And for me at least, I would define railroading as the devs forcing a certain path on you, not simply encouraging you take a particular path. If we were to apply your definition, than the original Fallouts were also railroaded, since a first time player would also most likely die if they tried to deviate from the "preferred" route. But none of the obstacles to keep you on the preferred path, in the original Fallouts or New Vegas, are insurmountable - and this is what stops it from being railroading. A true railroad would be if you tried to travel north and literally could not move in that direction, due to impassable terrain or an invisible wall. Cazadores and Deathclaws, while difficult, can be avoided or possibly even killed at early levels if you have the right build.