Editing 1116: Traffic Lights

{{comic
| number    = 1116
| date      = October 3, 2012
| title     = Traffic Lights
| image     = traffic_lights.gif
| titletext = There's an intersection I drive through sometimes that has a forward green arrow, a red light, and a 'no turns' sign all on one pole. I honestly have no idea what it's telling me to do.
}}

==Explanation==

This comic is an {{w|animated gif}} which features an array of {{w|traffic light}}s which are lighted signals posted at intersections to control vehicular traffic. The standard North American traffic light has three solid lights: red, yellow and green (meaning, in simplistic terms, "stop", "stop if you can, otherwise exit the intersection" and "go if it is safe" respectively). More complicated lights sometimes have additional signals such as arrows indicating go or stop for a specific direction such as left or right turns.

However, as in the strip, sometimes an intersection has multiple lights with certain of them designated to apply solely to a specific lane or specific direction of travel. A common one is a left-turn light that allows the lights to stop or allow left-turn traffic independent of the rest of the traffic. Another common example is a light that applies only to public transit like streetcars that run on tracks on the city streets.

There are also other rules and features that tend to be unique to different localities as noted in the Wikipedia article for {{w|Traffic-light signalling and operation}}.

In this comic, [[Randall]] is commenting on the confusion that can be caused by having too many lights with multiple rules attached by creating an exaggerated example.

In this strip, the right light has a sign indicating that the light and the right lane are for ''left'' turners, while the 3rd-from-left is a straight or ''right'' turn lane and the 2nd from left is ''right'' turn only. In normal course, right turns would be permitted from the right lane and left turns from the left lanes. The system in this comic would have turning traffic crossing each other, as well as the straight-ahead traffic and would cause chaos (and require very complicated traffic light phases to control). The left-most light on the post has a sign indicating that left, right and straight travel are all prohibited, which is even more confusing.

The comic, as an animated gif, cycles through various phases, at first appearing somewhat normal, but then adding unusual phases. The animated gif takes about 90 seconds to cycle through the 32 discrete panels before repeating. The left post light has (unusually) left ''and'' right arrows, later becoming up and down arrows. At times the light completely shuts off, and at other times, has conflicting signals.

The third-from-left light has red ''and'' yellow, and later all three lights come on at the same time, then all three lights go yellow, and then reverse with green at top and red at bottom. The bottom light then becomes an arrow.

The fourth-from-left traffic light switches from a green light to a purple light at times.

The right light only lights red in each position.

The second-from-left light and second-from-right lights do not appear to have any quirks other than changing phases in unusual patterns.

At frames 21 and 22 (see below) the colors of the latter five lights correspond to the color sequence of the letters in the Google logo. Only the first letter of the logo, which is blue, is not reproduced on the first traffic light.

===Title Text===
The title text mentions a straightforward intersection that allows going forward but not turning. Even though Randall is confused, in some places, a red light and a forward green arrow permits going forward but disallows turns.

==Frame by frame breakdown==

[[File:traffic lights list.png]]

