Brigde to Sri Lanka would be a nice thing and could be called modern day Ram Setu. Not the techology but high cost is the biggest impediment. This bridge could be a reality if the following developments happen:
(1) Interest and commitment from Indian as well as Srilankan Govts as well as their relationship(friendship)
(2) India & Srilanka go for many agreements and decide to increase their bilateral trade to higher levels.
(3)...
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This bridge could serve well by facilitating with cost effective movement of export-import goods between the 2 countries.
(4) Presently many large size tankers/cargo ships call at Colombo port where from the goods bound to India are transshipped to smaller ships which finally unload at Indian ports. Finally goods reach destination by road/rail. The India Srilanka Bridge could offer direct rail route from Colombo port to Indian cities.
(5) This bridge would be favourable for India's new found ambition to rise higher as a big regional power at Asian as well as a Global level.