Regional Boards > Mountain West
Protected Left Turns in Tucson AZ
ztonyg:
--- Quote from: roadiejay on April 17, 2018, 08:01:58 PM ---Does the new signal have 4 heads? I was just there recently... Speedway/Campbell, IIRC is protected only during peak hours, along with several other intersections along Speedway in the U of A corridor.
Non peak hours, the control is reverted to permissive/Protective (lag arrow) with a new FYA during the "Yield phase."
--- End quote ---
There is a 4 headed signal but underneath it there's a "left on green arrow only" sign which seems to mean that left turns wouldn't be permitted during a FYA "yield phase."
jakeroot:
I don't think this is related to the double left turn operation, especially since the approaches to Campbell Ave are single lane left turns. There are several single-lane protected lefts along Speedway that operate with TOD phasing, as can be seen in this Street View image: https://goo.gl/MGNdzr. The signs in the video are clearly unique in that "GREEN ARROW ONLY" signs are being used to restrict the movements to protected only, but it very well could be related to traffic levels. Or, in this case, a councillor who's getting involved where they shouldn't be. I would not be surprised if TDOT was forced to change the operation of this intersection by the councillor in question.
In particular, this sweeping generalisation really bothered me:
--- Quote from: Steve Kozachik, Tucson City Councillor (0:46 in YouTube Clip) ---[Protected lefts are] are recognised internationally as the single safest way to manage a major intersection
--- End quote ---
The notion that protected-only phasing is always safer is total bollocks. Protected-only left turns naturally have less capacity than permissive lefts, and as a result of that, often have larger delays. As delays increase, drivers grow impatient and start doing things that drivers who were patient wouldn't do, like push yellow lights or follow too closely. What I see in Seattle (at protected lefts) quite often is drivers who turn left after the yellow arrow is expired (since they don't want to wait for another cycle), and nearly clip a pedestrian who entered the crosswalk, not expecting a driver to so blatantly ignore a red signal. I can't seem to find the study at the moment (I will find it and I will post it here soon), but one near me concluded that permissive lefts eventually prove safer because traffic levels improved, which as far as they could tell, reduced driver frustration, leading them to perform less risky maneuvers. I guess allowing drivers the liberty to turn in a gap is less risky than not!
JKRhodes:
--- Quote from: ztonyg on April 18, 2018, 05:56:12 PM ---
--- Quote from: roadiejay on April 17, 2018, 08:01:58 PM ---Does the new signal have 4 heads? I was just there recently... Speedway/Campbell, IIRC is protected only during peak hours, along with several other intersections along Speedway in the U of A corridor.
Non peak hours, the control is reverted to permissive/Protective (lag arrow) with a new FYA during the "Yield phase."
--- End quote ---
There is a 4 headed signal but underneath it there's a "left on green arrow only" sign which seems to mean that left turns wouldn't be permitted during a FYA "yield phase."
--- End quote ---
They have a guy who changes out the signs twice a day... It's labor intensive, but it works great!
ztonyg:
--- Quote from: roadiejay on April 18, 2018, 11:09:58 PM ---
--- Quote from: ztonyg on April 18, 2018, 05:56:12 PM ---
--- Quote from: roadiejay on April 17, 2018, 08:01:58 PM ---Does the new signal have 4 heads? I was just there recently... Speedway/Campbell, IIRC is protected only during peak hours, along with several other intersections along Speedway in the U of A corridor.
Non peak hours, the control is reverted to permissive/Protective (lag arrow) with a new FYA during the "Yield phase."
--- End quote ---
There is a 4 headed signal but underneath it there's a "left on green arrow only" sign which seems to mean that left turns wouldn't be permitted during a FYA "yield phase."
--- End quote ---
They have a guy who changes out the signs twice a day... It's labor intensive, but it works great!
--- End quote ---
In all seriousness, I've seen this setup before where during periods of "protected only" operation the FYA never operates (only the green, yellow, and red arrows run during a cycle). During the "protected/permissive" operation, the FYA illuminates.
I'm interested to see how this operates with the sign. I can't imagine that anyone changes out the sign. So I'd guess that the FYA is switched off all the time and they run the 4 headed signal with only the green, yellow, and red arrow heads actually in operation.
jakeroot:
--- Quote from: ztonyg on April 19, 2018, 10:54:41 AM ---
--- Quote from: roadiejay on April 18, 2018, 11:09:58 PM ---
--- Quote from: ztonyg on April 18, 2018, 05:56:12 PM ---
--- Quote from: roadiejay on April 17, 2018, 08:01:58 PM ---Does the new signal have 4 heads? I was just there recently... Speedway/Campbell, IIRC is protected only during peak hours, along with several other intersections along Speedway in the U of A corridor.
Non peak hours, the control is reverted to permissive/Protective (lag arrow) with a new FYA during the "Yield phase."
--- End quote ---
There is a 4 headed signal but underneath it there's a "left on green arrow only" sign which seems to mean that left turns wouldn't be permitted during a FYA "yield phase."
--- End quote ---
They have a guy who changes out the signs twice a day... It's labor intensive, but it works great!
--- End quote ---
In all seriousness, I've seen this setup before where during periods of "protected only" operation the FYA never operates (only the green, yellow, and red arrows run during a cycle). During the "protected/permissive" operation, the FYA illuminates.
I'm interested to see how this operates with the sign. I can't imagine that anyone changes out the sign. So I'd guess that the FYA is switched off all the time and they run the 4 headed signal with only the green, yellow, and red arrow heads actually in operation.
--- End quote ---
To the best of my knowledge, Tucson has been slowly adopting the flashing yellow arrow city-wide. It looks as though this intersection was converted before being converted again to protected only.
The setup that you (ztonyg) describe is referred to as TOD phasing, aka Time of Day phasing. This is common in some areas near me. I'm personally not the biggest fan.
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