The Transport Ministry is considering piloting a 15 baht flat-rate fare, which is estimated to require at least 700 million baht in subsidies per year, on three electric train routes, according to two service operators.
The Tao Pun-Bang Yai section of the Purple Line and the Airport Rail Link are most likely to be picked for the pilot phase of the ministry's policy to cut the cost of travelling by electric train, said Mass Rapid Transit Authority of Thailand governor Pakapong Sirikantaramas.
"These two routes are operated by the government and do not have legally binding agreements with any private parties," he said.
The government already subsidises the Purple Line at a cost of about 1 billion baht a year, according to Mr Pakapong.
"If the 15 baht fare policy is implemented on this route, the service will require between 200 million baht and 300 million baht in additional subsidies per year," he added.
Meanwhile, Suthep Panpeng, director-general of SRT Electrified Train Co, the operator of the Airport Rail Link, said last year the service earned 730 million baht in income while the cost of operation and maintenance stood at about 700 million baht.
"The 15 baht fare will mean a decrease by half of Airport Rail Link's income, hence it will need a subsidy of 300-400 million baht a year," he said.
Purple Line fares range from 14 baht to 42 baht while the Airport Rail Link's fares start from 15 baht to 45 baht.
Another route that is seen as suitable for piloting a flat rate fare is the Red Line's Bang Sue-Rangsit section which is due to begin operating by 2021, according to Mr Suthep.
"This new route will require a subsidy from the government to compensate the difference between the operational costs and the income," he said.
The Airport Rail Link carries about 90,000 passengers per day while the Purple Line serves about 50,000 per day, according to the ministry, while the Red Line is expected to have between 70,000 and 100,000 passengers per day.
The Green Line and the Blue Line, Bangkok's main electric rail routes, meanwhile, serve about 1 million passengers a day.
The Green Line handles around 700,000 passengers per day and the Blue Line 300,000 passengers each day.