Traffic patterns

While I was driving around Tucson, I was struck by how differently the traffic lights sequenced.  (Phoenix didn’t seem to have the noticeable differences.)  Consider this intersection of Some Boulevard and No Way:

Street Intersection - augmented from image on Wikipedia
Some Boulevard is the moderately-trafficked arterial going left-right. In this intersection, left turns have to yield to oncoming traffic. The pedestrian crosswalk is better marked. Were it busier, the traffic signal at point (1) would have a red left turn arrow (indicating no turn is permitted). It might also have a dedicated right-turn lane. Currently, the pedestrian crossing signal at point (3) indicates it is safe for pedestrians to cross No Way.Starting with a green light (1) and active pedestrian signal (3), the traffic sequence here might typically be as follows.

  1. The pedestrian signal (3) changes from the white stick figure to a flashing red stick figure in peril. This indicates pedestrians should finish crossing the intersection. In any event, pedestrians should not start crossing, unless they’re in downtown Seattle, pushing a shopping cart; then, they can do whatever the hell they want because the laws of physics don’t apply.
  2. The pedestrian signal (3) turns red.
  3. The traffic light (1) turns yellow, timed long enough to permit cars already in intersection to exit.
  4. The traffic light (1) turns red.
  5. The traffic light (2) cycles: green, yellow, red.
  6. If traffic is present at position (A), traffic light (1) displays the green left turn arrow. Since this is a moderately busy intersection, it’s likely that there will be a car at the opposite side of the intersection making its left turn. On lesser trafficked intersections, if there’s no opposing traffic, the traffic light at (3) turns green, permitting traffic to move from right to left.
  7. When the left crossing traffic is done, traffic light (1) turns green.
  8. The pedestrian signal (3) will turn white. If you’re living on the east side of Seattle, it means five more cars will attempt to squeeze through the intersection, claiming the light was yellow because “the yellow bulb was still warm.”

Tucson’s sequence differed in a few, key ways:

  • Steps 7 occurs before Step 5. If you’re waiting in position A, in a Dodge Caliber, you feel despair when the light (1) turns green: the car lacks the acceleration to get through an intersection in a timely manner.  Be patient, grasshopper: the left turn arrow shines later.
  • Step 3 is measured in picoseconds. 
  • Pedestrian crosswalk signals is always red stick man.  Thus, it’s useless as a pre-warning for Step 3.

I made a few “hard stops” trying when the light changed from green straight to red.  I also observed the timing of the lights is set up so you can go east-west a lot easier than north-south.  My childhood perception that it took a long time to go short distances seemed to hold true during this visit.

1 thought on “Traffic patterns”

  1. >If traffic is present at position (A), traffic light (1) displays the green left turn arrow.

    Therein lies the rub: as near as I can tell all traffic lights are set on timers so it doesn’t matter if there’s traffic present they simply cycle the way they’re going to cycle and you, poor sod, are forced to wait regardless of the status of oncoming traffic. Do you think the pedestrian signal is measured so small to keep the U. of AZ students fit and hopping? As for the stick figure in peril…I’m shocked. We converted to the walking man and the big red hand years ago. And there’s nothing like that pedestrian countdown clock to tell those potential redlight runners just how long they have to get through the intersection.

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