One of the points is the turning constraints along its route. For
example, 858 cannot use bendies for this route because of the
turning constraints at Changi Airport PTB.
Svcs 920, 922, 945, 947 are still allowed to use bendies in the
event that any of their perms had breakdown.
Sv 171 are allowed to use 1 bendy when there is any major events
going on at Suntec City eg. PC Show.
The services using bendies (that I had seen, not all):
61, 67, 82, 106, 160, 169, 171, 172, 176, 179,
180, 184, 187, 188, 189, 190, 300, 302,
700, 700A, 800, 804, 806, 811, 812, 851, 854, 856, 857,
859, 864, 900, 901, 902, 903, 911, 912, 913, 920, 922,
945, 947, 960, 962, 963, 964, 965, 969, 980, NR1, NR5,
NR8