Left turn signal mounted differently on mast?

[SeriesE]

Is there a reason why sometimes the left turn signal is mounted differently than through signals?

https://www.google.com/maps/@34.140079,-118.0314099,3a,82.5y,356.81h,91.24t/data=!3m6!1e1!3m4!1sdFTY32xlDXHDgcd_1qUKbA!2e0!7i16384!8i8192

https://www.google.com/maps/@37.6891726,-120.994375,3a,89.7y,37.68h,89.84t/data=!3m6!1e1!3m4!1suAtccTiVmNguKyWpiIWwsQ!2e0!7i16384!8i8192

In this case, the mount for left turn signal is on the top; the mount for the through signal is between the red and the yellow lights.

[JoePCool14]

The only thing I can think of in this case is that they want the left turn signal placed lower than the main signal. I can't think of why they'd want that though. It looks tacky.

[jakeroot]

This is extremely common on the west coast. Mostly California but there are installations of the like in WA and OR too. Probably NV and AZ as well.

As to the reason: it remains a mystery to me. Drivers seem unlikely to interpret the different mounting heights in a meaningful way, so it must be related to something technical. But since it is far from the norm even in California, despite nearly identical signal standards throughout the state (with the left turn signal mounting height being one of the most notable inconsistencies), there's really no clear indication from installations alone what that technical reason is.

If there are any California (or west coast) engineers, speak up now!

[US 89]

I always assumed the lights were all supposed to be the same height, and the different mount locations were supposed to balance out the left side of the mast-arm being higher than the right.

Alternatively, it could just be to emphasize the left turn signal in some way? There's at least one light in Orinda that takes this kind of thing to an extreme. At least that one is clearly intentional, as opposed to the other examples which just look sloppy and careless.

[jakeroot]

I always assumed the lights were all supposed to be the same height, and the different mount locations were supposed to balance out the left side of the mast-arm being higher than the right.

Alternatively, it could just be to emphasize the left turn signal in some way? There's at least one light in Orinda that takes this kind of thing to an extreme. At least that one is clearly intentional, as opposed to the other examples which just look sloppy and careless.

I've never heard of any rule about signals being the same height. They are typically centered against the mast arm. Even in California, this is the norm. In other states with straight mast arms, they are still centered; at this example in Sparks, NV, you can see the signals gently sloping upwards. This is the norm in most states that use mast arms. The only exception I can think of is Oregon, who likes to align the signals with each other. I think this looks weird, personally, with a very off-balance appearance.

The 'emphasis' suggestion is usually the main argument, but as I mentioned in my post, it seems remarkably unlikely since drivers would be unlikely to extract any meaning from signal positioning on the mast arm. The Orinda example is certainly extreme and may be a case of intentional emphasis (it may have been a red circle at one point), but this doesn't seem likely with the left turn signal example in the OP. After all, the plumbizer being inserted above the red instead of below it (guessing on the technical terminology here -- no need to correct me) is just not obvious to anyone except those who are looking for it (aka, roadgeeks). I also wouldn't call the OP's example sloppy or careless, unless you are saying that it's a sloppy/careless attempt to differentiate the left turn signal; I would actually agree with that.

[Brandon]

When I first saw this thread, I thought you were talking about signals like they have in Nebraska, like these:
https://goo.gl/maps/BpU1QfqK4nuswP7E9

[JoePCool14]

I always assumed the lights were all supposed to be the same height, and the different mount locations were supposed to balance out the left side of the mast-arm being higher than the right.

Alternatively, it could just be to emphasize the left turn signal in some way? There's at least one light in Orinda that takes this kind of thing to an extreme. At least that one is clearly intentional, as opposed to the other examples which just look sloppy and careless.

I've seen this type on here before, and always thought that looked really strange. There has to be some reason why they chose to do that. If there is, I just can't see it.

Illinois tends to line up the lights on mast arms, though the variation usually comes from the 5-light towers since we do not use doghouses here except for one specific location. Also, many of our newer, larger installations keep the mast arm more horizontal.

