Under-SPUIs: Traffic signals before left/right turns gore split

[SkyPesos]

I'm currently in the St Louis area, which has no shortage of SPUI interchanges that go under the freeway. A common problem I have when making left turns from the off-ramp is the visibility of the traffic signals. I don't see my first left turn signal until after the gore split from the right turn lane(s) and the curve (signal at Point A on the quick diagram I drew below for reference). When the cars waiting for the left turn isn't long enough (which is pretty common here), I can't tell if it's a red or green light until past that curve.

A simple solution to this I thought of is placing extra supplemental signals before the split, either at the front of the gore (Point C on the diagram), or on the sides (Point D for left turns, E for right turns). Do any existing SPUI interchanges elsewhere already do one of my proposed signal layouts?

[paulthemapguy]

I have nothing more to say than that I agree with you. There needs to be a signal visible from farther than 50 feet for obvious safety reasons. I really struggle with this one in Grand Rapids. https://goo.gl/maps/5ziwmigMWBusc8hA7

[jeffandnicole]

I have nothing more to say than that I agree with you. There needs to be a signal visible from farther than 50 feet for obvious safety reasons. I really struggle with this one in Grand Rapids. https://goo.gl/maps/5ziwmigMWBusc8hA7

Just to point out...that point is about 300' away from the signal.  The ramp has a signed 30 mph advisory speed. While the signals, especially the ground mounted one on the right, could be positioned a little better, no one needs a signal at this point on a ramp. 

As for the OP, signals are expected to be at or beyond the stop line.  Posting a signal at a gore point invites confusion as some motorists may believe that is the point where they would need to stop.  A signal that far ahead of the stop line could also be green at the time the motorist is passing near it, and by the time the motorist gets to the stop line, the light could be red. 

Using paul's example where the gore point is 300 feet from the stop line, a motorist driving at or slightly over the advisory speed of 30 mph would take 6 seconds to get from that gore point to the actual light; much longer than the normal time it would take a light to turn from green to yellow to red on a 30 mph roadway. 

[jakeroot]

One solution employed by WSDOT in Olympia, Washington (both left and right turns are signalized). Basically, have a full-blown signal mast-arm in the gore area, with signals mounted on the mast arms. Not one of these signals are visible directly at the stop line, but they are very visible coming down the off-ramp. At the stop line, the only visible signals are two mounted almost directly next to each other hanging from the overpass.

The other solution, which is more typical, is to just mounted a single post-mounted signal near the stop line and pray drivers see it.

British Columbia employs left and right side signals, but visible only as you near the stop line.



One option to consider would be how Arizona treat its SPUIs where there are through movements. The overhead far-side mast arms basically act as a supplemental signal. That GSV link shows a large vehicle, and yet at least a few signals are still visible. Granted, most of what you can see are through signals (in this specific case), but for a regular SPUI, this display could be adapted.

[wanderer2575]

I have nothing more to say than that I agree with you. There needs to be a signal visible from farther than 50 feet for obvious safety reasons. I really struggle with this one in Grand Rapids. https://goo.gl/maps/5ziwmigMWBusc8hA7

There's a supplemental side-mounted signal at the stop line, which usually would help as its being farther to the right means it is visible sooner but without causing any confusion about the proper stop point.  That seems to be standard at all SPUIs I have seen in Michigan, whether the junction point is below or above the freeway.  However, this Grand Rapids case has a pedestrian crossing sign posted right in front of the signal, blocking it from view, and the signal is pointed too far to the right.

[jakeroot]

I have nothing more to say than that I agree with you. There needs to be a signal visible from farther than 50 feet for obvious safety reasons. I really struggle with this one in Grand Rapids. https://goo.gl/maps/5ziwmigMWBusc8hA7

There's a supplemental side-mounted signal at the stop line, which usually would help as its being farther to the right means it is visible sooner but without causing any confusion about the proper stop point.  That seems to be standard at all SPUIs I have seen in Michigan, whether the junction point is below or above the freeway.  However, this Grand Rapids case has a pedestrian crossing sign posted right in front of the signal, blocking it from view, and the signal is pointed too far to the right.

The signal appears to have been moved by someone (or something) causing it to point too far to the right. Old GSV imagery shows that it was formerly pointed [correctly] at traffic proceeding down the off-ramp.

[jakeroot]

Australia doesn't have much of a solution either, from the looks of it:

This SPUI in Brisbane has protected turns in both directions, and has dual left and right turn signals on both ends of each stop line. This particular SPUI is quite compact, and the left and right turn signals in the middle porkchop island are quite close to each other, kind of like the OP's diagram.

This SPUI in Sydney is larger, more akin to American SPUIs. It also has dual left and right turn signals on both ends of each stop line, but the larger porkchop island means the right turn signals are quite a ways off to the right. Large trucks in the left right-turn lane may block the only visible signal, as can be the case in the US as well (though, 'right left-turn lane' of course).

