Why do so few people talk to their fellow travellers on planes and why do some many talk to their neighbours on trains? I think it is because we view planes as mobile offices while train travel is time away from work; more like a vacation; a time to exhale and take stock; a time for diffused thought rather than focus; a time to relax.  Planes produce the opposite effect.  With no interruptions from colleagues or relatives, we pull out our computers and phones and get work done.