Gatwick bridge
Skipness, it was Almost certainly cheaper, although not cheap, to build a bridge as against a tunnel, with all the underground service issues that would entail. Any civil engineers reading will no doubt be able to quantify. Similar situation at MAN T2 where a tunnel was in the original plan for Phase 2 to link the main terminal with a proposed remote satellite servicing the 80-84 and 233-243 stands. Tunnel route still safeguarded but unlikely to be built in the foreseeable. The Gatwick idea is innovative and may be copied at MAN. These days retail rules, and remote satellites only get built if there is space to stuff them with shops and sufficient dwell time for pax to spend!