My Level: 2
Reason for request: Add sub road
downlocked 
I am not sure if this is over engineering of the route?
I think you can simply use a two way street and add the allow U-turn to simplify the mapping.
I would say both work but personally I will use what has already mapped. Using 2-way road and allow u-turn is OK but sometimes it doesn’t work with unknown reason. Mostly there is a bug internally in the app or Waze changes the routing algorithm. In the UK, we asked Waze to disable u-turn. Sometimes it works, sometimes it doesn’t. So personally I do not rely on disable/enable u-turn.
I think the u turn have higher penalties, such that the algorithm is not likely to use unless the routing will result in great detour.
I haven’t tested this route after I drew it 
but I rarely see 2-way roads with u-turn enabled in HK, so I just follow how other editors drew existing road networks - split the road into two 1-way and then add a u-turn ramp.
I see 2-way roads with u-turn enabled being more commonly drawn in mainland China and Taiwan because almost every single traffic light junction allows u-turn, whereas in HK 99% of traffic light junction doesn’t allow u-turns. Sadly I don’t drive often enough in China/Taiwan to tell whether such way of drawing u-turns actually works effectively.
I just tested with a two-way street with the “u-turn” arrow set to green.
If you are approaching a dead end (cul-de-sac), even if the u-turn arrow remains as red (default), Waze still assume a u-turn is allowed at the end of the dead-end street.
Waze will never give you a “u-turn” instruction where a u-turn is required. The distance count-down shows the distance to the next action after the u-turn. For example, if the dead-end street is 300m long, the distance countdown will start from 600m, as you need to drive 300m to the dead-end, make a u-turn and then drive 300m back to join the main road. It all seems logical up till this part, since I have no choice but to make a u-turn at the end of the street.
Now it comes the problem which I believe is a program bug. If I set a two-way street with the “u-turn” arrow set to green, even if it is in the middle of a long straight road (not a dead-end), Waze behave as if it is a dead-end street, i.e. No explicit “u-turn” instruction at the junction where u-turn is required. The distance countdown is still 600m to the next action. It is only on the graphical map below, that I can tell visually a u-turn is required.