COMPLEX TRAFFIC PATTERNS
Split Phases and Protected left-turn phases
Strategies to deal with / adapt for split and protected left-turn phases:
- Split phases: traffic in one direction of a street is allowed to go straight-through, right or left while traffic in the opposing direction waits (to allow for drivers to turn left without opposing traffic).
- Protected left-turn phases: left-turners (often from opposite directions) proceed while straight-through traffic waits (often this is accompanied with perpendicular right-turning traffic permitted with green arrows)
NOTE: Split phases and protected left are used when there is heavy left-turning traffic.
In these situations, the left-turning drivers have a green arrow which gives them the right of way over the pedestrians (if there is a pedestrian signal, it indicates “Don't WALK”). For a discussion on rights of way and the law for pedestrians, see "Do blind people need to determine or pay attention to the status of the pedestrian signal?"
- Wherever split phases or protected left turns are possible, cross with the surge of the "nearest parallel traffic" to ensure no crossing conflicts with left-turning traffic which has the right of way.
Split phases and protected left turns are possible (and this crossing strategy should therefore be used) not only at those intersections which are known to have split or protected left-turn phases, but also at intersections which are unfamiliar or have actuated left-turn lanes.
"Nearest parallel traffic" means
- the southbound traffic when crossing to/from SW and NW corners;
- the north-bound traffic when crossing to/from NE and SE corners.
NOTE that the nearest parallel traffic may be either coming toward the pedestrian or traveling in the same direction as the pedestrian.
In the illustration to the right, the "nearest parallel traffic" for pedestrian #1 (crossing north from the SE corner) as well as pedestrian #2 (crossing south from the NE corner) are the vehicles marked in black going north in the parallel street.
- DO NOT use stopped traffic on the perpendicular street -- or even a red signal for perpendicular traffic -- to conclude it's time to cross!
Perpendicular traffic sometimes stops for reasons other than a red signal (such as traffic congestion, or stopping to let off passengers or wait to turn left), and often a red signal for perpendicular traffic does not mean the traffic and pedestrians can cross it -- for examples see
- "Predicting crossing time by using stopped perpendicular traffic after observing the traffic pattern / signal cycle"
- Can we trust that when traffic stops at a signal, it's time for pedestrians to cross?
Lead Pedestrian Intervals (LPI's) and Exclusive Pedestrian Phases
Strategies to deal with / adapt for LPI's and exclusive pedestrian phases:
- Lead Pedestrian Intervals (LPI): pedestrian WALK signal starts 3-10 seconds before vehicular green signal (see "LPI -- A solution we've been waiting for!"
- Exclusive pedestrian phases: provides for pedestrians to cross with all vehicular traffic stopped (but right-turn-on-red may be permitted)
Lead pedestrian intervals and exclusive pedestrian phases are beneficial to pedestrians, especially at intersections where there is heavy right-turning traffic, because they reduce the likelihood of conflicting traffic during the crossing. However, it is difficult or impossible for blind pedestrians to recognize when the pedestrian walk phase begins unless the pedestrian signal is made accessible.
- LPI and exclusive pedestrian signals require Accessible Pedestrian Signals for blind pedestrians to be confident that they are beginning their crossings during the walk interval.
- DO NOT use timing to predict onset of pedestrian signal! For rationale with an example, see "Predicting crossing time by observing the timing of the signal."
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