SINGAPORE - Bus firms SBS Transit and SMRT have earned a combined $3.4 million in incentives under a trial "carrot-and-stick" scheme to get operators to improve service reliability and reduce bus bunching.

The monetary awards were given for bettering the regularity of 45 bus services, said Transport Minister Khaw Boon Wan on Tuesday (Feb 28), in a written reply to a question filed by by MP Liang Eng Hwa in Parliament, regarding bus reliability.

SBS Transit earned $2,040,000 for improvements to 25 service, while SMRT Buses earned $1,403,300 for improvements to 20 services.

Mr Khaw said there was a 20 per cent reduction in average additional wait times for these bus services, over the nine-month evaluation period from December 2015 to August 2016.

The Land Transport Authority (LTA) also said on its website: "Commuters benefited as wait times were more regular, bus loads were spread out more evenly and bus services were more punctual."

This is the final assessment period of the Bus Service Reliability Framework (BSRF) pilot, which started in February 2014.

Under BSRF, operators are given monetary incentives for reducing commuters' excess waiting time - the difference between actual and scheduled waiting times - or handed penalties if this waiting time increases.

The framework also uses an "On Time Adherence" standard, which measures the proportion of times that the bus service arrives less than two minutes earlier or five minutes later than its scheduled timing.

BSRF is now incorporated into the bus contracting model, which the bus industry made a full transition to in September last year (2016).

Mr Khaw said that the baseline standards under the BSRF have been tightened, following the trial.

From September, BSRF has been implemented for 108 services, and a 15 per cent reduction in average additional wait times has been observed, he added.