* 1. All traffic lights are on red, likely because the perpendicular road crossing our road has some of its lights on green. At a traffic light-managed junction, cars typically cannot cross or merge into roads that are in use from a different direction.
* 2. The traffic light of undefined purpose (pole light) switches from red to yellow. This is highly unusual, as yellow is typically used as an intermediary phase when going from green to red (<!-- presumably? -->in the US, it may be {{w|Traffic light#Meanings of signals|usual/expected}} elsewhere, in various contexts). Yellow is usually a warning light to inform drivers that the light will switch to red soon.
* 3. In switching to green, the pole light surprisingly reveals itself to point to the left. Some conventions require that all three lights in a stack have the same symbol on them, so drivers cannot be surprised by their purpose suddenly switching. This light now informs drivers they may turn left, but there is no lane that would allow them to do so. The left-most light also turned green, but it is flanked by a sign informing drivers that they may only turn to the right from here. This is a particularly contentious setup, as drivers on this lane must cross all other lanes in order to turn right.
* 4. The pole light is giving mixed messages. Maybe the red light is only relevant for cars crossing straight through? It is impossible to be sure. The fourth light also turned green, allowing people to drive straight through. The pole light and fifth light may contradict each other directly. Cars from the first lane and fifth lane would be likely to crash, unless a tunnel or bridge system is in place in the middle of this intersection.
* 5. Lane 3 and 4 are not synced. Why are they not synced? They both go straight ahead, yes?
* 6. Why did the first lane light turn off for three seconds, to then turn on again? This is not enough time for a crossing road to clear out. The fifth lane switched to amber, a distinct color in this system, although often a synonym for "yellow" (not red or green) in the context of traffic lights. People can never agree whether it's yellow or amber, so Randall helpfully differentiated the two colors. See frame 2 why it may be odd for the light to switch from red to amber. Like lane 1, lane 5 would presumably cross all the other lanes, resulting in accidents.
* 7. Oh no the first lane light is blinking between red and green. This is terrifying. The fifth lane just hangs on amber, which is probably a fair use of a warning light. The pole light is doing its own thing, better not to worry about it.
* 8. Pole light has begun blinking, light 1 continues to blink, 3 and 4 stay green, 5 continues to warn.
* 9. Light 2 joins in by turning on its yellow light. This is a common setup in Britain, to have red and yellow on simultaneously before switching to green. This allows drivers to be prepared to start driving, without yet being allowed to do so.
* 10. The pole added yellow again. Ignore it. Light 1 continues to blink. Light 2 is stuck on red-and-yellow, constantly teasing the lane 2 drivers who expect it may switch to green any moment now. Probably for the best that it won't.
* 11. Lights 3 and 4 are behaving normally, getting ready to go back to red by switching to yellow. Light 5 finally switched to the bottom light, but it's red instead of green. This is confusing.
* 12. Argh! 3 continued on to red as it should, but 3 changed its mind and switched back to green! Oh, and the pole turned off completely, which is unusual too.
* 13. The pole activates again. It should have stayed off. The arrow magically turned around, which is not possible for this type of light.
* 14. The pole continues to mess around.
* 15. The pole continues to mess around. Light 1 is still blinking, 2 is still edging, 3 still red, 4 still green, and 5 still red.
* 16. One of the arrows on the pole magically turned from green to red. A bulb near the bottom of a stack should not be red. Lane 4 switched to yellow again, maybe it will finally turn red?
* 17. Light 4 betrayed us again and switched back to green. Lane 2 now turned on its green light too, which has no meaning but it's very colorful.
* 18. Light 3 decided to join light 4 again, but now it is blue instead of green. This color is used in Japan instead of green. Light 1 stopped blinking and is now red.
* 19. Pole is still doing whatever it wants, briefly turning off its arrows.
* 20. All three bulbs of light 2 turn yellow, which I guess is a warning to us all. Light 4 teases us once again by briefly switching to yellow.
* 21. The pole is still messing around, Light 1 is still red, light 2 is completely yellow, light 3 is still blue, light 4 is back to green, and light 5 is still red.
* 22. No change at all.
* 23. The bottom bulb of light 2 turned red. This light should be green. In the sense that it should be anything at this point.
* 24. Pole is briefly off again. Light 2 reversed itself: green is on at the top now. Light 4 suddenly switched to red, no warning whatsoever!
* 25. The pole now has an "up" arrow instead of side arrows. These indicate that you can (only) go straight ahead. The center light is still <s>green</s> blue, so I suppose this is true. However, the top bulb of the pole is red too, so it's a bit of mixed messaging. Lane 2 turned off its center yellow bulb. Light 5 is back to showing amber.
* 26. Light 2 and 4 turned off completely, which is unhelpful.
* 27. The pole added an arrow "down", which is not used for traffic lights and has no defined meaning. Honestly it looks like it's outright telling the drivers to crash into eachother at this point. Light 2 is magically pointing to the right now, which I suppose is allowed because it is one of the directions that the sign flanking it allows for. Light 3 switched back to red. Light 4 is pointing left, which would probably result in crashes but is technically fine. Light 5 switched back to red. The bird, up until this point very still, moved a little bit.
* 28. Small change on the pole. 1 is red, 2 is green-right, 3 is red, 4 is green-left, and 5 is red.
* 29. Light 1, 2, and 4 are all on red. Light 3 turned itself off suddenly. Light 5 turns all three of its lights on: red, amber, and red.
* 30. The pole finally switches off for this loop. Possibly, cross-traffic can go again, with most lines either red or off. Lamp 5 is back to amber, however, which looks a bit like red.
* 31. No change from last frame.
* 32. Light 4 turns itself off too, and light 5 returns to red.

After phase 32, all lights turn back on to their top-red position. All these phases then repeat.

==Closeups on the Lights==
The following is a closeup on the lights, and the bird. The lights from left to right are here shown top to bottom. Time advances to the right.

[[File:traffic lights closeups revised.png]]

Originally, the second light had a couple frames near the start that were different. The closeup of this was as follows:

[[File:traffic lights closeups.png]]

<!-- In the light of {{comic discussion}} being removed, asking for comments at https://www.explainxkcd.com/wiki/index.php/explain_xkcd_talk:Editor_FAQ#Clarify_.22removing_Discussion_.28from_main_comic_article.29_if_it_gets_too_long.22 -->
[[Category:Comics with color]]
[[Category:Comics with animation]]
[[Category:Traffic light]]
[[Category:Dynamic comics]]