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

[Revive 755]

While brainstorming after reading a few posts, I think I know a solution that could possibly work to eliminate the ambiguity, unfortunately it would require a slight tweak of the rules.

Flashing Yellow - Proceed with caution (no change in meaning)
Flashing Red - Stop, this intersection is a FOUR WAY or ALL WAY stop
Flashing Red + Yellow - Stop, and proceed only if safe to do so, cross traffic has right of way

So if the flashing red indication fails for some reason there can be two perpendicular movements with flashing yellows?  It would be easier to phase in either permanent or blank out signs stating cross traffic does not stop. 

[Jet380]

A possible change that would not require a modification to the rules or the signal hardware would be to alter the rate and pattern of flash, for example:

Flashing yellow signal has short flashes with long gaps ie:
++____++____++____++____
Flashing red signal (cross traffic does not stop) remains unchanged ie:
++++____++++____++++____
Flashing red signal (cross traffic stops) has short flashes with short gaps ie:
++__++__++__++__++__++__

Leaving the 'cross traffic does not stop' pattern unchanged means that for signals that are not upgraded, drivers will assume the most restrictive signal. Adding a different pattern for flashing yellow would also be helpful for colourblind drivers who have difficulty distinguishing red and yellow at night.

[roadfro]

^ I don't think most motorists would pick up on the subtlety in the different flash patterns to make this viable. Besides, there are standards in the MUTCD that regulate the flash period of beacons and flashing signals (something like 'not less than 50 nor more than 60 flashes per minute').

[jeffandnicole]

A possible change that would not require a modification to the rules or the signal hardware would be to alter the rate and pattern of flash, for example:

Flashing yellow signal has short flashes with long gaps ie:
++____++____++____++____
Flashing red signal (cross traffic stops) has short flashes with short gaps ie:
++__++__++__++__++__++__

Leaving the 'cross traffic does not stop' pattern unchanged means that for signals that are not upgraded, drivers will assume the most restrictive signal. Adding a different pattern for flashing yellow would also be helpful for colourblind drivers who have difficulty distinguishing red and yellow at night.

We call these flash rates "malfunctions".   

[theline]

How about a sign near the signal with wording to this effect "WHEN FLASHING RED CROSS TRAFFIC DOES NOT STOP"?

[cbeach40]

How about a sign near the signal with wording to this effect "WHEN FLASHING RED CROSS TRAFFIC DOES NOT STOP"?

But then what happens when the signal has a fault and all red flash mode?

[theline]

How about a sign near the signal with wording to this effect "WHEN FLASHING RED CROSS TRAFFIC DOES NOT STOP"?

But then what happens when the signal has a fault and all red flash mode?

I'm thinking that's a rare and short-lived occurrence, while the red/yellow flashing mode happens for several hours each day. I'd suggest that it's better to have the assumption that the cross traffic doesn't stop when it does stop, rather than assuming it stops when it doesn't.

[Revive 755]

How about a sign near the signal with wording to this effect "WHEN FLASHING RED CROSS TRAFFIC DOES NOT STOP"?

But then what happens when the signal has a fault and all red flash mode?

In that case it should be a bit safer of a failure mode than potentially having two perpendicular movements flashing yellow.  There might be a few awkward moments where everyone at the intersection is trying to figure out what is going on, but any accidents should occur at lower speeds.

Isn't there an option with some signal controllers to make the conflict/hard flashing default to yellow/red?

[cbeach40]

How about a sign near the signal with wording to this effect "WHEN FLASHING RED CROSS TRAFFIC DOES NOT STOP"?

But then what happens when the signal has a fault and all red flash mode?

In that case it should be a bit safer of a failure mode than potentially having two perpendicular movements flashing yellow.  There might be a few awkward moments where everyone at the intersection is trying to figure out what is going on, but any accidents should occur at lower speeds.

If you've intentionally created an ambiguous situation, then you've failed at the one job you had.

Isn't there an option with some signal controllers to make the conflict/hard flashing default to yellow/red?

