The BTS has apologised for a technical breakdown between the Chit Lom and Siam skytrain stations Wednesday morning that left hundreds of commuters and tourists stranded in all-day frustration.
The operator admitted announcements about the disruption failed to reach enough people.
Many passengers unaware of the disruption were caught in queues that extended to footpaths under some skytrain stations.
They were waiting to squeeze into overcrowded trains that arrived infrequently.
BTS director Anat Arbhabhirama said train technicians and staff did their best to bring the disrupted service back to normal and announce the delays to commuters.
Reports on Twitter indicated many foreign passengers complained that BTS employees only made status updates in Thai, leaving tourists and expats in the dark. BTS posted only two updates to its Twitter feed Wednesday morning.
Mr Anat said he realised the breakdown had inconvenienced passengers. "We want to express our sincere apologies to our valued customers for the inconvenience," he said.
Regular services are expected to resume this morning.
The BTS, which is hired by City Hall to run the skytrain service which covers more than 23 kilometres, is not obliged to compensate people in this case, but passengers could receive refunds, he said.
The concession contract does not stipulate a fine if problems with the BTS service cause inconvenience for its passengers. It only requires the need to set up a committee, chaired by a deputy Bangkok governor, to supervise the contract, said a source at City Hall.
The BTS must report and answer questions raised by the committee during meetings which will be held every six months.
One reason there is no fine imposed in the case of service disruptions is they "will directly affect BTS revenues, so the company has to carefully oversee its service", Mr Anat said.
The BTS had reported rail switching problems on a spot between the Chit Lom and Siam stations since Tuesday night.
Technicians were unable to solve the technical fault before the following morning and needed to stop work during the train's operating hours, according to the BTS.
The breakdown cut the frequency of train services in half, delaying train arrivals from the normal two to three minutes to five to six minutes and broke the single Sukhumvit Line into two segments: Bearing to Siam, and Siam to Mor Chit, forcing all passengers to switch trains at the busy interchange with the Silom Line.
Services on the Silom Line, which links Bang Wa to National Stadium, were unaffected by the technical failure but suffered the same congestion.
Some passengers resorted to taking motorcycle taxis during the chaos, but were charged high fares, said Land Transport Department chief Sanit Phromwong, following complaints in many areas.
Motorcycle taxi drivers found to have overcharged passengers were fined 500 baht each. They were also ordered to attend three-hour training sessions, he said.
He said offenders will have their licences suspended or revoked if they are caught overcharging again.