Ever witnessed a prolonged yellow light?

[epzik8]

Did you ever see an unusually long yellow light during a traffic signal cycle? I was on Route 543 at Thomas Run/Southampton outside of Bel Air, Maryland and timed the yellow light for traffic going straight from Southampton onto Thomas Run, immediately before I, going southbound on MD-543, got the green light, as being about six seconds long. Most yellow lights I've seen last approximately three seconds. So it got me thinking if anyone else here has seen a yellow light during either a normal or non-normal cycle that they considered unusually long.

[jeffandnicole]

Did you ever see an unusually long yellow light during a traffic signal cycle? I was on Route 543 at Thomas Run/Southampton outside of Bel Air, Maryland and timed the yellow light for traffic going straight from Southampton onto Thomas Run, immediately before I, going southbound on MD-543, got the green light, as being about six seconds long. Most yellow lights I've seen last approximately three seconds. So it got me thinking if anyone else here has seen a yellow light during either a normal or non-normal cycle that they considered unusually long.

Most yellows you've seen aren't 3 seconds.  3 seconds is the absolute minimum, and should only be used on roadways of speeds/speed limits 30 mph or lower.  They are usually timed for 1 second per 10 mph, so a 50 mph roadway should have a 5 second yellow.  If you were on a 50 mph roadway and saw a 3 second yellow, almost guaranteed you would run the red before you had a chance to react to the light.

Most 55 mph or faster roadways should have 6 second yellows.  Some states may base it solely on the speed limit; other states will take into consideration average or 85th percentile speeds.

[Big John]

One intersection in Green Bay had the minor street (speed limit 30) have a 10-second yellow followed by a 5-second all red during evening hours.  Not sure why they did that but to irritate the stopped traffic on the major street.

[US 89]

On some expressways in my area, the yellow lights are at least six seconds long. I remember  specifically noticing it on the new Mountain View Corridor, where the speed limit is 65. Using the 1 second=10 mph rule, those lights would have been 6.5 seconds. I remember having trouble deciding whether or not I could stop in time. They do have those flashing "Prepare to Stop"  lights to help make those decisions easier.

[jakeroot]

One intersection in Green Bay had the minor street (speed limit 30) have a 10-second yellow followed by a 5-second all red during evening hours.

That is one of the most bizarre setups I've ever heard of. Is it still like this? A five second red is odd, but a ten second yellow is just...it has to be one the oddest things I've ever heard of.

[Brandon]

One intersection in Green Bay had the minor street (speed limit 30) have a 10-second yellow followed by a 5-second all red during evening hours.

That is one of the most bizarre setups I've ever heard of. Is it still like this? A five second red is odd, but a ten second yellow is just...it has to be one the oddest things I've ever heard of.

It looks like a five second delayed signal.  Most around here run about two seconds (all red, all directions).  Chicago has several (city operated, of course) that have a delay of zero seconds.

[roadfro]

MUTCD Guidance says the yellow change interval should be between 3 and 6 seconds.

Many agencies will use the ITE (Institute of Traffic Engineers) yellow change formula, which takes into account an assumed driver reaction time, the 85th percentile speed, an assumed deceleration rate of vehicles, and the grade of approach--this usually works out to the 3-6 second range.

[kphoger]

One intersection in Green Bay had the minor street (speed limit 30) have a 10-second yellow followed by a 5-second all red during evening hours.

That is one of the most bizarre setups I've ever heard of. Is it still like this? A five second red is odd, but a ten second yellow is just...it has to be one the oddest things I've ever heard of.

It looks like a five second delayed signal.  Most around here run about two seconds (all red, all directions).  Chicago has several (city operated, of course) that have a delay of zero seconds.

There used to be one in River Forest as well, as recently as 2000, with zero all-red phase.  Chicago Avenue and Thatcher.  It appears the light has been replaced since then, though.