Example 1: https://goo.gl/maps/cKhGSZd32C3ftmZX9
Example 2: https://goo.gl/maps/fg6nUeYUWs9pfCFT9

[paulthemapguy]

I wouldn't overthink it; I think the only reason they hang the signal head at the end of the mast from its very top is to prevent it from slanting later on in the signal's life.  If the attachment point of the signal head is somewhere in the middle, there's a greater chance of the signal head tilting due to wind loads, without self-correction.  Winds will blow the signal head around as it hangs from its top as well, but the self-weight of the signal head pulling straight down from the mast arm will make it more likely to retain more of its vertical axis.  Imagine if they did the opposite of this, and attached the signal head to the mast arm at the very bottom- the signal head would swing and flop all over the place!

[jakeroot]

I wouldn't overthink it; I think the only reason they hang the signal head at the end of the mast from its very top is to prevent it from slanting later on in the signal's life.  If the attachment point of the signal head is somewhere in the middle, there's a greater chance of the signal head tilting due to wind loads, without self-correction.  Winds will blow the signal head around as it hangs from its top as well, but the self-weight of the signal head pulling straight down from the mast arm will make it more likely to retain more of its vertical axis.  Imagine if they did the opposite of this, and attached the signal head to the mast arm at the very bottom- the signal head would swing and flop all over the place!

Wind-loading concerns wouldn't be a first for California .

That seems like a relatively plausible theory, but then I would think it would be more common then. Even as it stands, it's not like every far-left mast arm signal in California is mounted from the top. Many new installations do not feature this installation style (the overall trend seems to have died down from peaking perhaps around 20 or 30 years ago).

[US 89]

I've never heard of any rule about signals being the same height. They are typically centered against the mast arm. Even in California, this is the norm. In other states with straight mast arms, they are still centered; at this example in Sparks, NV, you can see the signals gently sloping upwards. This is the norm in most states that use mast arms. The only exception I can think of is Oregon, who likes to align the signals with each other. I think this looks weird, personally, with a very off-balance appearance.

Out of curiosity, I hunted down Utah's signalized intersection design manual. It does specify that the bottom of all signal heads should be level with each other, and that all should be mounted such that at least half of the signal is below the mast-arm to avoid wind issues:

The signal head closest to the highest point of the roadway surface must have a minimum of 18.5-foot and maximum 21-foot clearance from bottom of signal head assembly and the roadway surface. If an 18.5-foot clearance is not attainable, a 17.5-foot minimum is allowed by written approval from the Region Traffic Operations Engineer. Level the remaining signal heads to the same bottom elevation. Mount the signal assembly such that half or more of the signal head assembly is below the mast arm. Signal heads mounted too far above the mast arm tend to get twisted by the wind. If the signal is on a high load route contact the Region Traffic Operations Engineer for clearances.

So that's what I'm used to. Should be noted that Utah uses brackets to mount all its traffic lights, which probably makes it a bit easier to play around with the exact height.

[roadfro]

I've also always kinda been curious about this as well. It does seem to be quite prevalent in areas of California, especially in slightly-older installations using curved mast arms (such as the OP's two examples). At one point, I thought maybe there was just a shipment of left turn signals where the plumbizer or other attachment was already affixed to the top, but the mounting phenomenon is prevalent across too many California jurisdictions to be random or coincidental. I also just kinda assumed it was a way to emphasize the left turn signal, but jakeroot makes the good point that there's usually other context that makes the signal perfectly clear (it's also incredibly common in California for the overhead left turn signal face to have some kind of left turn-related sign or a No U-Turn sign adjacent that further drives the point across).


