Feasibility studies have officially been launched into the prospect of building a 92km rail tunnel under the Gulf of Finland, which would be the longest transport tunnel in the world. The construction would link Tallinn in Estonia with Helsinki in Finland, making the commute between the two cities considerably easier and quicker. 
The plan which has been temporarily named ‘FinEst’ would cost between an estimated ￡8bn and ￡12bn. 
Currently, the most efficient route between the two cities is a two-hour ferry commute; the tunnel would reduce this time to just 30 minutes, making the feasibility of nationals from each country working in the counterpart much easier.  
 “Helsinki and Tallinn together constitute an economic area of busy freight traffic and nearly 1.5 million people. A growing number of commuters and leisure travellers travel between the two cities. Last year, a record of 10 million passengers arrived at the port of Tallinn”– Helsinki–Uusimaa council statement
One study is going to approximate the potential passenger volume between the two capital cities. This will be undertaken by Denmark’s Ramboll and four Finnish consultants: employee-owned engineer Sito, transport specialist Strafica, planning analyst Urban Research and consulting engineer.
Another report is set to assess the technical and economical viability of the project, primarily the construction and maintenance costs, as well as the transport modes and the safety systems that would be required. This will be undertaken by Stockholm-based Sweco, Canadian engineer WSP and the Swiss company Amberg Engineering, which was also involved in the design of the Saint Gotthard and Brenner tunnels.
Both studies are expected to conclude this year. The business case will be studied by Helsinki city council and the technical report will be read by Finnish transport agency Liikennevirasto.

Source: GlobalConstructionReview, 2017