[jakeroot]

One intersection in Green Bay had the minor street (speed limit 30) have a 10-second yellow followed by a 5-second all red during evening hours.

That is one of the most bizarre setups I've ever heard of. Is it still like this? A five second red is odd, but a ten second yellow is just...it has to be one the oddest things I've ever heard of.

It looks like a five second delayed signal.  Most around here run about two seconds (all red, all directions).  Chicago has several (city operated, of course) that have a delay of zero seconds.

There used to be one in River Forest as well, as recently as 2000, with zero all-red phase.  Chicago Avenue and Thatcher.  It appears the light has been replaced since then, though.

I'm not necessarily alarmed by long or non-existant all red phases (things that usually last about half a second around here), but I'm still trying to wrap my head around a ten second yellow. That's insane.

[kphoger]

One intersection in Green Bay had the minor street (speed limit 30) have a 10-second yellow followed by a 5-second all red during evening hours.

That is one of the most bizarre setups I've ever heard of. Is it still like this? A five second red is odd, but a ten second yellow is just...it has to be one the oddest things I've ever heard of.

It looks like a five second delayed signal.  Most around here run about two seconds (all red, all directions).  Chicago has several (city operated, of course) that have a delay of zero seconds.

There used to be one in River Forest as well, as recently as 2000, with zero all-red phase.  Chicago Avenue and Thatcher.  It appears the light has been replaced since then, though.

I'm not necessarily alarmed by long or non-existant all red phases (things that usually last about half a second around here), but I'm still trying to wrap my head around a ten second yellow. That's insane.

What are your thoughts about countries that employ a flashing green phase before the yellow phase?

[Big John]

One intersection in Green Bay had the minor street (speed limit 30) have a 10-second yellow followed by a 5-second all red during evening hours.

That is one of the most bizarre setups I've ever heard of. Is it still like this? A five second red is odd, but a ten second yellow is just...it has to be one the oddest things I've ever heard of.

That is no longer the case.  It is regular yellow and all-red now.  Not sure why they did the long times.

[traffic light guy]

Philly has a lot of elongated yellows, since most of their older equipment is still operated mechanically.

[doorknob60]

Ada County is pretty simple as far as I know. All yellows on roads <= 40 MPH are 4 seconds, and >= 45 MPH are 5 seconds. I don't know if there are any exceptions. Only exceptions I could imagine are SPUIs (but I think those just have a long all red phase) and ID-16 (the only road with lights and a 65 MPH speed limit, due to it being a freeway segment with temporary endings), though I think those follow the same rule still.

[jakeroot]

One thing that one of the counties I lived in did was made the distance of the solid white line separating lanes the length of where its okay to go through the yellow signal if your going the speed limit. So if a light turns yellow and you have a dashed line next to you separating lanes, you should stop, but if you have a solid line, you can make it through the light. I wish that was in MUTCD as most areas seem to use random lengths for those lines.

That's very cool. I'm used to seeing those lines used to indicate a ban on lane-changing near intersections and crosswalks (ubiquitous in Los Angeles, as well as Vancouver, BC), but never to indicate the safe point for yellow lights. I'd love to see that in the MUTCD.

[roadfro]

One thing that one of the counties I lived in did was made the distance of the solid white line separating lanes the length of where its okay to go through the yellow signal if your going the speed limit. So if a light turns yellow and you have a dashed line next to you separating lanes, you should stop, but if you have a solid line, you can make it through the light. I wish that was in MUTCD as most areas seem to use random lengths for those lines.

That's very cool. I'm used to seeing those lines used to indicate a ban on lane-changing near intersections and crosswalks (ubiquitous in Los Angeles, as well as Vancouver, BC), but never to indicate the safe point for yellow lights. I'd love to see that in the MUTCD.

This only works for drivers traveling at the exact speed in which the yellow time is calculated for though. So the downside is that if the signal settings are changed at all, the agency would have to modify the markings.