This is not something you commonly see in Nevada, although there are a few examples here in Reno-Sparks that I know of:

• Ryland Ave WB at Wells Ave in Reno.
• N McCarran Blvd NB at Victorian Ave/I-80 EB off ramp in Sparks. Looks really odd on the curved mast arm with one through signal on the lower part of the curve.
• N McCarran Blvd EB/SB at Baring Blvd in Sparks. An odd example of two left turn signal heads and only the end one mounted in the California style of the OP. (Also a rare example of only one overhead through signal for a 2+ lane road outside of downtown.)
• Baring Blvd WB at Sparks Blvd in Sparks. A different example with the left turn signal's plumbizer mounted between yellow and green indications.

There's also a few examples locally where the left turn signal head is mounted at the normal height, but the through signal heads are mounted abnormally (with the plumbizer between yellow and green, instead of yellow and red) for no apparent reason:

• N McCarran Blvd EB at Sullivan Ln in Sparks.
• Vista Blvd SB at Prater Way in Sparks.
• S Virginia St NB&SB at Longley Ln/Huffaker Ln in Reno.
• S Carson St (US 395 Bus) NB at Koontz Ln in Carson City (although this one may have been removed due to construction).

[wanderer2575]

I think it's simply about keeping all the signals at the same height for easier viewing.  It's the same as vertical extensions on fixtures hanging from span wires; I can't think of any other reason for those (for example:  https://goo.gl/maps/yexLKzkQxebRju1J7).

And it isn't limited to only left-turn signals, for example:  https://goo.gl/maps/5N7XgtRLNCpLVX546

[roadfro]

Alternatively, it could just be to emphasize the left turn signal in some way? There's at least one light in Orinda that takes this kind of thing to an extreme. At least that one is clearly intentional, as opposed to the other examples which just look sloppy and careless.

There's a few other jurisdictions in northern California where this weird end curve is used to mount a left turn signal at a lower than normal height. I find this incredibly peculiar.

I may come back and put in some examples when I get a minute. But I will say that this one is more unusual that the other examples I recall seeing at least had a small raised median for the signal to hang over. This one doesn't, and seems like it would be incredibly susceptible to getting struck by taller vehicles.

[roadfro]

I think it's simply about keeping all the signals at the same height for easier viewing.  It's the same as vertical extensions on fixtures hanging from span wires; I can't think of any other reason for those (for example:  https://goo.gl/maps/yexLKzkQxebRju1J7).

But a lot of times, as evidenced with many examples linked in the thread, places the left turn signal head at a noticeably different height than the adjacent through signal heads.

[SeriesE]

When I first saw this thread, I thought you were talking about signals like they have in Nebraska, like these:
https://goo.gl/maps/BpU1QfqK4nuswP7E9

Is this supposed to be Nebraska's version of the doghouse signal?

[wanderer2575]

I think it's simply about keeping all the signals at the same height for easier viewing.  It's the same as vertical extensions on fixtures hanging from span wires; I can't think of any other reason for those (for example:  https://goo.gl/maps/yexLKzkQxebRju1J7).

But a lot of times, as evidenced with many examples linked in the thread, places the left turn signal head at a noticeably different height than the adjacent through signal heads.

Quite so.  I was responding to the OP's example, which seems to be only for purposes of keeping the fixtures at the same height.

As for deliberate height variances, I think US 89's theory of emphasizing that signal is for a different traffic movement is most plausible.

[SeriesE]

I always assumed the lights were all supposed to be the same height, and the different mount locations were supposed to balance out the left side of the mast-arm being higher than the right.

Alternatively, it could just be to emphasize the left turn signal in some way? There's at least one light in Orinda that takes this kind of thing to an extreme. At least that one is clearly intentional, as opposed to the other examples which just look sloppy and careless.

Orinda one looks like it's to avoid the overhead lines blocking the signal, but I do see that kind of mast arm in other places even when there's no visual obstructions like this.

[SkyPesos]

When I first saw this thread, I thought you were talking about signals like they have in Nebraska, like these:
https://goo.gl/maps/BpU1QfqK4nuswP7E9

Is this supposed to be Nebraska's version of the doghouse signal?

