"Are you suggesting that it is impossible to ..." No, merely expensive. The Gotthard Base Tunnel is US$10.3 billion for "a route length of 57 km (35.4 mi) and

"Are you suggesting that it is impossible to ..." No, merely expensive. The Gotthard Base Tunnel is US$10.3 billion for "a route length of 57 km (35.4 mi) and a total of 151.84 km (94.3 mi) of tunnels, shafts and passages". (Quoting Wikipedia.) That's $290 million/mile. The Fehmarn Belt Fixed Link is estimate to cost €4.7 billion for 17.6 km of immersed tunnel, or $480 million/mile. The boondoggle that is the Alaskan Way Viaduct replacement tunnel is in the same range. By comparison, a rural interstate road costs about $5 million/mile, or a factor of 50 cheaper.