protected left turns vs permissive/protected left turns

[Tom895]

Protected left turns signals are converted to permissive/protected traffic signal. For example, in Socal at the intersection of Crenshaw/El Segundo Blvds had protected left turn traffic signals in both the were converted into permissive/protected left turn signals.

http://goo.gl/maps/W9dfb

[mcdonaat]

In my opinion, protected and protected/permissive each have their place. Protected-only should be used where the LOS is bad, or where the speed changes, making it hard to give good judgement. Protected/permissive should be used where LOS is good, or where people would run the light anyways.

Question on permissive/protected lights - should the right turn signal always stay green if you have the ROW? Many right turn permissive arrows go green, then yellow, then the mainline traffic turns green. Should they stay green whenever you have the right of way, and not just whenever the traffic you're interfering with has a red?

[dfnva]

In my opinion, protected and protected/permissive each have their place. Protected-only should be used where the LOS is bad, or where the speed changes, making it hard to give good judgement. Protected/permissive should be used where LOS is good, or where people would run the light anyways.

Question on permissive/protected lights - should the right turn signal always stay green if you have the ROW? Many right turn permissive arrows go green, then yellow, then the mainline traffic turns green. Should they stay green whenever you have the right of way, and not just whenever the traffic you're interfering with has a red?

Good point -- it's always annoying -- in Northern VA, VDOT uses doghouse signals for protected right turns. The light turns red forcing one to stop before the green arrow comes on. Elsewhere in VA, 3-section lights are used with green arrows that stay on even when other lights turn red.  Making pointless stops wastes gas and causes traffic issues.

[freebrickproductions]

Protected only should also be used for where you've got an extremely busy road so this way you don't have people clog up an intersection who are trying to turn left during a permissive left phase.

[hbelkins]

I've also seen protected only used in places where sight distance is questionable.

[jeffandnicole]

Question on permissive/protected lights - should the right turn signal always stay green if you have the ROW? Many right turn permissive arrows go green, then yellow, then the mainline traffic turns green. Should they stay green whenever you have the right of way, and not just whenever the traffic you're interfering with has a red?

When the arrow is green, traffic has the full right if way. When it disappears, right of way reverts to pedestrians crossing the intersection, and right turning traffic needs to yield.

[froggie]

I've also seen protected only used in places where sight distance is questionable.

A criteria MnDOT has used as well.

Page 2-6 of MnDOT's 2012 Signal Design Manual lists the criteria under which protected-only should be chosen over protected-permitted.  Among other criteria, their policy recommends protected-only if there are 3 opposing through lanes, or dual left-turn lanes, or in most (but not all) situations where the speed limit is 45 or higher (depending on the volume of left-turn traffic plus opposing traffic).

[tradephoric]

Question on permissive/protected lights - should the right turn signal always stay green if you have the ROW? Many right turn permissive arrows go green, then yellow, then the mainline traffic turns green. Should they stay green whenever you have the right of way, and not just whenever the traffic you're interfering with has a red?

Good point -- it's always annoying -- in Northern VA, VDOT uses doghouse signals for protected right turns. The light turns red forcing one to stop before the green arrow comes on. Elsewhere in VA, 3-section lights are used with green arrows that stay on even when other lights turn red.  Making pointless stops wastes gas and causes traffic issues.

Is this what you are referring to?  (Watch at 3 minutes in the video).  The green arrow will terminate for a few moments before going straight back to through green.  The problem with this setup is a driver sees the right turn arrow terminating and comes to a complete stop.  The driver then gets distracted and starts playing with the radio and fails to realize that the green ball popped up right away.  This can reduce right turn throughput as drivers are slow to get moving.

Here is an example of a right turn green arrow that terminates when the through green comes up.  Do you prefer this type of operation?  This setup can be problematic if there is a conflicting pedestrian crossing.  The green arrow would terminate for right turning drivers at the exact same time a conflicting WALK appears for pedestrians (IE. pedestrian-to-vehicle conflict with no clearance interval). 

[freebrickproductions]

Here is an example of a right turn green arrow that terminates when the through green comes up.  Do you prefer this type of operation?  This setup can be problematic if there is a conflicting pedestrian crossing.  The green arrow would terminate for right turning drivers at the exact same time a conflicting WALK appears for pedestrians (IE. pedestrian-to-vehicle conflict with no clearance interval). 

There actually is a pedestrian crossing at that intersection that crossed Hickory Hill Lane. However, there aren't any pedestrian signals at it.

[hbelkins]

Drive along US 127 in Frankfort between I-64 and downtown, and you'll see a mix of permitted/protected and protected only, and it's a crapshoot to figure out why that particular model was selected for the particular intersection.

[tradephoric]

A permissive/protected FYA with no all red phase. 

A permissive/protected FYA with an all red phase. 

[ftballfan]

Necro-bump here, but just pointing out that Washtenaw County, MI has a love affair with protected left turns. I can only think of two intersections that have permissive lefts:
US-12 (Michigan Ave) at Carpenter Rd
Huron Rd at James L Hart Pkwy

[mrsman]

A permissive/protected FYA with no all red phase. 


A permissive/protected FYA with an all red phase.

Your videos make a solid point that a short red arrow phase is a helpful way to ensure that drivers are aware of the change from protected to permitted left turns.  I agree.  And if there is oncoming traffic, it is unlikely that the left turner will find a gap here during the short red phase anyway.