I see some doghouse variants omit the dedicated yellow arrow bulb, and uses the same bulb as the green arrow for the yellow one, so it looks like a sideways "L" shape. They're mostly in other countries, like I see them in the UK and Japan a lot.

[jakeroot]

I've never heard of any rule about signals being the same height. They are typically centered against the mast arm. Even in California, this is the norm. In other states with straight mast arms, they are still centered; at this example in Sparks, NV, you can see the signals gently sloping upwards. This is the norm in most states that use mast arms. The only exception I can think of is Oregon, who likes to align the signals with each other. I think this looks weird, personally, with a very off-balance appearance.

Out of curiosity, I hunted down Utah's signalized intersection design manual. It does specify that the bottom of all signal heads should be level with each other, and that all should be mounted such that at least half of the signal is below the mast-arm to avoid wind issues:

The signal head closest to the highest point of the roadway surface must have a minimum of 18.5-foot and maximum 21-foot clearance from bottom of signal head assembly and the roadway surface. If an 18.5-foot clearance is not attainable, a 17.5-foot minimum is allowed by written approval from the Region Traffic Operations Engineer. Level the remaining signal heads to the same bottom elevation. Mount the signal assembly such that half or more of the signal head assembly is below the mast arm. Signal heads mounted too far above the mast arm tend to get twisted by the wind. If the signal is on a high load route contact the Region Traffic Operations Engineer for clearances.

So that's what I'm used to. Should be noted that Utah uses brackets to mount all its traffic lights, which probably makes it a bit easier to play around with the exact height.

Cheers for finding that. I did some research for WA; this is their manual and it does not mention anything about signal levelling. Looking briefly at other states, I don't think any others have this levelling rule.

I actually did some zooming around Utah on Street View and was actually surprised to see how much signal levelling was occurring. It reminds me a bit of Oregon. Not sure I noticed this before, but then I know a lot of Utah has totally-level mast arms where it wouldn't be totally obvious.

That said, it seems odd to me that Utah would request signals be installed level with each other while also simultaneously requiring at least half of the signal to be mounted below the mast arm. The only realistic way to achieve this is to mount all of the signals on a totally-horizontal mast arm, where it seems they would be level with each other anyway. It surprises me that Utah would so often (aka: not all the time--I know straight mast arms are still common) specify the California-style curved mast arm but then basically rule-out installing anything on the curved bit, least without it being mounted very awkwardly (good example in downtown SLC; another nearby example that doesn't follow the rule but I personally view as superior).

[jakeroot]

When I first saw this thread, I thought you were talking about signals like they have in Nebraska, like these:
https://goo.gl/maps/BpU1QfqK4nuswP7E9

Is this supposed to be Nebraska's version of the doghouse signal?

Those are side-by-side doghouses. They are the norm in many places, including Colorado, West Virginia, and New York City.

I think it's simply about keeping all the signals at the same height for easier viewing.  It's the same as vertical extensions on fixtures hanging from span wires; I can't think of any other reason for those (for example:  https://goo.gl/maps/yexLKzkQxebRju1J7).

But a lot of times, as evidenced with many examples linked in the thread, places the left turn signal head at a noticeably different height than the adjacent through signal heads.

Quite so.  I was responding to the OP's example, which seems to be only for purposes of keeping the fixtures at the same height.

As for deliberate height variances, I think US 89's theory of emphasizing that signal is for a different traffic movement is most plausible.

Even in the OP's example, we see a left turn signal that is noticeably lower than the through signal. Your suggestion, then, doesn't seem plausible, particularly as California has no rule for signal levelling.

The deliberate height variance to more clearly indicate the signal being for a different maneuver may be the most plausible reason at this point, but as indicated by myself and roadfro above, there are at least a couple of reasons why this makes little sense.

[roadfro]

Alternatively, it could just be to emphasize the left turn signal in some way? There's at least one light in Orinda that takes this kind of thing to an extreme. At least that one is clearly intentional, as opposed to the other examples which just look sloppy and careless.

