What are rules on taxi 'carpooling'?

Are taxi drivers allowed to have their family members in the cab when they pick up passengers?

I was at a taxi stand at Singapore General Hospital one late afternoon when a cab, with the sign "Tampines", pulled up.

A woman was sitting in the front passenger seat, so I asked who she was. She turned out to be the wife of the driver.

I was not comfortable with this and took the next cab instead.

Are taxi drivers allowed to "carpool" this way?

Amy Choong (Ms)