For example, if an agency sets the yellow according to ITE formula, then they later change the speed limit on the road, then they'd need to adjust the yellow time and subsequently change the dilemma zone markings.

[kphoger]

{b} 4-second flashing green, followed by 4-second yellow

{b} is a good middle-ground, but you'd still have people who will begin to slow when they see the flashing green. I'd also rather reserve the flashing green for pedestrian crossings (BC's adaptation), regardless if flashing green is allowed in the States.

A better idea, and something I see all the time in BC, is advanced "prepare to stop when flashing" signs. This is basically an MUTCD-compliant variation of {b}, but probably safer because it tells traffic from a ways out whether or not they're likely to make it (at the sign when it starts flashing?--you're good; still a good dozen meters away?--you're out), whereas a flashing green orb basically tempts drivers to run the light, because you're not sure how quickly you're going to reach the light (so speed up or prepare to stop).

My problem with the "prepare to stop when flashing" signs is that some of them just say "prepare to stop" and flash all the time.  So, when I see a sign like that, I'm never sure if I should even trust it or not.  There have been several times that I started to slow down at one of those signs, only to realize as I crossed the intersection at 10 mph under the limit (on a green light, with annoyed traffic passing me by) that there was no need to slow down at all because the lights always flash.  At least when the indication is part of the stoplight itself, you know darned well the light is about to change.

[jakeroot]

{b} 4-second flashing green, followed by 4-second yellow

{b} is a good middle-ground, but you'd still have people who will begin to slow when they see the flashing green. I'd also rather reserve the flashing green for pedestrian crossings (BC's adaptation), regardless if flashing green is allowed in the States.

A better idea, and something I see all the time in BC, is advanced "prepare to stop when flashing" signs. This is basically an MUTCD-compliant variation of {b}, but probably safer because it tells traffic from a ways out whether or not they're likely to make it (at the sign when it starts flashing?--you're good; still a good dozen meters away?--you're out), whereas a flashing green orb basically tempts drivers to run the light, because you're not sure how quickly you're going to reach the light (so speed up or prepare to stop).

My problem with the "prepare to stop when flashing" signs is that some of them just say "prepare to stop" and flash all the time.  So, when I see a sign like that, I'm never sure if I should even trust it or not.  There have been several times that I started to slow down at one of those signs, only to realize as I crossed the intersection at 10 mph under the limit (on a green light, with annoyed traffic passing me by) that there was no need to slow down at all because the lights always flash.  At least when the indication is part of the stoplight itself, you know darned well the light is about to change.

I don't think I've heard of that before. I know of two "signal ahead" signs that flash perpetually in my area (here and here), but they don't indicate to drivers that they are supposed to stop when they see the lights flashing (otherwise, drivers would forever be slowing for a light that isn't always changing). I do find these lights extremely annoying.

What I like are the signs that flash only when the lights are about to turn red, and when they're red. They're not strictly necessary on low-speed roads, but on high speed roads (such as the one I linked to in the first reply, or this one), they are extremely helpful. No surprising heavy braking.

[kphoger]

Obviously, if the lights weren't flashing earlier but I see them start to flash as I drive by, then I know it's a sign I should heed.  But, if I come upon a sign that already has its lights flashing, then there are two possibilities:  (1) the light is about to turn red, and the lights started flashing a little bit ago, or (2) those lights always flash, so who knows when the light will change.

[UCFKnights]

One thing that one of the counties I lived in did was made the distance of the solid white line separating lanes the length of where its okay to go through the yellow signal if your going the speed limit. So if a light turns yellow and you have a dashed line next to you separating lanes, you should stop, but if you have a solid line, you can make it through the light. I wish that was in MUTCD as most areas seem to use random lengths for those lines.

That's very cool. I'm used to seeing those lines used to indicate a ban on lane-changing near intersections and crosswalks (ubiquitous in Los Angeles, as well as Vancouver, BC), but never to indicate the safe point for yellow lights. I'd love to see that in the MUTCD.

