One hundred three-door double-deck buses will join the public fleet in batches from next year.

The Land Transport Authority said yesterday it is buying 100 of these buses for about $64 million.

Complying with the latest Euro 6 emission standard for diesel vehicles, the buses are supplied by two companies.

Fifty will come from Alexander Dennis (Singapore) for a contract sum of about $34 million, and 50 will be supplied by ST Engineering Land Systems for around $30 million.

This is the first major order of its kind, after LTA carried out a trial of three-door buses earlier.

Tower Transit operated a three-door, double-deck bus on Service 143 from March to September 2017, and SMRT Buses operated a three-door, single-deck bus on Services 190 and 901 from June 2017 to January last year.

The LTA said commuters "generally welcomed the additional door on these buses as it made boarding and alighting smoother and quicker".

A public survey of 22,000 commuters in 2016 also found 90 per cent supported having buses with a third door.

Because of the encouraging results of the trial, it called a tender to buy 100 such buses last May. The regulator and fleet owner said on Thursday that it awarded the contracts to the two companies after evaluating all bids based on criteria such as price, tenderers' experience, track record, technical capabilities and compliance with local regulations.

Both the companies are LTA's existing bus suppliers, with Alexander Dennis (Singapore) accounting for about 4 per cent of the public bus fleet here, and ST Engineering Land Systems, 23 per cent.

The new buses will arrive in Singapore in batches and be deployed on the road starting from next year.