Split phasing signal with pedestrian crossing - an interesting application

[mrsman]

Split-phasing, where eastbound traffic has a green and a left at a totally separate time from westbound traffic is implemented in a lot of places where there is heavy left turning volume and the use of an option lane.  Since the eastbound and westbound greens are separate, there is generally more delay for each approach than a more standard approach where eastbound and westbound greens occur at the same time.  The delay is compounded when a pedestrian is crossing the street, since the pedestrian time is usually combined with only one of the approaches.  THis means that the amount of time for the eastbound signal is increased longer than the cars need, and at the same time westbound cannot take advantage of this extra time.  Further delays for all approaches.

I recently came across an intersection that came up with a brilliant way to address this issue:

The intersection of Connecticut Ave and Saul Rd in Kensington, MD.

GSV:  https://www.google.com/maps/@39.0155199,-77.0789128,3a,75y,235.08h,93.07t/data=!3m6!1e1!3m4!1sg1lDWja9C9QtYu3db_BnAQ!2e0!7i13312!8i6656


Connecticut Ave. (CT) is a really busy north/south street.  3 lanes each direction and left turn lanes.

Saul is a narrow street.  East of CT, it serves a local neighborhood.  West of CT, it is a major shortcut that connects to Cedar and which leads to major employment cetners (NIH and Walter Reed).  There is a considerable amount of traffic on Saul that wants to turn left on CT, but no room for left turn lanes.  The eastbound Saul to northbound CT left is much busier than the westbound to southbound left.

The intersection is set up with a crosswalk crossing CT on the south side of the intersection only.

When the pedestrian button is not pressed, this operates like a normal split phase.  First eastbound gets a green with a simultaneous left arrow (4-section head).  Then, wesbound gets a green with a simultaneous left arrow (5-section head).

When the pedestrian button is pressed, the following occurs.   First eastbound gets a green with a simultaneous left arrow (4-section head) and the pedestrians get a walk signal.  The eastbound signal will terminate while the pedestrians are still crossing (likely in the FDW phase) and then, the westbound signal operates with a green ball only.  There is a sign that reads "Left turns yield to pedestrians on green (green ball)."

By combining the pedestrian phase to occur during both the eastbound and westbound phases of Saul, the traffic dept. is able to minimize the amount of red time that CT faces.  When the pedestrians are crossing, left turns from westbound to southbound have a turn that is protected from oncoming traffic, but not from the pedestrians.  Eastbound to northbound, the much heavier movement, gets a fully protected left turn during the pedestrian crossing time.

[johndoe]

Cool, thanks for sharing.  I do have to wonder why they don't opt for FYA on the side streets.  This would remove the split-phasing and could give lagging protected EBL in heavy cycles.  You'd also be able to omit permissive lefts when peds are present, if desired.

[jakeroot]

Almost identical to what Federal Way, Washington did at this intersection: https://goo.gl/8wDT1k (except Federal Way went with flashing yellow arrows)...

When the pedestrian crossing is activated, the side without conflicting green arrows gets a green (opposite camera, in the video below), but the other side gets a flashing yellow arrow. So left turns can proceed at the same time that traffic from the other side is proceeding with their movements.

https://youtu.be/jEVhAABx0q4