A project to extend the Thomson- East Coast Line north into Johor Baru is gaining traction, with the second phase of an advanced engineering study under way.

In response to queries from The Straits Times, Singapore's Ministry of Transport said the study will take up to the second quarter of 2018 to complete. But it could be completed by the third quarter of next year, it said.

Both Singapore and Johor launched the joint study in April.

"Phase 2 is intended to develop the detailed engineering design for the rapid transit system project," a ministry spokesman said.

The Straits Times understands that this stage of the study will include a detailed look at the feasibility, merits and cost-effectiveness of various alignments, number of stops and whether the straits crossing will be made under the sea or via a bridge.

The project was first announced in 2010 by Prime Minister Lee Hsien Loong and his Malaysian counterpart Najib Razak. The Land Transport Authority (LTA) said then that the cross-border rapid transit project would be an extension of the Thomson-East Coast Line, and would be completed by 2018.

This was pushed to 2019 when Singapore decided to lengthen the Thomson-East Coast Line.

Since then, there had been little progress reported on the 4-5km extension, with Singapore saying it was waiting for Johor to decide on the location of its terminal station.

But last August, Malaysia confirmed that the station terminus would be in Bukit Chagar, just north of JB Sentral. The Bukit Chagar terminus will have its own customs and immigration facilities, according to the New Straits Times.

Separately, the LTA said it embarked on a ridership study of the Singapore-Johor Baru extension last month.

It said the study is expected to be completed by the end of the year. Construction industry watchers said the line is unlikely to be completed before 2020.