The Bangkok Metropolitan Administration's (BMA) Traffic and Transport Department reported a drop in the number of cars on the city's streets on Sunday's annual car-free day.
The office counted the number of vehicles on the roads around the Democracy Monument and Sala Daeng intersection on Sunday compared with the previous Sunday, Sept 15.
A total of 27,131 cars were recorded on roads around the monument on Sept 15. The number dropped by 2,576, or about 9% on car-free day. The number of vehicles recorded at Sala Daeng stood at 34,481 on Sept 15. This fell by 2,620 or 7.5% on the campaign day.
City Hall spokeswoman Treedao Aphaiwong said on Monday that the BMA will compare the two sets of figures with statistics collected next Sunday, to gauge whether car-free day was a success.
But the campaign was tainted by images posted on social media sites showing water bottles, food boxes and rubbish left in front of the CentralWorld shopping centre, one of the venues that hosted a special event as part of the campaign day.
Mrs Treedao said the BMA acknowledged the problem and would not let it happen again.
City Hall was looking at closed-circuit camera footage from the area to find out how long it was before the mess was cleaned up, she said, adding that BMA was not solely responsible for the event.
"The Thai Cycling Club was a co-organiser of the event at the shopping centre," she said.
Mrs Treedao urged critics to wait and find out how long it took for the mess to be cleared, instead of rushing to comment on the images.
"If the trash was collected within one hour, it was normal. But if it was left until the afternoon, it would be a regret," she added.
BMA has organised an annual car-free day for the past five years.
Governor MR Sukhumbhand Paribatra said on Sunday that plans to encourage city dwellers to leave their cars at home one day every month are being considered, to help improve air quality in the capital.
About 20,000 cyclists took part in the campaign on Sunday at Sanam Luang and other venues.