Outside of Australia, looking at this SPUI in Singapore, also not much of a solution besides the signal placement on both edges of the stop line, same as Australia.

One potential solution, which I could diagram if I found the time, would be to pull the stop line back far enough for a supplemental traffic signal on the left edge of a stop line to be visible to traffic coming down the off-ramp. Most SPUIs have the stop line close to the intersection, and only supplemental traffic signals on the right edge of a stop line are visibly. If there even is one, of course.

[sprjus4]

I like the way Chesapeake, VA implemented them along US-17 Dominion Blvd at the VA-165 interchange. They are actually mounted up on the bridge, so you can see the color of the signal from afar.

https://maps.app.goo.gl/kwb7sX8DtRrbgtco8?g_st=ic

Not so much for this second one, which is for northbound (the less busier ramp), but either way in both cases, it's also ground mounted with full visibility.

https://maps.app.goo.gl/3Wd8dpWJp8JQwq198?g_st=ic

[jakeroot]

I like the way Chesapeake, VA implemented them along US-17 Dominion Blvd at the VA-165 interchange. They are actually mounted up on the bridge, so you can see the color of the signal from afar.

https://maps.app.goo.gl/kwb7sX8DtRrbgtco8?g_st=ic

Not so much for this second one, which is for northbound (the less busier ramp), but either way in both cases, it's also ground mounted with full visibility.

https://maps.app.goo.gl/3Wd8dpWJp8JQwq198?g_st=ic

I think attaching a signal or signals to an overpass is actually quite common for SPUI-under-freeway interchanges. The issue is just the retaining wall for the overpass, or the curves, typically mean that the signals are not visible until you are nearly around the bend and at the stop line. Hence the propensity to use supplemental signals in the porkchop island.

These examples from Virginia are interesting though, because it's true that those overhead signals are usually not visible until the last second. Only reason this seems to be the case is because the retaining wall for the overpass is so far off to the left. Typical SPUIs (at least those I'm used to) often have a slope, or retaining wall that is closer to the off-ramp than the overpass, making it impossible to see the overhead signals until you're nearly at the stop line.

[Revive 755]

A simple solution to this I thought of is placing extra supplemental signals before the split, either at the front of the gore (Point C on the diagram), or on the sides (Point D for left turns, E for right turns). Do any existing SPUI interchanges elsewhere already do one of my proposed signal layouts?

Technically many of the signals for the left turns probably would not comply with the 2009 MUTCD:

If supplemental post-mounted signal faces are used, the following limitations shall apply:
A. Left-turn arrows and U-turn arrows to the left shall not be used in near-right signal faces.
B. Right-turn arrows and U-turn arrows to the right shall not be used in far-left signal faces. A far-side median-mounted signal face shall be considered a far-left signal for this application.

The draft text for the next MUTCD (at least back around the comment period in 2021) would have allowed this setup IIRC.

Using an advanced flashing 'prepare to stop' assembly may be a better option if the ramp is long enough.

[jakeroot]

A simple solution to this I thought of is placing extra supplemental signals before the split, either at the front of the gore (Point C on the diagram), or on the sides (Point D for left turns, E for right turns). Do any existing SPUI interchanges elsewhere already do one of my proposed signal layouts?

Technically many of the signals for the left turns probably would not comply with the 2009 MUTCD:

If supplemental post-mounted signal faces are used, the following limitations shall apply:
A. Left-turn arrows and U-turn arrows to the left shall not be used in near-right signal faces.
B. Right-turn arrows and U-turn arrows to the right shall not be used in far-left signal faces. A far-side median-mounted signal face shall be considered a far-left signal for this application.

The draft text for the next MUTCD (at least back around the comment period in 2021) would have allowed this setup IIRC.

Using an advanced flashing 'prepare to stop' assembly may be a better option if the ramp is long enough.

I would have certainly thought there would be an exception if this were the only permitted movement for an approach; is there not?

I think of situations like DDIs, where the off-ramps can often be signalized as right and left turns; much like a SPUI, there is usually a near-right (left turn) or near-left (right turn) signal face due to the angle of the curve associated with the turn.

If there really is no exception, the way to get around this is quite easy: just don't use arrow signals.

[SkyPesos]

One solution employed by WSDOT in Olympia, Washington (both left and right turns are signalized). Basically, have a full-blown signal mast-arm in the gore area, with signals mounted on the mast arms. Not one of these signals are visible directly at the stop line, but they are very visible coming down the off-ramp. At the stop line, the only visible signals are two mounted almost directly next to each other hanging from the overpass.

I like this one. Increases visibility like what I want, but not placed too far from the stop line.

The other solution, which is more typical, is to just mounted a single post-mounted signal near the stop line and pray drivers see it.

