THE traffic congestion caused by Shell's $1 per litre promotion last month was "not acceptable" in certain areas, said Transport Minister Raymond Lim.

While most roads remained passable for traffic on October 24, the Land Transport Authority (LTA) had to take measures like adjusting traffic light timings and making public broadcasts to ease congestion in badly-affected places, he said.

Shell was also instructed by LTA to deploy additional resources to manage the traffic conditions, while the Traffic Police instructed the petrol giant to end the promotion early at one of the stations.

Mr Lim was responding in writing to questions for Monday's Parliament sitting posed by Dr Lim Wee Kiak (Sembawang GRC), Dr Muhammad Faishal Ibrahim (Marine Parade GRC) and Mr Seah Kian Peng (Marine Parade GRC).

He said that commercial promotion events on private premises, like the one held by Shell, do not require specific approvals from the Government.

However Shell did inform the Police and LTA beforehand and implemented measures recommended by the authorities, like hiring Auxiliary Police Officers to control traffic.

On its own, Shell also increased the number of pump attendants and cashiers to speed up service on the actual day, and excluded stations where queues would pose serious safety risks.

"However, the promotion proved to be more popular than Shell had anticipated," Mr Lim said.

"This unfortunate incident has heightened the awareness of commercial entities on the need to be more socially responsible when planning their commercial events in future.

"Better planning of events, as well as the provision of more resources for crowd and traffic control can be expected of organisers of future promotional events.

"The LTA and Police will also work with the organisers of such events to see how best we can minimise a recurrence of such traffic incidents," he said.