True. the tunnel itself is the easy part. Finding the money to build it probably less so. Building the railroad lines to access it will be far the most difficult. The Sieberial side terrain may be more difficult than the Alaskan side. Much of the approach is quite mountainous. On the US side getting past the EPA would literally require an act of Congress. Can anybody say "Pristine Wilderness"?
Therer was an article published in the December 1994 Bulletin of the American Railway Engineering Association (Bulletin No. 748, Vol. 95) n the subject of the tunnel.
Title: Interhemispheric Bering Strait Tunnel & Railroad. Author: G. Koummal. A few points from it:
The idea was first proposed in 1849.
The maximum depth of the strait is 174 feet.
The presence of Little Diomede Island (US) and Big Diomede Island (Russia) makes the project two end to end tunnels.
The shoreline to shoreline distances are US side to LD Island: 36.25 km and Russia side to BD Island 36.4 km.
He was proposing one single track tunnel for trains and a parallel service tunnel with these located so that a second tunnel could be drilled later when traffic required.