Some early train commuters in the western part of Singapore had to hop onto parallel bus services instead yesterday, as later operating times kicked in at 13 MRT stations.

From now till Dec 18, train services from Joo Koon to Queenstown and Jurong East to Bukit Gombak will start at around 7am on Sunday - a change from the usual first-train times of between 5.30am and 6.30am.

The later starting times will give SMRT engineers an additional 90 minutes to carry out renewal and maintenance work. This translates to 29 additional work nights over the six months, said SMRT.

Mr Roger Lim, project director of track infrastructure at SMRT, said that in a typical night, engineers have only a 90-minute window for maintenance work, after setting aside 45 minutes to mobilise and deploy staff and equipment, and another 45 minutes to demobilise.

"We plan to intensify our re-sleepering, resignalling and third-rail replacement projects as well as carry out routine maintenance work such as track inspections, replacement of track components and the smoothening of running rails using rail grinding vehicles," he said.

Commuters who need to travel before 7am can take a parallel bus service that goes from Joo Koon MRT station to Bukit Gombak MRT station in both directions.

It operates every 10 minutes between 5.30am and 7am on Sundays. Fares are commensurate with the train distance travelled.

SMRT declined to give estimates of the number of commuters affected by the later start times.

At Jurong East MRT station yesterday, SMRT staff fanned out to remind early commuters about the later starting times.

Those redirected to the parallel bus services included nurses, factory workers as well as shift workers such as cleaners.

Factory worker Tan Geok Keng, 74, was one of the first passengers on the parallel bus service from Jurong East to Bukit Gombak. She was on her way to Woodlands for work, a trip she makes from Tuesday to Sunday at 5.30am.

"It is not that inconvenient as the trains start later only on one day," she said in Mandarin.

Nurse San Yu, 35, was running late for her 6.30am shift as it took her 30 minutes to get from Pioneer MRT station to Jurong East MRT station on the parallel bus service.

"It's usually nine minutes by train," she said.

With the later operating hours, Miss Yu, who works in a nursing home in Aljunied, has to take another bus from Jurong East to Queenstown, before boarding the train.

"I feel tired, but I don't have a choice. Train maintenance work will benefit the whole of Singapore," she said.