You could, but what happens if it fails during the PM peak? Then you've got a much, much bigger problem on your hand.




In terms of traffic engineering, this is all incredibly basic stuff. The absolutely first, and far most important rule is to never violate driver expectancy.

1. All red flash - only do this if drivers on all approaches can reasonably expect to stop
2. Red-yellow flash - only do this if A) drivers reasonably expect to stop on the one approach, B) drivers one the opposing road do not expect to stop, and C) drivers on the stopping road expect cross traffic to have right-of-way
3. Remain in cycling mode - if the above criteria are not met, do not mess with it.

Traffic signals are the one control device that has the least room for error. They also have the most black and white criteria. Something is either warranted or its not. Timing is either sufficient or it's not. It's not that hard.

[vdeane]

How about a sign near the signal with wording to this effect "WHEN FLASHING RED CROSS TRAFFIC DOES NOT STOP"?

But then what happens when the signal has a fault and all red flash mode?

In that case it should be a bit safer of a failure mode than potentially having two perpendicular movements flashing yellow.  There might be a few awkward moments where everyone at the intersection is trying to figure out what is going on, but any accidents should occur at lower speeds.

Isn't there an option with some signal controllers to make the conflict/hard flashing default to yellow/red?

Yes.  I know of one signal nearby (Forts Ferry/Wade) that has flashing yellow on one street and flashing red on the other in failure mode.

[jeffandnicole]

Almost every light I know of defaults to yellow/red flashing modes when not working properly. 

[MisterSG1]

So cbeach, I have a question, what happens at more complicated intersections if failure mode were to occur, I mean intersections which have fully protected left signals. Because if you ask me, any failure on a big intersection (like what I seen this morning at Leslie/Lake Shore, in this case all signals were simply off) can cause chaotic disorder at a major intersection.

Does every single signal flash red? Even the left turn ones?

I can recall back in 2002 on Huron Church Road in Windsor seeing one intersection displaying a flashing yellow ball for straight traffic and a flashing red ball for the fully protected left turn light, but what actually is the real standard for this.

[PHLBOS]

Almost every light I know of defaults to yellow/red flashing modes when not working properly. 

Many of the signals in Philadelphia (at least the Center City part of it) have an all-red flash mode.

[jakeroot]

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.

Many countries post secondary traffic control devices below the traffic signals, to indicate what the approaching driver should do, should the signals be dark, or, should they be flashing yellow. Typically, the other cross-road won't have any secondary traffic control device, because they're the priority road (the road with the most traffic), and if dark or flashing yellow, they can proceed without stopping.

As an example, the signal on the left has priority when dark or flashing yellow (the priority sign below the signal shows this); the signal on the right must stop when dark or flashing yellow:

[cbeach40]

So cbeach, I have a question, what happens at more complicated intersections if failure mode were to occur, I mean intersections which have fully protected left signals. Because if you ask me, any failure on a big intersection (like what I seen this morning at Leslie/Lake Shore, in this case all signals were simply off) can cause chaotic disorder at a major intersection.

Does every single signal flash red? Even the left turn ones?

Current Ontario standard is that signals with left turn arrows should not go into flash mode.


Per the OTM:

Standardized Flashing Operation

Traffic control signals that do not use left-turn arrow
heads (excluding types 8, 8A, 9 and 9A), may be
switched from their normal phase indication to
flashing operation. Three modes of flashing
operation are normally used:

- Start-up flash — the signals are commonly
started with flashing ambers on the main road
and flashing reds on the side roads.
- Emergency flash — when a conflict is detected,
the signals are commonly flashed in an all-red
or "red-red"  mode if the controller flashers have
that capability. The red-red mode has a safety
advantage over the red-amber mode (reds on
side road; ambers on main roads) but the red-amber
mode is an acceptable alternative and
is considered safer on roads with posted
speeds of 80 km/h and above and with light
side road traffic since fewer stops are required.
- Timed flash — the signals may be programmed
to operate in the red-red or red-amber mode
during various periods of the night or of the
week, for special events or during a Police
over-ride mode of operation.