This is the issue I have with every single SPUI that goes under the highway in my area. None of them are compact enough or have left turn lanes that don't angle too far to the left (like some of the examples you and others posted in this thread) that you can see from further away.

Of the ones in the St Louis area I use frequently
-I-170 to MO 340: GSV shows it like it's fine, but from the leftmost lane at the height of an average sedan and with the wall on the left, I don't see the near-side post mounted signal until after the split, and overhead ones (the St Louis area like to do horizontal signals under the overpass for under-freeway SPUIs) a bit after that
- MO 141 to MO 100: Similar issues as above
- US 40 to US 61/67: A bit worse due to the greater curvature of the left turn, also there's no overhead signals (just a near post-mounted and a far post-mounted under the bridge)
- I-170 to MO 180: I have the most visibility issues with this one, and also probably the most difficult to fix of these three, as the I-170 median is very wide here, with the signal in the open air below the median. I normally drive up to SPUIs expecting a red light, but way too many times where it was a green turning yellow here.

[jeffandnicole]

A simple solution to this I thought of is placing extra supplemental signals before the split, either at the front of the gore (Point C on the diagram), or on the sides (Point D for left turns, E for right turns). Do any existing SPUI interchanges elsewhere already do one of my proposed signal layouts?

Technically many of the signals for the left turns probably would not comply with the 2009 MUTCD:

If supplemental post-mounted signal faces are used, the following limitations shall apply:
A. Left-turn arrows and U-turn arrows to the left shall not be used in near-right signal faces.
B. Right-turn arrows and U-turn arrows to the right shall not be used in far-left signal faces. A far-side median-mounted signal face shall be considered a far-left signal for this application.

This language, and this section if the MUTCD, would apply to a roadway where there are multiple movements in a continous width across the roadway. . A porkchop or center median eliminates the condition referenced and results in its own roadway, where all lanes have the same movement. Section 4D.05, Support Paragraph 6 permits the replacement of a circular green with a green arrow in these instances.

06 If not otherwise prohibited, steady red, yellow, and green turn arrow signal indications may be used instead of steady circular red, yellow, and green signal indications in a signal face on an approach where all traffic is required to turn or where the straight-through movement is not physically possible.

[Revive 755]

^ To me it's debatable due to the "not otherwise prohibited" language.  Then there's the language very similar to  4D.13 Paragraph 10 in 4D.05 Paragraph 08.

[jakeroot]

There are a lot of agencies that violate that rule if your interpretation is correct. Virtually all DDIs have near-right left-facing green arrows for the off-ramp left turns, as near-right is the most logical placement for a left curve. Same for SPUIs.

[plain]

The signaling at the lone SPUI on the Virginia Peninsula is probably the worst one I've seen yet. Not only are the left turn ones not visible until halfway around the curve, they're all ground mounted and they're fucking PVs to boot 

https://maps.app.goo.gl/3ipqmx4EjEQVKaXc6

[ran4sh]

A simple solution to this I thought of is placing extra supplemental signals before the split, either at the front of the gore (Point C on the diagram), or on the sides (Point D for left turns, E for right turns). Do any existing SPUI interchanges elsewhere already do one of my proposed signal layouts?

Technically many of the signals for the left turns probably would not comply with the 2009 MUTCD:

If supplemental post-mounted signal faces are used, the following limitations shall apply:
A. Left-turn arrows and U-turn arrows to the left shall not be used in near-right signal faces.
B. Right-turn arrows and U-turn arrows to the right shall not be used in far-left signal faces. A far-side median-mounted signal face shall be considered a far-left signal for this application.

The draft text for the next MUTCD (at least back around the comment period in 2021) would have allowed this setup IIRC.

Using an advanced flashing 'prepare to stop' assembly may be a better option if the ramp is long enough.

Nothing in the diagram is a far-left signal face, and none of the near right faces have left turn arrows...

[sprjus4]

The signaling at the lone SPUI on the Virginia Peninsula is probably the worst one I've seen yet. Not only are the left turn ones not visible until halfway around the curve, they're all ground mounted and they're fucking PVs to boot 

https://maps.app.goo.gl/3ipqmx4EjEQVKaXc6

Not quite the lone SPUI for the Peninsula... not that it's any better though: https://maps.app.goo.gl/qwVSX1WFTCLA3epV8?g_st=ic

[Henry]

By a long shot, I prefer SPUI's over the freeway, but if they have to go under, I'd like for the signals to be overhead and attached to the bridge at an angle.

[Revive 755]

Nothing in the diagram is a far-left signal face, and none of the near right faces have left turn arrows...

If this is referring to the diagram at the start of this thread, the signals for the left turn at A and C fall into the 'near right' category, and they are drawin with red left arrows.

[ran4sh]

There isn't a straight movement so it could be argued that they shouldn't be counted as being on the right. Of course, some DOT would have to request an interpretation to make it official