Here is the link to the Government website in Singapore. Scroll down the page to "Transportation" and the vehicle totals are enumerated by private, public transportation, and commercial. This is the most recent data, as it is from the Registrar of motor vehicles, Singapore.
if FunAdvice won't allow the Aich Tee Em Ell link here is how to get there
type the following letters in lowercase h t t p (without spaces} type a colon,followed by two forward slashes and then 3 w's followed by a dot then type singstat.gov.sg/pubn/reference/mdscontents. and the four letters h t m l ( with no spaces between the letters)