Taking an MRT train that stops at just a few stations and skips the rest so that travelling time is reduced could become an option for commuters here in future.
The Land Transport Authority (LTA) will study running both normal and express trains on the Cross Island Line, which will be ready in 2030.
It is calling for an engineering feasibility study for the proposed 50km line, which will run from Jurong industrial estate to Changi.
LTA expects the consultant to propose alignments that would let the line operate with both normal and express trains, a common feature of metro systems in cities such as Tokyo and New York.
Experts say express trains are not viable on existing rail lines, as most stations have just two tracks, making overtaking impossible. Upcoming lines such as the Downtown and Thomson lines are not designed for this either.
Mr Rajan Krishnan, chief executive of engineering firm KTC Group and former LTA head of rail projects, said express trains would be useful for moving commuters rapidly from one interchange station to another, allowing them to make transfers quickly during peak hours.
Transport researcher Lee Der Horng from the National University of Singapore said an express service is logical for the Cross Island Line, which will pass through areas with lower population density.
The Cross Island Line could have between 30 and 34 stations, with nine to 12 interchange stations. It will pass through areas such as West Coast, Clementi, Bukit Timah, Sin Ming, Ang Mo Kio, Hougang, Loyang and Pasir Ris. The study would also have to determine the stations an express train should serve.
Professor Lee added: "Singapore really needs to have a much faster connection between east and west. Even though train arrival times are predictable, it can be painful to travel from Joo Koon to Pasir Ris." This journey now takes about 63 minutes, a stretch of 29 stations.
Mr Khoo Hean Siang, former executive vice-president for trains at SMRT, said having express trains would not only reduce travel time, but also ease crowding. One way to run an express service would be to have a third track at bypass stations for overtaking. This will also allow service to continue during a disruption, he noted.
But Mr Rajan said having such "pocket" tracks would mean longer waiting times for normal trains, which would be stopped till the express train has passed it far enough for a safe margin to move.
He said: "To co-exist both types of trains on the same set of tracks at the same time would be challenging, as it would compromise the service standards of the normal trains."
Instead, there could be separate dedicated tracks for normal and express trains, which would mean four tunnels and four platforms at each station.
The downside of this, said Nanyang Technological University adjunct associate professor Gopinath Menon, would be higher construction costs, as stations would have to be larger to accommodate the additional tracks.
As for fares, Prof Lee felt the Cross Island Line should not be priced differently from existing MRT lines even if it offers an express option.
He said: "There is a basis to charge more only if the train service is delivered to passengers in a different way, if there is more seating, or if the train itself is slightly different."
The engineering study will also, among other things, consider six-car and eight-car rail systems for the high-capacity Cross Island Line.
The North-South, East-West and North-East lines each have six-car systems. The Circle and Downtown Lines operate with three-car trains, while Thomson Line trains will have four.