But why is the tunnel so big?,(reply>), +Elliott Collins That and they'll probably want a bit extra room for future expansion, so they don't have to create an entire new tunnel system when they need to run additional cables.,(reply>), +Colton Blumhagen Probably for people. Those things are going to break or need updating now and then, and spending the money to make them comfy and well lit will likely pay for itself in time and money saved during maintenance.