As it turns out, I have the answer key - a 1969 street directory :-)
1) The roundabout at the junction of Queensway and Commonwealth Avenue was known as Queenstown Circus of course.
Close. The official name was Queens Circus Ironically, during the construction of the Queensway underpass here a temporary roundabout was recreated here.
2) The roundabout at the junction of Queensway, Farrer Road and Holland Road was known as Holland Circus.
Could be. It's unnamed in the street directory.
3) The roundabout at the junction Alexandra Road, Queensway and Jalan Bukit Merah was known as Alexandra Circus. Actually I am just guessing here.
Ha ha ! Good try but this one is tough. The correct answer is Rumah Bomba Circus, i.e., Fire Station Circus, probably named after the nearby Alexandra Fire Station.
4) The roundabout at the junction of Lorong 1, 2 and 6 Toa Payoh was known as Toa Payoh Circus. This was also a very huge one in terms of area - almost as big as the one at Queenstown.
I remember this Circus being there as far back as I can recall, but surprisingly it's not shown in the 1969 directory (below).
Both the circus and the flyover must have been built around 1970, and are shown below in the 1981 street directory
Somebody also mentioned a roundabout at the junction of Lorong Chuan and Braddell Road. I don't remember that at all, but it's there in the 1969 directory.
5) The roundabout at the junction of Bukit Timah, Clementi and Anak Bukit was known as Bukit Timah Circus.
7) The roundabout at the junction of Anak Bukit and Upper Bukit Timah Rd was known as Ewart Circus.
Strangely enough, both of these circuses (circi ?) were marked as Bukit Timah Circus in 1969. Probably a typo.
By 1980, though, the northerly one at Anak Bukit & Upp Bukit Timah is marked as Ewart Circus.
6) The roundabout at the junction of Serangoon Road, Macpherson Road and Bendemeer Road was known as Woodsville Circus.
Probably. Unnamed in the street directory.
8) If you guessed that the roundabout at the junction of Lornie Road and Thomson Road, just in front of the entrance to MacRitchie Reservoir was known as MacRitchie Circus, you are only half correct. The correct answer is Bulatan MacRitchie. Why the special use of a Malay word for roundabout? I don’t know. ... Actually, there was another roundabout just a hundred metres or so away at the junction of Upper Thomson Road and Braddell Road.
Yes. I've included Braddell Rise school in this clipping as well.