It should be noted, however, that flashing operations
within a traffic control signal cabinet are generally
wired as either red-red or amber-red and the flash
circuit cannot be changed from one mode to
another without re-wiring the necessary circuits.

Planned flashing operation of signalized
intersections may be advantageous to traffic flow
under some specific and limited conditions. Flashing
operation may be of assistance in reducing vehicle
delay and stops in pretimed networks at locations
with poor signal spacing. Planned flash is only
applicable under conditions of very light minor street
traffic such as during the overnight period, or in
locations that have extended periods of low volume
such as accesses to an industrial area. Caution
should be used in the application of planned flashing
signal operation. It should only be used if:

- Sidestreet traffic is very light (less than
200 vph combined for both directions).
- The traffic signals operate fixed time (i.e., no
side street vehicular or pedestrian actuation).
- The planned flash mode is amber flash for the
main street, red flash for the side street.
- There is no emergency vehicle pre-emption
capability.
- Pedestrian volumes crossing the main street
during planned flashing period are very light.
- The major roadway is not channelized and has
no more than four lanes.

If planned signal flash is implemented, regular safety
reviews should be conducted to compare the
occurrence of collisions during the flash hours at
intersections with planned flash with similar
locations without planned flash.

The standard flashing red or flashing amber traffic
control signal indication shall be at a rate of not
more than 60 and not less than 50 ON and OFF
flashes per minute, with the length of each ON
period approximately equal to the length of each
OFF period. The flash rate is slower than that used
for flashing advance green indications.








Additionally MisterSG1, per our discussion at the Toronto meet this past weekend, flashing green ball was used in place of advance LT and Thru, the equivalent to a solid green ball+LT arrow. I'm sure ambiguity that you mentioned there was just one of the many reasons why that practice was recommended to be discontinued.

[cl94]

The above does not apply in the States. I'm not certain about what the MUTCD says (nor do I feel like digging through it), but from experience, I can say that fully protected signals can (and occasionally do) go into flash mode. Either the red arrow flashes or there is an otherwise-unused red or yellow ball that flashes. Examples of the latter include these in Burlington, Massachusetts and this one in Syracuse, New York. The latter very well might flash at night, but I have no intention to ever be in the area when it might ever go into flash mode (and I would not suggest that anyone tries). If you're familiar with Erie Boulevard in Syracuse, you know what I mean.

[jakeroot]

Either the red arrow flashes or there is an otherwise-unused red or yellow ball that flashes. Examples of the latter include these in Burlington, Massachusetts...

In that example, do both left turn lanes show a flashing orb? Does this qualify as a dual permissive left, at night?

[cl94]

Either the red arrow flashes or there is an otherwise-unused red or yellow ball that flashes. Examples of the latter include these in Burlington, Massachusetts...

In that example, do both left turn lanes show a flashing orb? Does this qualify as a dual permissive left, at night?

Knowing that intersection, I doubt it goes into flash mode at night (can someone in Eastern Massachusetts confirm this?). I assume it's there for emergencies. Every protected signal in the area has a normally-unused ball section.

[PurdueBill]

Either the red arrow flashes or there is an otherwise-unused red or yellow ball that flashes. Examples of the latter include these in Burlington, Massachusetts...

In that example, do both left turn lanes show a flashing orb? Does this qualify as a dual permissive left, at night?

Knowing that intersection, I doubt it goes into flash mode at night (can someone in Eastern Massachusetts confirm this?). I assume it's there for emergencies. Every protected signal in the area has a normally-unused ball section.

I can recall (over 20 years ago) such signals with the yellow ball in the left turn signal flashing on weekends even, with the yellow ball flashing.  It may not have been intended to be for non-emergency use, but practice was that it was used that way when the signals went on flashing for off-peak times.
The existence of flashing yellow arrow as something with an actual meaning now probably makes adding the yellow ball moot.

[JMoses24]

Here in Springdale, there's actually a signal 2 blocks away that, after a certain time of night, switches to a flashing red/flashing yellow configuration. The flashing red is on the main road, while the yellow is for the minor cross streets.