If the taxi industry wants private-hire operators to compete on a completely level playing field, then they might have to contend with Uber and Grab drivers being allowed to pick up street-hailing customers.

Senior Minister of State for Transport Ng Chee Meng told Parliament yesterday that 80 per cent of taxi- driver trips are street hails.

"If you completely level the playing field, it means that the private- hire cars will have street-hail privileges as well," he said. "This will not bring necessarily the outcomes we desire."

Mr Ng was responding to questions from Ms Lee Bee Wah (Nee Soon GRC) on whether there has been "any measurement to show that Uber and GrabCar actually bring positive impact to our commuters".

"If not, then why should we have them in Singapore, and create so much unhappiness among the taxi drivers?" she asked.

Mr Ng said: "We follow industry practices as best as possible.

"For commuters' interests, if you level completely the playing field, and Uber, Grab and taxi companies become homogeneous, then we will not be able to have the innovative disruption that private-hire cars bring to the industry.

"In the morning peak hours where we have an inadequate supply of full-time taxi drivers, many of the commuters' interests are served because there are supplementary drivers that come in the form of Uber and Grab, and these are mostly part-time drivers."

To a call by Mr Ang Hin Kee (Ang Mo Kio GRC) for three separate licences for taxi drivers, private-hire drivers and limousine drivers, Mr Ng said: "This was actually considered in our original design of the system. So it is possible."

But the minister said the decision to have two categories was taken to prevent the system from becoming too unwieldy.

"This is part of the whole review to make it not too cumbersome, with too many regulations, for the drivers to jump through too many hoops," Mr Ng noted.

"But it's early days yet... It will take a year to implement, so we will take your views into consideration."

The minister also said the minimum age for taxi drivers - 30 years old - "was for a different set of reasons and we are open to reviewing this if the taxi industry is requesting this level playing field in terms of minimum age requirements".

Also, he said having a minimum of two years' driving experience was adequate for private-hire drivers, but "we will continue to monitor the situation".

As for permanent residents and work pass holders being allowed to drive private-hire cars, Mr Ng said they will have to be employees of an operator.

"Today, there are no work pass holders driving for Uber or Grab," he said.