Hong Kong's next big railway project could be the proposed North Island Line - a controversial HK$10 billion backup subway parallel to a busy section of the MTR's Island Line.
Or it might be a new route that makes a loop of the East Rail and West Rail lines in the New Territories, by connecting the latter's Kam Sheung Road Station with the former's Lok Ma Chau.
Both could go ahead, or neither.
These are the big questions facing Aecom Asia, the firm that has been given two years to update the city's railway-development strategy and review the feasibility of several proposed rail projects, including cross-border trains linking Hong Kong and Shenzhen airports.
Some planners believe that the so-called Northern Link in the New Territories would yield the most benefits for the least money. It would greatly improve mass transit for people from Yuen Long, Tuen Mun and Tsuen Wan, while being built on mostly uninhabited land.
It would be more difficult to create the 3.5-kilometre North Island Line - which would connect Hong Kong station with Fortress Hill, and Tin Hau directly with North Point, all in parallel with the existing Island Line. And it would be a more difficult sell to the public.
But insiders say the North Island Line is the project that MTR officials are more eager to pursue.
A railway expert close to the study said the North Island Line was needed as a backup in case of breakdowns on the 26-year-old Island Line.
'No one wants to see another Yau Ma Tei incident, especially when the impact on road traffic could be much worse if it's the Island Line breaking down,' the expert said.
He was referring to a power failure in October at Yau Ma Tei station that brought chaos to tens of thousands of commuters. It forced 7,000 to take buses for part of the trip from Tsuen Wan to Central. The added bus traffic, in turn, clogged Nathan Road from Tsim Sha Tsui to Sham Shui Po.
The expert added that the Island Line, now working at about 80 per cent of capacity, would become saturated by 2026. 'It may sound like a long time away,' he said, 'but if we want it on schedule it's about time to start planning.'
The North Island Line would also relieve mounting pressure on North Point as a main interchange station for East Kowloon and Hong Kong Island, the expert said.
A planner familiar with the Aecom Asia study said the North Island Line, passing through Central, would be the more profitable, but the Northern Link in New Territories would be the more important. 'The Northern Link is more important in terms of its strategic function, if you ask me,' the planner said. 'But of course, Chau Tau is still a rural area with few passengers, while Hong Kong Island is a prime business district.'
Apart from fares from passengers, a busy station on Hong Kong Island would yield more rental and advertising income than a station in the New Territories.
But the Northern Link would be a boon to people from Yuen Long, Tuen Mun and Tsuen Wan, who now mainly take buses and coaches to get to the Lo Wu and Lok Ma Chau checkpoints at the border with Shenzhen. The Northern Link would cut their journey times by two-thirds.
'Construction of [the Northern Link] would be easier, given that the land there is largely uninhabited,' another person involved in the study said - adding the caveat that 'obstacles may become bigger when the place is brought under development in the future'.
The North Island Line would be controversial, the person said, not only because it would play havoc with traffic during construction, but also because commuters from Hong Kong East might protest. Passengers from Tai Koo and Quarry Bay stations would no longer enjoy a direct ride to Causeway Bay and Central.
The North Island Line would connect Hong Kong station with Fortress Hill through two new stations, Tamar and Exhibition. Meanwhile, an extension from the Tseung Kwan O Line's North Point station would link it directly with Tin Hau.
The plan would give passengers from Kowloon East, including those from Tseung Kwan O and the new MTR development Lohas Park, direct access to the business centres at Admiralty and Central. But westbound passengers from Chai Wan, Tai Koo Shing and Quarry Bay would have to switch at Fortress Hill, or end up at Tamar and Hong Kong station.
'It may be a bit inconvenient for Island East commuters going to Admiralty, Causeway Bay and Central stations, but East Kowloon has a population of 300,000, while Hong Kong East has only about 200,000,' the railway expert said.
A similar reconfiguration occurred with the 2009 opening of the Kowloon Southern Link. Tsim Sha Tsui East station was removed from the East Rail Line to become part of the West Rail Line, and East Rail passengers who used to enjoy a direct ride to Tsim Sha Tsui now must change at Hung Hom.
The consultancy firm is due to submit an interim report in about a year. Officials want to hear public opinion at an early stage, as they hope to avoid the kind of controversy that ensnared the HK$66.9 billion high-speed rail link to Guangzhou.
The consultants will also be looking at the proposed Hong Kong-Shenzhen Western Express Line - which would connect Hong Kong and Shenzhen airports via Qianhai on the mainland and Hung Shiu Kiu in Hong Kong. The pace of that project, however, will depend largely on Qianhai's development.
A port rail link, which was proposed in the last railway study, in 2000, is expected to be dropped, given a decline in rail cargo business.
Time to start planning?
One expert says the Island Line, now working at about 80pc of capacity, will become saturated by: 2026