This is a prediction for a potential HLL, which connects Tengah New Town to the city centre and eases crowds on the EWL and DTL, based on this map.
HL1 Tengah West
HL2 Tengah
HL3 Bukit Batok Hillside
HL4 Bukit Batok
HL5 Bukit Batok East
HL6 Toh Tuck
HL7 Clementi North
HL8 Sunset
This can be a potential interchange with CRL.
HL9 Pandan Valley
HL10 Jelita
HL11 Holland Village
HL12 Holland Park
HL13 Dempsey
HL14 Napier
HL15 Paterson
HL16 Great World and HL17 Killiney
HL18 Fort Canning