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Author Topic: Protected Left Turns in Tucson AZ  (Read 3492 times)

DJStephens

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Re: Protected Left Turns in Tucson AZ
« Reply #25 on: November 01, 2018, 10:22:30 PM »

What do you think of the indirect left turns or "Michigan lefts" planned or in use along Grant Road? The major north-south streets (Oracle Road, 1st Avenue, and others) still have permissive dual lefts for the NB-to-WB and SB-to-EB movements.

Saw them in construction during May and June while doing asphalt sampling and coring for a geotechnical firm.  They require a substantial amount of additional area in the form of a "bulb out" in order to allow large vehicles to U turn.  Also create additional signals and delays for E-W Grant traffic.   Suspect that these are experimental and will not be duplicated elsewhere in Tucson.
« Last Edit: November 01, 2018, 10:28:12 PM by DJStephens »
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Roadwarriors79

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Re: Protected Left Turns in Tucson AZ
« Reply #26 on: November 02, 2018, 12:06:03 PM »

What do you think of the indirect left turns or "Michigan lefts" planned or in use along Grant Road? The major north-south streets (Oracle Road, 1st Avenue, and others) still have permissive dual lefts for the NB-to-WB and SB-to-EB movements.

Saw them in construction during May and June while doing asphalt sampling and coring for a geotechnical firm.  They require a substantial amount of additional area in the form of a "bulb out" in order to allow large vehicles to U turn.  Also create additional signals and delays for E-W Grant traffic.   Suspect that these are experimental and will not be duplicated elsewhere in Tucson.

Other than the major intersections and Grant (which may or may not include Swan Rd), the only other one under construction is at Kolb Rd and Valencia Rd. This is an intersection that I think would have been better served with a grade-separated interchange, or at least a flyover ramp. The heaviest turn movements are EB Valencia to NB Kolb, and SB Kolb to WB Valencia.
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jakeroot

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Re: Protected Left Turns in Tucson AZ
« Reply #27 on: November 03, 2018, 04:37:43 AM »

Suspect that these are experimental and will not be duplicated elsewhere in Tucson.

Probably right. These work very well as part of a coordinated corridor (MI has many examples), but only OK at single-use intersections like here.
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Roadwarriors79

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Re: Protected Left Turns in Tucson AZ
« Reply #28 on: November 03, 2018, 11:18:36 AM »

I don't know if the "Michigan lefts" will get Grant Rd widened any sooner or not. I have seen schematics for future widening projects planned on Broadway (from Euclid Ave to Country Club Rd) and 22nd St (from I-10 to Tucson Blvd). The widened roads would have dual left turn lanes at intersections with other major streets.
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DJStephens

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Re: Protected Left Turns in Tucson AZ
« Reply #29 on: November 03, 2018, 12:48:58 PM »

The Grant Road project that I was on was Phase II (Stone to Park). It was being reconstructed as a four lane divided arterial.   The ROW appeared wide enough to go six lanes, but do not believe maximum width was a goal of either Phase I or II.   Pedestrian safety, bus pull outs and complete curb and guttering seemed to be the goal.     
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Roadwarriors79

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Re: Protected Left Turns in Tucson AZ
« Reply #30 on: November 03, 2018, 01:24:36 PM »

The Grant Road project that I was on was Phase II (Stone to Park). It was being reconstructed as a four lane divided arterial.   The ROW appeared wide enough to go six lanes, but do not believe maximum width was a goal of either Phase I or II.   Pedestrian safety, bus pull outs and complete curb and guttering seemed to be the goal.   

It will be six lanes (eventually). Check out this video (near the end of construction of the Stone-to-Park segment):

« Last Edit: November 03, 2018, 09:19:10 PM by Roadwarriors79 »
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tradephoric

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Re: Protected Left Turns in Tucson AZ
« Reply #31 on: November 03, 2018, 03:22:32 PM »

^That video of Grant Road does appear to be the first Median U-Turn corridor outside of Michigan.  Now the side-streets still allow direct lefts onto Grant Road so it's not exactly what you would see in Michigan (where all left turns are restricted at the main intersection).  A Median U-turn corridor is really a combination of the two intersection designs below (which is basically what you see in that Grant Road video).  Now the Median U-turn corridor along Grant Road only appears to last a few miles where in Michigan the longest Median U-turn corridor extends over 30 miles along Telegraph Road.. but it's a start!





Here's a video all about Median U-turn corridors.  The guy at 2:30 talking about Woodward avenue who says "you can make it down Woodward quite quickly" isn't lying.  To prove it, I posted a video of a 40 mile drive down Woodward avenue driving BOTH directions, traveling through 124 traffic signals without getting stopped at a single red light.  Say what you want about Michigan lefts, but they really do help with good signal progression along the corridor.





« Last Edit: November 03, 2018, 03:40:41 PM by tradephoric »
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jakeroot

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Re: Protected Left Turns in Tucson AZ
« Reply #32 on: November 03, 2018, 05:34:18 PM »

Now the Median U-turn corridor along Grant Road only appears to last a few miles where in Michigan the longest Median U-turn corridor extends over 30 miles along Telegraph Road.. but it's a start!

The thing that MI will always have, that very few other jurisdictions ever will, is infinitely-wide ROWs. The widest roads in my area rarely crack 120 feet in width (curb to curb). Telegraph seems to sit around 150 to 160 feet. That extra room permits, among other things, half of the U-turn maneuver to occur in the median, so as to not require bulb-outs, which are often required at non-MI Median U-turn intersections.

That said, I think some of the bulb-outs are unnecessarily large (those along Grant, above, for example). A truck needing that much room to turn around, may as well be allowed to turn left at the intersection, or (if leaving a parking lot and being forced to turn right), turn left onto another road and come back. A corridor with thousands of trucks should probably just use standard lefts.

Pierce County, WA has built several roads that use U-turns to facilitate some movements. Canyon Road, which has quite a few normal lefts but many U-turn lefts for side streets, doesn't have any bulb-outs because there's three lanes for through traffic, but another (176 St) has bulb-outs, though they are much smaller than those built in Tucson, for example. I have seen trucks perform U-turns along these corridors (it's not a quick process), but it's very rare.
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JKRhodes

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Re: Protected Left Turns in Tucson AZ
« Reply #33 on: September 10, 2020, 10:07:26 PM »

The major east side intersections (22nd, Broadway, Speedway at Kolb, Wilmot, Craycroft, etc) have all gone to four head FYA left turn signals with TOD phasing as of my last visit.

In my observation the left turn signal tends to stay red until the queue of through traffic clears the intersection. Then it transitions to FYA, followed by a lagging green arrow as they've historically operated.

The five-head FYA for right turns still remain at intersections where they were previously installed. Odd to see a "tucson experimental" signal treatment and a new MUTCD standard being used at the same intersections.
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