Originally posted by tanjun:
For this service 139, after Toa Payoh interchange, it travels to Jalan Toa Payoh Bus stop 05 which is opposite to Trellis Towers. After this bus stop, it moves to Jalan Datoh to go to Balestier Road.
The reason why transitlink bus guide does not mention of this road because there are no bus stops on Jalan Datoh. Another example will be service 315. After 315 is moving towards Yio Chu Kang Road from Serangoon Garden Way, it uses Yio Chu Kang Road to go to Serangoon North Avenue 1. However, the transitlink bus guide also does mot mention that service 315 uses Yio Chu Kang Road to go to Serangoon North Avenue 1.
Next, I think the reason why service 139 uses Jalan Datoh instead of going to Thomson Road and then to Balestier Road because that is a shorter route than the latter.
tanjun is correct, i might add, Jln DAtoh was used to reduce bus waiting time to turn into Thomson RD and Thomson Rd back to Balestier Rd. Heavy traffic in the morning,