The decision of Malaysia and Singapore government to built undersea tunnel instead of continuing the existing plan of crooked bridge is quite a surprise. The cost of Singapore-JB undersea tunnel will be definitely higher, and it will take a lot more time to be completed compared to the earlier plan of crooked bridge.
When I was involved in the PGB-Keppel (Singapore Gas Pipeline Project) back in 2006 , the deepest seabed between two land is approximately 20 - 25m from sea water level. Therefore the underwater tunnel must be built further more from the deepest seabed . Below is an example of an undersea tunnel which had been constructed in between UK and France.
As we can see from the picture above, the undersea tunnel have to be bored further from the land to get a gentle slope for vehicles to move in.
From the picture above, let say the tunnel will be built 20m below the seabed . The following equation derived;
40 / (x + 500) = tan (0.5 deg )
[ 40 / (tan 0.5 deg) ] = x + 500
x + 500 = (40 / 0.0087) = 4597.7m
So the estimate total length required for Singapore-JB underwater tunnel project will be around 9.2 km and of course the cost of this project will exceed more than controversial RM 1.1 billion crooked bridge. I believe Malaysian government have to spend more than RM1.1 billion to built half of this tunnel . And I guess Singapore don't really mind to spend their money on this project for the sake of preserving their 'nostalgic' Causeway.