The ratio of vehicles per person in Singapore is 0.18 (compare to about ~0.5 most places in the US). It's very easy to get a Taxi to any place not accessible by public transport. I would be astounded if there is any verifiable scientific study backing this claim.
[0] https://www.lta.gov.sg/content/dam/ltaweb/corp/PublicationsR... [1] https://en.wikipedia.org/wiki/List_of_U.S._states_by_vehicle...