Inflatable seals will be installed in the doors of 90 older MTR trains to keep out noise.
The project will cost HK$200 million and chief of operations engineering David Leung Chuen-choi estimated it would be completed by 2020.
The trains to be fitted with the seals were from Britain and were the oldest ones in the company. Some had been running from 1979, when the railway opened, he said.
Leung said three trains on the Tseung Kwan O Line had been fitted with the seals and had gone through tests recently. Noise in their compartments was found to have been reduced, but he could not estimate by how much.
About 30 trains on the Tsuen Wan Line will be the first to have the seals installed, followed by others on the Island and Kwun Tong lines. Leung said the work on Tsuen Wan Line trains could be contracted out this year, and could start next year.
The seals expand after the train doors are closed, filling the gap between the train body and doors. "We found the in-cabin noise was significantly reduced," Leung said.