Samart Ratchapollasit, a former deputy governor of the Bangkok Metropolitan Administration, wrote on his personal Facebook page that the cost - including construction, land and consulting - was almost equal to the high-speed train project under the 2 trillion-baht loan bill approved by the previous government.
He said the average cost per kilometre of the NCPO's proposed routes totalled 532.7 million baht for both lines, but the maximum speed was only 160 kilometres per hour, which was slower than trains proposed by the Yingluck Shinawatra-led government, which proposed speeds of 250-300 km/h.
Slower trains should mean lower costs, Mr Samart reasoned.
The proposed Nong Khai-Map Ta Phut route would be 737km long and cost 392.5 billion baht, while the Chiang Khong-Ban Phachi route would be 655km long and cost 348.8 billion baht. Both lines would use 1.435-metre standard-gauge track, which can service high-speed rail.
Mr Samart listed the average cost-per-kilometre of the previous government's plan at 456-521 million baht. He said the route between Bangkok and Rayong had the lowest average cost at 456 million, followed by 521 million baht to Chiang Mai, 553 million baht to Hua Hin and 666 million baht to Nakhon Ratchasima.
"I would like to ask the permanent secretary of transport to review the cost of these two new routes as there may have an error in the calculation," he said.