The Thailand Development Research Institute (TDRI) is studying how electric train fares could be adjusted along new routes to ensure fairness and affordability to all commuters.
Sumet Ongkittikul, director of the TDRI's Transport and Logistics Policy, said the results will be presented to the government.
The TDRI, he said, found that a low-income earner can afford to pay a train fare of only 11.7 baht a trip, which is lower than half the current average train fare of 28.3 baht.
A middle-income earner is capable of paying 20.3 baht per trip.
In the face of the future unveiling of new electric train routes and extensions, train fares are likely to increase unless they are curbed, he said.
If nothing is done, it is estimated the train fare from Bang Yai to Bang Na or from Bang Yai to Ekamai could exceed 100 baht, Mr Sumet said.
The TDRI recently compared the average fare per trip in Bangkok with those of Singapore, Hong Kong and London using a purchasing power parity (PPP) adjustment.
Thailand's capital had a PPP-adjusted average fare of 28.3 baht per trip, more than double the Singaporean fare of 13.3 baht.
The equivalent train fare in Hong Kong was 16.8 baht per trip.
In terms of cost per kilometre travelled by train, the average fare in Bangkok stood at 14.8 baht, as opposed to 12.4 baht in London, 2.3 baht in Singapore and 4.08 baht in Hong Kong.
According to Mr Sumet, the number of passengers in the electric train system is still lower than its commuter-handling capacity and this takes a toll on the operators which have to shoulder high operating costs.
Their burden could be eased by an increase of passenger numbers, he said.
Train fare adjustments, meanwhile, should take into account both cost and passenger numbers and efforts must be made to boost service quality, Mr Sumet said.
According to research by the Aom Money website, using the BTS electric train service is more costly than the MRT subway system and the State Railway of Thailand's Airport Rail Link.
A BTS passenger would be charged 37 baht when travelling from Sala Daeng to Asok, as opposed to 23 baht when commuting by MRT between Silom and Sukhumvit stations, which is an equivalent journey, the website indicates.