The first 10 diesel-electric hybrid buses in a fleet of 50 will be introduced on Singapore roads next month, as part of the national effort to make the public bus fleet more environmentally friendly.

They will be run by operators SBS Transit and SMRT, said the Land Transport Authority (LTA) when announcing the move yesterday.

The new buses will be deployed on both feeder and trunk services, with service 272 - a feeder service operated by SBS Transit in the Bukit Merah area - among the first routes to get the buses.

In hybrid vehicles, when the brakes are applied, the electric motor acts as a generator to recover kinetic energy, which is stored in the batteries as electricity.

The buses will run on electricity at speeds of up to 17kmh, switching to the diesel engine only at higher speeds.

The vehicles are from Volvo East Asia, which won a $30 million contract to supply the vehicles in October last year .

Two trials of a Volvo hybrid bus, conducted in Singapore in 2015 and 2016, reported fuel savings of up to 40 per cent as well as "significant reductions" in emissions of carbon dioxide and other pollutants.

On top of these hybrids, Singapore will start introducing a fleet of 60 electric buses on the roads from next year.

The hybrid buses are fitted with several features to benefit both commuters and drivers.

These include advanced driver-assistance systems to warn drivers of obstacles, while a camera trained on the driver's eyes will sense if he is dozing off and trigger a device to jolt the seat.

For commuters, an enhanced information display system will include two LCD screens that will give more information about their routes.

One LCD screen facing the outside of the bus will show the three upcoming MRT stations on the route, as well as which lines the stations are on. The other screen in the bus displays the next four stops, in addition to nearby MRT stations and their lines.

The enhanced information display system will also make audio announcements on the next bus stop.

All new buses will be fitted with this enhanced display system to help commuters plan their journeys, said the LTA.

"All these will help make the commuter experience more pleasant and encourage more people to take public transport," said Senior Parliamentary Secretary for Transport Baey Yam Keng, who rode on one of the new hybrid busesyesterday.

The buses will be progressively deployed on different services, with details to be announced at a later date, said the LTA.

"This progressive deployment will help us better understand the operational challenges that come with the wider deployment of such buses under our tropical climate and traffic conditions," it added.

Also, it will give bus technicians and engineers more time to understand the challenges of maintaining such buses, the LTA said.