As part of campus zoning measures to handle the COVID-19 pandemic, ISB routes were organised by zones. The DD service, introduced on 20 July 2020, connected UTown, Kent Vale and College Green/Botanic Gardens MRT to Zone D, which includes Law, LKYSPP and the rest of Bukit Timah Campus. Only students whose zone is Zone D were allowed to board DD buses.

The DD routes are not to be confused with the former D1 and D2. The new DD routes played a role similar to the former BTC1 and BTC2, connecting Kent Ridge to Bukit Timah Campus. Unlike the other routes, these routes ran at a frequency of 30 minutes all day, and ran only on weekdays.

The number was used to indicate direction; DD1 buses headed from Bukit Timah towards Kent Vale, while DD2 buses returned from Kent Vale towards Bukit Timah. For Law students, note that this is the opposite of the convention used for BTC1 and BTC2; you take DD2 into BTC and DD1 out of BTC.

OCA uploaded the following summary graphic for route DD on their website.

DD connected Kent Vale, UTown and Botanic Gardens MRT with the Bukit Timah Campus in Zone D. There was no connection to PGP or Kent Ridge MRT.

The doubled letters DD are used to avoid confusion with the previous D services. Tentatively, the DD service has been coloured purple.


Interestingly, the previous BTC1/BTC2 service operated as a single trip that originated at Kent Ridge Terminal and changed numbers from BTC1 to BTC2 when looping at Bukit Timah. However, the DD routes were two wholly separate trips, with DD1 going from BTC to Kent Vale and DD2 going from Kent Vale to BTC. This means that buses sometimes terminated after unloading passengers at BTC or Kent Vale, and did not continue as the other trip. It is also the reason why the numbering scheme was adopted – the first bus of the day would be a DD1 and the last bus of the day would be a DD2.

Some behind-the-scenes trivia related to this is that because of this arrangement, the DD drivers were typically chosen from those who drive their buses home as opposed to leaving them in NUS – this was to make it easier for them to head to Bukit Timah to start trips.


Buses permanently deployed to DD during AY20/21 Semester 1 included:

  • PC3853E
  • PC3876P
  • PC3995D

PC3983M did a few DD trips on the first week of zoning, but eventually became a CC bus. PC3906L performed several DD trips in the afternoon but as part of its daily interlining.


Following the lifting of NUS’ zoning policy on 6 December 2020, these and other zoned routes were withdrawn and replaced by the original, pre-zoning routes on the same day.


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