ComfortDelGro will be introducing electric taxis to give passengers a cleaner ride soon. The taxi company has brought in two electric Hyundai Ioniq taxis, its group Corporate Communications Officer Tammy Tan told The Straits Times. But these have yet to hit the road as it is awaiting regulatory approval for a fast charging station.

"We will provide further details when we are closer to the launch," Ms. Tan said. She did not say how many more electric vehicles the firm intends to add to its fleet of more than 13,000 cabs.

The move will make ComfortDelGro the second operator to have electric taxis here. HDT Singapore Taxi, which began operations in 2016, runs a 100-strong fleet composed entirely of electric cabs, manufactured by Shenzhen-based BYD.

Two months ago, it applied to the Land Transport Authority to add another 800 electric taxis. Ride-hailing firms Grab and Uber also have electric vehicles.

Last year, ComfortDelGro added the Hyundai Ioniq petrol-electric hybrid to its fleet. In its 2016 Sustainability Report, it said it aimed to replace its ageing Hyundai Sonatas with 1,000 Toyota Prius hybrids. Singapore joins cities such as Amsterdam and Montreal, which already have electric taxis. In Shenzhen, 63 percent of the Chinese city's 17,000 taxis are electric. The aim is to reach 100 percent by 2020.

The continued move away from diesel engines is a positive step for taxis here, said Asian Clean Fuels Association director Clarence Woo.

He noted that the World Health Organisation classified diesel emissions as a carcinogen in 2012.

Professor Subodh Mhaisalkar, Executive Director of Nanyang Technological University's Energy Research Institute, said replacing a fossil fuel-powered taxi with an electric-powered one could mean cutting carbon emissions by 50 to 70 percent.

However, the possible impact on the electrical grid of converting the taxi population to electric vehicles is something that needs to be looked at, said Prof. Subodh.

Issues such as the source of the electricity also need to be taken into account when considering the environmental impact, said Mr. Woo. Still, Prof. Subodh said any electrification of Singapore's transportation system is a positive step.

He expects widespread adoption of electric vehicles for Singapore's bus and taxi fleets within the next five years. "Prices of batteries are dropping and their reliability is already there," he said.