This only works for drivers traveling at the exact speed in which the yellow time is calculated for though. So the downside is that if the signal settings are changed at all, the agency would have to modify the markings.

For example, if an agency sets the yellow according to ITE formula, then they later change the speed limit on the road, then they'd need to adjust the yellow time and subsequently change the dilemma zone markings.

They do have some tolerance built into the length formula so people don't accidentally run the red light, and I'd imagine there shouldn't be drastic changes in yellow times or speed limits without some construction. If its a minor change (like a half a second or 5mph speed change), the length wouldn't really change by that much and they could probably get away with not having any real consequence for having it slightly off.

[roadfro]

This only works for drivers traveling at the exact speed in which the yellow time is calculated for though. So the downside is that if the signal settings are changed at all, the agency would have to modify the markings.

For example, if an agency sets the yellow according to ITE formula, then they later change the speed limit on the road, then they'd need to adjust the yellow time and subsequently change the dilemma zone markings.

They do have some tolerance built into the length formula so people don't accidentally run the red light, and I'd imagine there shouldn't be drastic changes in yellow times or speed limits without some construction. If its a minor change (like a half a second or 5mph speed change), the length wouldn't really change by that much and they could probably get away with not having any real consequence for having it slightly off.

The ITE formula for a yellow clearance interval is y = t + [1.47*S / (2*a + 64.4*0.01G), where y is the yellow time, t is driver reaction time (common assumption is 1 sec), 1.47 is a conversion from mph to ft/sec, S is speed limit or 85th percentile speed in mph, a is deceleration rate (common assumption is 10 ft/s), 64.4 is twice the acceleration rate due to gravity, and G is the grade of the approach in percent.

With a flat grade, the yellow time for a 40mph roadway is 3.94 seconds, and it's 4.30 seconds for a 45mph road. So it's not a huge time difference.

We're talking about applying a pavement marking that indicates where it's okay to go through the yellow light when traveling the speed limit. For 40mph, the distance that marking is about 231 feet from the stop bar (distance = 1.47*S * y), whereas it's about 284 feet from the stop bar at 45mph. That's a difference of about 2-3 car lengths.

In a hypothetical scenario where the speed limit is reduced from 45 to 40 and the yellow time is decreased accordingly, a vehicle passing the unchanged "OK to pass on yellow" mark placed 284 feet from the stop bar would actually be about 50 feet upstream from the stop bar when the light turns red. That could open up some serious liability issues to the maintaining agency in the event of a collision...

[jakeroot]

We're talking about applying a pavement marking that indicates where it's okay to go through the yellow light when traveling the speed limit. For 40mph, the distance that marking is about 231 feet from the stop bar (distance = 1.47*S * y), whereas it's about 284 feet from the stop bar at 45mph. That's a difference of about 2-3 car lengths.

Even if that difference were smaller, a 230-280 ft-long solid line approaching an intersection is insanely long. Here's an example, made using the distance measuring tool built into Google Maps, showing a solid line of approximately 280 feet. Way longer than any solid line I've ever seen before (at least between two lanes going in the same direction). Most are about 80-100 feet:

[Scott5114]

{b} 4-second flashing green, followed by 4-second yellow

{b} is a good middle-ground, but you'd still have people who will begin to slow when they see the flashing green. I'd also rather reserve the flashing green for pedestrian crossings (BC's adaptation), regardless if flashing green is allowed in the States.

A better idea, and something I see all the time in BC, is advanced "prepare to stop when flashing" signs. This is basically an MUTCD-compliant variation of {b}, but probably safer because it tells traffic from a ways out whether or not they're likely to make it (at the sign when it starts flashing?--you're good; still a good dozen meters away?--you're out), whereas a flashing green orb basically tempts drivers to run the light, because you're not sure how quickly you're going to reach the light (so speed up or prepare to stop).

