506 loading is pretty decent. 518 loading is quite crap. I
really don't see the need of DDs on 518 except weekends.
506 on the other hand does have good long distance travelers.
Even if bus takes around 60 pax still worth putting DDs because of
the long distance.
502 also has decent loading when you observe at MBS. The SDs get
50-60 pax. Wouldn't mind upgrading a few SDs to DDs.
518 on the other hand is very random. I have seen few SDs depart
MBS with 20-25 pax and then few with 40-50 pax. Never really see
high crowds in PM unless it is weekend (which also is random).
Weekend loading for 502, loses out to 518, quite
unexpectedly.
This may explain why 502 received less DDs for AP
shift.
However, it is true 502 receives higher loads during PM peak, as
it stops by Tanjong Pagar near Anson Rd before hitting the express,
hence drawing office crowds. 518 however already hits the highway
before reaching the CBD.
SBST may consider adding more split DDs on 502 at this time.