Even if you're right. That's only true if every one will do that but the reality is everyone's waiting on one line and you're cutting... if there a long line to get on a bus or a ride ave everyone's waiting on one line and you think it would be faster if there was 2 lines so you just walk up to the front and go on... Let's see how that goes?
And with that comparison it shows you are missing the bigger picture, just like the original picture was.
See here:
All commuters in NY are going from B-C on the highway. Some are taking exit A, so they are going from B-A.
If all commuters turning right in exit A stay in the right lane traffic will back up to B and all commuters going from B-C hit traffic due to the right turn lane in A being backed up. But if the commuters taking exit A ALL used both the right and the left lane traffic would flow faster on the highway and commute times in NYC would be faster because of it.
This is how I understand traffic flow. A real expert can way in differently but at least you can see the logic here.
The 2 lines in your bus story had nothing behind them, this case does...