My problem with the "prepare to stop when flashing" signs is that some of them just say "prepare to stop" and flash all the time.  So, when I see a sign like that, I'm never sure if I should even trust it or not.  There have been several times that I started to slow down at one of those signs, only to realize as I crossed the intersection at 10 mph under the limit (on a green light, with annoyed traffic passing me by) that there was no need to slow down at all because the lights always flash.  At least when the indication is part of the stoplight itself, you know darned well the light is about to change.

I don't think I've heard of that before. I know of two "signal ahead" signs that flash perpetually in my area (here and here), but they don't indicate to drivers that they are supposed to stop when they see the lights flashing (otherwise, drivers would forever be slowing for a light that isn't always changing). I do find these lights extremely annoying.

What I like are the signs that flash only when the lights are about to turn red, and when they're red. They're not strictly necessary on low-speed roads, but on high speed roads (such as the one I linked to in the first reply, or this one), they are extremely helpful. No surprising heavy braking.

MoDOT eliminates any ambiguity by having their signs read "SIGNAL AHEAD", with a black panel at the top of the sign with red LEDs forming the word "RED" that flashes, thus forming the full legend "RED SIGNAL AHEAD". When the signal is green, of course, the word "RED" remains dark.

[jakeroot]

{b} 4-second flashing green, followed by 4-second yellow

{b} is a good middle-ground, but you'd still have people who will begin to slow when they see the flashing green. I'd also rather reserve the flashing green for pedestrian crossings (BC's adaptation), regardless if flashing green is allowed in the States.

A better idea, and something I see all the time in BC, is advanced "prepare to stop when flashing" signs. This is basically an MUTCD-compliant variation of {b}, but probably safer because it tells traffic from a ways out whether or not they're likely to make it (at the sign when it starts flashing?--you're good; still a good dozen meters away?--you're out), whereas a flashing green orb basically tempts drivers to run the light, because you're not sure how quickly you're going to reach the light (so speed up or prepare to stop).

My problem with the "prepare to stop when flashing" signs is that some of them just say "prepare to stop" and flash all the time.  So, when I see a sign like that, I'm never sure if I should even trust it or not.  There have been several times that I started to slow down at one of those signs, only to realize as I crossed the intersection at 10 mph under the limit (on a green light, with annoyed traffic passing me by) that there was no need to slow down at all because the lights always flash.  At least when the indication is part of the stoplight itself, you know darned well the light is about to change.

I don't think I've heard of that before. I know of two "signal ahead" signs that flash perpetually in my area (here and here), but they don't indicate to drivers that they are supposed to stop when they see the lights flashing (otherwise, drivers would forever be slowing for a light that isn't always changing). I do find these lights extremely annoying.

What I like are the signs that flash only when the lights are about to turn red, and when they're red. They're not strictly necessary on low-speed roads, but on high speed roads (such as the one I linked to in the first reply, or this one), they are extremely helpful. No surprising heavy braking.

MoDOT eliminates any ambiguity by having their signs read "SIGNAL AHEAD", with a black panel at the top of the sign with red LEDs forming the word "RED" that flashes, thus forming the full legend "RED SIGNAL AHEAD". When the signal is green, of course, the word "RED" remains dark.

Does the sign flash RED in advance of the signal turning red, or just when it's red? I'd appreciate a bit of a warning if on a high-speed road.

[kj3400]

{b} 4-second flashing green, followed by 4-second yellow

{b} is a good middle-ground, but you'd still have people who will begin to slow when they see the flashing green. I'd also rather reserve the flashing green for pedestrian crossings (BC's adaptation), regardless if flashing green is allowed in the States.

A better idea, and something I see all the time in BC, is advanced "prepare to stop when flashing" signs. This is basically an MUTCD-compliant variation of {b}, but probably safer because it tells traffic from a ways out whether or not they're likely to make it (at the sign when it starts flashing?--you're good; still a good dozen meters away?--you're out), whereas a flashing green orb basically tempts drivers to run the light, because you're not sure how quickly you're going to reach the light (so speed up or prepare to stop).