There's a few other jurisdictions in northern California where this weird end curve is used to mount a left turn signal at a lower than normal height. I find this incredibly peculiar.

I may come back and put in some examples when I get a minute. But I will say that this one is more unusual that the other examples I recall seeing at least had a small raised median for the signal to hang over. This one doesn't, and seems like it would be incredibly susceptible to getting struck by taller vehicles.

Examples:

• Reservation Rd (CR G17) at shopping center, Marina, CA
  
• Watt Ave at Fair Oaks Blvd, Sacramento, CA
  
• Fair Oaks Blvd at Eastern Ave, Sacramento, CA
  

I've mentioned in another thread that many of these seem to have had the curved part of the mast arm holding the left turn signal added on after the fact, and were often in places where there's a narrow median. The two Sacramento examples I found fit this.

I previously opined that these potentially replaced a post-mounted left turn signal in the median, and this treatment was used to achieve a similar median-post-mounted signal height. Don't know if that's true, but it does support the explanation that the left turn signal mounted differently on purpose to be noticeable.

[mrsman]

You posed a very interesting question.

I have a theory, but I have no evidence to support it.

When CA first put in place protected left turn signals, they usually came in two main varieties: R-Y-GA where the R and Y were 8" heads and the GA was 12" head (and the red and yellow signals were frequently louvered), or R-Y-GA with all 12" heads, but those heads were all 3M style programmable visibility (PV) signal heads.  Since a red arrow was not used, there was a good sense that they needed to distinguish the signals from the thru signals in some sense for safety reasons.  Ideally, the left turn signals should only be visible to those in the left turn lane.  This is where the louvering and the use of the PV signals comes in.  In my mind it seems that a lower signal face would be directly showing for the driver who is in the left turn lane, and ideally only visible to those in the left turn lane.  The other signals are mounted higher, in order for traffic in the main lanes who are further back should be able to see the signal.

The later revisions of MUTCD require the left turn signal to be RA-YA-GA.  So many of these R-Y-GA signals were replaced with RA-YA-GA, but the signal mounts on the signs have not changed.

[Occidental Tourist]

That one is Marina looks like it's just waiting for a high profile vehicle to attempt an illegal u-turn at that intersection in order to be replaced.

[jakeroot]

You posed a very interesting question.

I have a theory, but I have no evidence to support it.

When CA first put in place protected left turn signals, they usually came in two main varieties: R-Y-GA where the R and Y were 8" heads and the GA was 12" head (and the red and yellow signals were frequently louvered), or R-Y-GA with all 12" heads, but those heads were all 3M style programmable visibility (PV) signal heads.  Since a red arrow was not used, there was a good sense that they needed to distinguish the signals from the thru signals in some sense for safety reasons.  Ideally, the left turn signals should only be visible to those in the left turn lane.  This is where the louvering and the use of the PV signals comes in.  In my mind it seems that a lower signal face would be directly showing for the driver who is in the left turn lane, and ideally only visible to those in the left turn lane.  The other signals are mounted higher, in order for traffic in the main lanes who are further back should be able to see the signal.

The later revisions of MUTCD require the left turn signal to be RA-YA-GA.  So many of these R-Y-GA signals were replaced with RA-YA-GA, but the signal mounts on the signs have not changed.

My only question, then, is why the trend continued even after the need to distinguish using alternative methods was made obsolete by all-arrow displays? As far as I know, California still installs the occasional left turn signal "hanging" from the end of the mast arm, as though hanging it slightly would still provide some benefit to signal distinguishing (my guess, as before: it doesn't).

[myosh_tino]

According to Caltrans' standard plans, the left-most signal on a mast arm is supposed to be a "hanging" one...





Like others have mentioned, the placement of the left-most signal varies widely across the state.  However, from what I've seen in and around where I live (near San Jose), the prevailing practice is to mount the left-most signal the same way the other signals are mounted.