Why where travelers being warned that if they rode on lusitania they would have to do so at their own risk

Because at that time, The pathway to Lusittiana was a territory conquered by the Germans troop during their conflict with Great Britain in World War I.The Germans give the warning following the international law of warfare  at that time that indicates each nations should give warning to normal civilians if they intended to target a certain area.

Due to the german subs that patrol the water it was a very high risk of it being destroyed thinking it was delivering supplies

An informal structure in a bureaucracy would be something like so-called "office politics". where there's a formal structure set up for the organization, but then an informal subculture as well that has a way of organizing the bureaucracy further. this can be positive because it sets up an added degree of organization, albeit informal, within the bureaucracy.

Abarrier that transport