My problem with the "prepare to stop when flashing" signs is that some of them just say "prepare to stop" and flash all the time.  So, when I see a sign like that, I'm never sure if I should even trust it or not.  There have been several times that I started to slow down at one of those signs, only to realize as I crossed the intersection at 10 mph under the limit (on a green light, with annoyed traffic passing me by) that there was no need to slow down at all because the lights always flash.  At least when the indication is part of the stoplight itself, you know darned well the light is about to change.

I don't think I've heard of that before. I know of two "signal ahead" signs that flash perpetually in my area (here and here), but they don't indicate to drivers that they are supposed to stop when they see the lights flashing (otherwise, drivers would forever be slowing for a light that isn't always changing). I do find these lights extremely annoying.

What I like are the signs that flash only when the lights are about to turn red, and when they're red. They're not strictly necessary on low-speed roads, but on high speed roads (such as the one I linked to in the first reply, or this one), they are extremely helpful. No surprising heavy braking.

MoDOT eliminates any ambiguity by having their signs read "SIGNAL AHEAD", with a black panel at the top of the sign with red LEDs forming the word "RED" that flashes, thus forming the full legend "RED SIGNAL AHEAD". When the signal is green, of course, the word "RED" remains dark.

Does the sign flash RED in advance of the signal turning red, or just when it's red? I'd appreciate a bit of a warning if on a high-speed road.

The two I know of in Maryland start flashing at the point where the light will turn red when you reach it.

[Scott5114]

{b} 4-second flashing green, followed by 4-second yellow

{b} is a good middle-ground, but you'd still have people who will begin to slow when they see the flashing green. I'd also rather reserve the flashing green for pedestrian crossings (BC's adaptation), regardless if flashing green is allowed in the States.

A better idea, and something I see all the time in BC, is advanced "prepare to stop when flashing" signs. This is basically an MUTCD-compliant variation of {b}, but probably safer because it tells traffic from a ways out whether or not they're likely to make it (at the sign when it starts flashing?--you're good; still a good dozen meters away?--you're out), whereas a flashing green orb basically tempts drivers to run the light, because you're not sure how quickly you're going to reach the light (so speed up or prepare to stop).

My problem with the "prepare to stop when flashing" signs is that some of them just say "prepare to stop" and flash all the time.  So, when I see a sign like that, I'm never sure if I should even trust it or not.  There have been several times that I started to slow down at one of those signs, only to realize as I crossed the intersection at 10 mph under the limit (on a green light, with annoyed traffic passing me by) that there was no need to slow down at all because the lights always flash.  At least when the indication is part of the stoplight itself, you know darned well the light is about to change.

I don't think I've heard of that before. I know of two "signal ahead" signs that flash perpetually in my area (here and here), but they don't indicate to drivers that they are supposed to stop when they see the lights flashing (otherwise, drivers would forever be slowing for a light that isn't always changing). I do find these lights extremely annoying.

What I like are the signs that flash only when the lights are about to turn red, and when they're red. They're not strictly necessary on low-speed roads, but on high speed roads (such as the one I linked to in the first reply, or this one), they are extremely helpful. No surprising heavy braking.

MoDOT eliminates any ambiguity by having their signs read "SIGNAL AHEAD", with a black panel at the top of the sign with red LEDs forming the word "RED" that flashes, thus forming the full legend "RED SIGNAL AHEAD". When the signal is green, of course, the word "RED" remains dark.

Does the sign flash RED in advance of the signal turning red, or just when it's red? I'd appreciate a bit of a warning if on a high-speed road.

In advance. You can see the sign start to flash, then see the light turn yellow a few seconds after. MoDOT gets a lot of shit for being perpetually broke, but they usually do a good job with what they have, in my opinion.

I found a picture in my archives.