if you look carefully the COE does not reduces the car population but in  fact it increased the demand of owning a car.
owning a car in Sg is expensive but it give you convenience especially if you had a family with kids.
fetching them to/from school and wife to/from office is easier than taking taxi/PHV.
with all the unreasonable surcharges by taxi/PHV, it is no more cheap alternative mean of transport for many.
high COE is here to stay.