Just to add on:
If Svc 27 Tampines sector is removed, Svc 168's loading will
literally fly up sky high. Those pax who board at MRT do not only
head towards Sengkang/Hougang/Woodlands, they also head towards Ave
9. Yes, Svc 72 also heads towards Ave 9, but when you have 2
high-frequency services calling at a stop beside the MRT, will you
choose to walk further to the int to take Svc 72?
Also, M/SWT varients normally use whatever their parent route
are using. Hence even if we suggest 27M countless times and hope it
will receive DDs, the most we will probably get is full SDs, simply
because 27 is a full SD fleet service. If you need more proof of
this, look at every CGA/full-fleet SD SWT's fleet. If the PTO logic
is like this, there is nothing much we can do about it, at least
not without the whole country complaining.
And if you are wondering why SWT 139A (prior to introduction of
139M) have a crossover DD, IIRC, Svc 139 did have a DD in its
fleet. Its parent route have a DD, hence a DD is deployed.
You cannot just remove the Tampines sector... You need another
service to complement it if 27 to CGA bypasses Tampines... Also, a
lot of sv 72 pax alight along Tampines ave 9.. I wouldn't say that
people prefer 27/168 to ave 9, because with 5-7 min frequency on sv
72 from Tampines, a lot of people do take this one as
well.
I think "A" and "M" might be operated differently. M services
have dedicated buses while A services are drawn from parent
service. So definitely possible for 27M to get DDs.