A proposal for a road-rail tunnel across Qiongzhou Strait linking Guangdong and Hainan provinces has been submitted to China’s top economic planning agency, the National Development and Reform Commission, for approval after 20 years of research, reports China Ocean News.

The road-rail tunnel would help with the further development of links between the economies of the two provinces, and also ease traffic congestion during peak seasons such as the summer holiday and Spring Festival. And the road-rail tunnel will incorporate Hainan province into China’s road and railway system: At present, travelers to Hainan have to travel by plane or ferry.

More than two decades and $12 million have been spent researching the geography of the Qiongzhou Strait since China’s Ministry of Transport first assigned the project to the Guangdong government in 1994. It is reported that some $20 billion would need to be invested into the tunnel program to make it a reality.