While the Cross Island Line is expected to be ready only in 2030, studies will start at the end of this year to plan for Singapore's most ambitious MRT project yet.
The 50km line runs from Tampines to Jurong, passing through densely built-up areas such as Sin Ming, Hougang, Clementi, and beneath the Bukit Timah Nature Reserve and Central Catchment Area.
The LTA is planning well ahead of time because contractors will need to dig deeper underground in land-scarce Singapore for new rail projects.
The pace of construction will also depend on the ground's soil profile, which experts say changes every 2 to 3 metres.
This makes excavation works all the more challenging as the tunnel-boring machines move through different types of rock and soil, said Ms Choo Chai Foong, LTA's deputy director for design development (rail).
Ms Choo, who has been with the LTA for 16 years, said: "As stations get deeper, we must be more careful as there will be more risks and engineering methods need to be adjusted."
The LTA will not want a repeat of the tragedy in April 2004, when a deep excavation at a Circle Line worksite collapsed, killing four workers and causing a section of Nicoll Highway to cave in.
That delayed the progress of the Circle Line by around two years and consequently, the rollout of lines that were to come after it.
But Singapore is not the only city to experience delays in rail projects.
Paris' plan to double its network by building some 200km of new lines took years to be finalised and approved.
New York City's Second Avenue Subway project had been planned since 1929, but only got under way in 2007.