As reported, a feasibility study is being conducted on constructing a 1km undersea link, which is slightly shorter than the Causeway. The Star also cited Ismail as saying that a detailed engineering study on the tunnel would be conducted by consultants appointed by both governments.
He said both Singapore and Malaysia had yet to determine the cost of the tunnel, which would not be parallel to the Causeway.
From
Google Map, a 1km link is only possible via Punggol area, more specifically Pulau Punggol Barat(maybe that's the reason why they opened the new road 'Seletar West Link' recently, which leads directly into Pulau Punggol Barat, see
Google Map)
Not quite possible for them to construct the 3rd link from Changi to Tanjung Pengelih as the distance apart is about 6km. Take note that 2nd link is only 1.9km while Causeway is 1.056km.