A confluence of factors, including tighter security measures in the face of terrorist threats, resulted in the hours-long jams at the Woodlands and Tuas checkpoints.
Spikes in the volume of travellers during the holiday period, as well as unpredictable traffic situations, played a part as well, according to the Immigration and Checkpoints Authority (ICA).
But measures are in place to ease waiting times, like having more staff at checkpoint counters during the festive period.
ICA officials explained yesterday at a media briefing at the Woodlands checkpoint the reasons behind the Causeway traffic jams that led to congested pedestrian lanes on Thursday, when hundreds of commuters from Malaysia tried to cross on foot.
Bus drivers stuck in traffic opened doors for commuters to spill onto the roads, adding to the congestion, as there is no proper footpath for them on the Malaysian side of the Causeway, said Alan Koo Weng Yew, the Woodlands commander of the Integrated Checkpoints Command for land.
He also pointed to arriving motorcyclists as a source of congestion. There are four motorcycle lanes on the Malaysian side of the Causeway but only three on the Singapore side.
Some motorcyclists ride on lanes for cars, lorries and buses after clearing Malaysian immigration and try to cut back into the motorcycle lanes at the Woodlands checkpoint.
Lane discipline on the Malaysian side of the Causeway cannot be enforced by ICA. But ICA said one way it manages traffic is through the cross deployment of staff to areas where resources are needed the most.
"If, for example, we see that motorcycle traffic is building up very fast, we will convert a car zone to accommodate the higher demand of motorcycle traffic," said Assistant Commissioner Koo.
An estimated 430,000 travellers cross the checkpoints daily during the year-end school and festive holiday period, compared to an estimated 400,000 during non-peak periods.
About 100 ICA officers have been working overtime this holiday season to deal with the increased volume of traffic, said ICA. Manpower is planned months in advance of the holiday season, but the traffic situation is volatile, with unpredictable spikes throughout the day, the authority said.
One tax on its resources has been the higher number of travellers who have tried to cross the checkpoints into Singapore with wrong, invalid or missing travel documents.
There were 3,500 cases between January and October this year, up from an estimated 3,400 last year.
But ICA has introduced a measure that could reduce wait times.
Customs checks are now conducted just before immigration counters, which eliminates the backflow of vehicles waiting to enter lanes for security checks after immigration, and creates a longer distance between Customs and the checkpoint exit for those who may try to dash through, said ICA.
The move was introduced at the Tuas checkpoint on Sept 21 and at the Woodlands checkpoint on Dec 1.
Minister for Home Affairs K. Shanmugam, who visited the Woodlands checkpoint on Saturday morning, said that manpower has been increased to accommodate the higher volume of traffic during the holiday season.
"Based on the increased manning, all or most counters are open," he said.
Addressing the reported four to five hour wait times, he said: "I think earlier (last week), there was a bigger crush; but it is unlikely that it was four to five hours on the Singapore side. It is likely to include waiting time on the Malaysian side as well. Our own records suggest that on our side, at most it will be two hours plus, under three hours."
He added that people understand that ensuring the safety of Singapore and its people is ICA's "foremost priority", following the Paris terrorist attacks and heightened terrorist threats worldwide.
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