I'm sure that I'm going against some fundamental laws of PLC instruction, and that is something I'm still trying to learn. However, it works.
How many times have I heard "but it works!" from students. Really it appears to work. Visually it is correct, but techically it is incorrect. The LogixPro Traffic Light problem has hundreds of solutions that will run without crashes, but only a few solutions that meet all the specifications.
Look at the attached timing diagram for your Post #21 program. The previous timing diagrams were for the program AS IT SHOULD BE, but this one is LIKE YOURS (except for the 1-second red time correction noted below).
Do you see the difference between what happens from: YELLOW WEST light to RED NORTH light (2 seconds overlap of both reds), and from YELLOW NORTH light to RED WEST light (Red West is ON for 2 seconds after Yellow, but Red North is not)? Look at it until you see that the two directions are not identical - it is "one-sided" with an overlap of reds on one end but not on the other end. Also Red West is ON 2 seconds longer (16 seconds total) than Red North (14 seconds).
The above actions should be identical as to timing and sequence of events (but for different directions). They are not, although the program appears to work just fine and dandy. The reason is that in this case there is nothing in the LogixPro graphics program to detect the difference. However, in many PLC programs, if the logic is not "parallel" for two sides of the same "coin", the program will not work properly. This only matters if you later add something that DOES depend on the program being "symmetrical".
For example, if you add the Left Turn option in the advanced traffic light program, then suddenly the difference betwen the two light directions in your program will make it difficult to arrive at a way that will work for both N/S and E/W directions - due to the fact that your red lights only overlap on one end, but not on both ends. Also, technically the overlap is supposed to be 2 seconds, not 3 as you have it (I corrected that in the timing diagram).
In the real world, many traffic lights have green lights that stay on longer in one direction (thus reds lights that stay on longer in the tangential direction). But for this problem, the instructions state the SAME times for boths reds, both greens, and both yellows. You have not achieved that symmetry for your red lights.