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PaperclipPerfector  12hr ago (text post)   470 thread views

Friday Fun Thread for April 10, 2026

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MUTCD sign R10-12, "left turn yield on green 🟢"

At least around here, it seems these are (slowly) getting replaced with a flashing yellow arrow, with an equivalent sign. A bit confusing at first, but I think it makes sense that it would use a typical "proceed with caution" indicator, not a "go".

That would be confusing to me; here a flashing green light indicates that a left turn is protected, so my interpretation of a flashing yellow arrow would probably be like protected but currently turning red so don't engage in a turn, I'd probably try, if I started turning already, to try and get out quickly rather than yield.

In the US, flashing green indications are not permitted (MUTCD § 4A.04 ¶ 01 item A).

The use of a flashing yellow arrow to indicate a permissive left turn was approved by the feds on an experimental basis in 2006 (Interim Approval 10) and on a permanent basis in 2009 (in the previous edition of the MUTCD). But adding an extra yellow arrow to a signal is a lot of money to spend, just to remind motorists of the default rule that they should be following anyway (on a green circle when neither a green arrow nor a "no left turn" sign is present).

This is a sensible signal but the implementation around me has been terrible. The left turn signal is a 3-stack of arrows, green, yellow, and red. The first part of the turn is a protected left, so it's a green arrow during this segment. Near the end of the protected left segment, it switches to solid yellow for 3 seconds. Now, my expectation would be that if the next period is unprotected turning, it would flash yellow, and it does, but not before turning solid red for 1 second. Every time I start proceeding on the yellow, expecting it to turn flashing, the solid red causes me to stomp the brakes in case I've made a mistake and the direction is changing. It's infuriating, and I wonder if anybody else has this terrible implementation in their area.

(My preference would be for it to transition immediately from green to flashing yellow - why do we need a warning that we're about to proceed with caution?)

Under MUTCD § 4F.01 ¶ 03:

my expectation would be that if the next period is unprotected turning, it would flash yellow, and it does, but not before turning solid red for 1 second

This is the default under item F.6.

My preference would be for it to transition immediately from green to flashing yellow

This is permitted (not recommended or required) under item F.6.b.

If you feel like making a long shot, you can try asking your jurisdiction about this signal, citing these specific passages of the MUTCD in your complaint.

Steady and flashing signal indications shall be applied as follows:

(F) A steady YELLOW ARROW signal indication:

(6) Shall be terminated by a RED ARROW signal indication for the same direction or a CIRCULAR RED signal indication except:

(b) When the movement controlled by the arrow is to continue on a permissive mode basis during an immediately following signal phase, the display of a CIRCULAR GREEN signal indication or flashing YELLOW ARROW signal indication shall be permitted following a steady YELLOW ARROW signal indication. To provide a red clearance interval, it shall be permitted to display a steady left-turn RED ARROW signal indication immediately following the steady left-turn YELLOW ARROW signal indication.

A friend of mine was in charge of signs and pavement markings for PennDOT District 6 before his retirement a few years ago. I once engaged him as an expert witness in a traffic case, just because I liked the idea of bringing in an expert to fight a speeding ticket. I'll have to ask him if there are any signs that annoy him, but he seems more irritated by poor implementation. A town near where he grew up made a bunch of traffic "improvements" that PennDOT thought were necessary but everyone else was against, and when the project was complete he drove down there to take a look and said that whatever other problems there were with the plan they got the signs wrong. He refuses to go into Pittsburgh because he doesn't like the way they do their signs.

In other sign-related news, there's an increasing problem, mostly in rural areas, of people, and especially large trucks, getting stuck on bad roads. This is the inevitable result of people blindly relying on GPS, not realizing that it will direct them onto anything open for vehicular traffic regardless of surface, winter maintenance status, etc. Some municipalities have responded by posting signs that say "No GPS Route" on roads where this is a particular problem. My friend told me that these were not MUTCD approved signs, and that they were posted on local roads (that don't strictly follow Federal guidelines) and not state roads, but that he thought that the MUTCD should adopt something similar, since one of the most frequent constituent complaints he received was trucks getting stuck on roads they had no business being on.

when the project was complete he drove down there to take a look and said that whatever other problems there were with the plan they got the signs wrong

LOL. Just a few weeks ago I myself sent to PennDOT a complaint about some signs that were blatantly wrong. Multiple signs all said "left lane ends, merge right", but in reality the right lane ended and motorists had to merge left! And I drove past these signs for many months before I got around to making the complaint. I imagine the lawsuit resulting from a crash at that location would be legendary. (No standards compliance? No design immunity!)

he thought that the MUTCD should adopt something similar

MUTCD-compliant signs serving this purpose already exist.

  • R3-1: "trucks over XX tons no right turn"

  • R5-2: "no trucks"

  • R12 series: "weight limit XX tons", "axle weight limit XX tons", "weight limit 2 axles XX T, 3 axles YY T, 4 axles ZZ T", etc.

  • W8 series: "pavement ends", "loose gravel", "rough road", etc.

Presumably the municipal governments are just too incompetent to install them (and pass ordinances backing up the R (regulatory) signs).

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