in Texas. I don't remember ever being at an intersection where I couldn't see the cross-street signals, but in this thread it sounds like that must be a problem in some areas. I'm wondering why. Are the signal hoods larger, maybe obstructing the view? Signal placement? Intersection geometrics?

[8.Lug]

I haven't read all the posts in this so I don't know if it's been said - but there will never be a four-way flashing yellow. It will either be a four-way red, or two-way yellow with a two-way red crossing.

Obviously you have never been to this part of the world. We only have flashing yellow. No flashing red (Which is Chinese to me), we'll put a Stop sign with the flashing yellow for the same meaning.

Definitely haven't been off the continent, seems kind of weird so many people here aren't from North America. But regarding your stop-sign comment - you can't have a stop sign and a full 3-color signal, it doesn't make sense. This thread is about lights that change from normal 3-color operation during the day, to flashing lights at night.

[jjakucyk]

Cincinnati has many signals that go into flashing mode at 10:00 or 11:00 at night.  That's the key, AT NIGHT, you know when it's DARK out, so there's no problem coming to a flashing red and seeing that the cross street has a flashing yellow.  If it's a busier intersection with turn phases, or complicated geometry then it stays in RYG mode 24/7, but otherwise it's really not that complicated to give the main street a flashing yellow and the side street flashing red late at night.