In your interpretation, how do people in FNV's world travel?
In the first two West Coast Fallout games, it's fairly clear that most people travel on foot. Cargo gets shipped using pack animals and carts. Fallout 2 is a lot more muddled, there definitely are some cars around but they seem to be way too rare to really feature into most people's lives. Vertibirds also become a factor, but they seem to be even more rare and remain that way in New Vegas.
However, in FNV you get some mentions of the NCR using forced labor to restore the rail network and shipping things by train. More importantly, the environmental design features cars (mostly military trucks) and motorcycles in a way that suggests they're still being used. On the other hand, the most discussed mode of travel and shipping cargo very much remains the Brahmin caravan.
Obviously, in reality, technical limitations kept the developers from ever even considering a gameworld that featured prominent motorized travel.
In the fiction however, at least in my mind, the question of "how do these people travel large distances?" remains open. Do NCR tourists walk all the way from California to New Vegas? Do NCR soldiers march that distance?
I'm curious how you answered these questions during your first playthroughs and why.