I don’t know how many hours they have been driving.  But they are human, and not equipped to drive the inter-dimensional bus without it taking a toll.

There was a time when people could travel freely from dimension to dimension.  This idea that the universe should be broken into different dimensions is somewhat new.  It was born of fear of people different from us.  Barriers between dimensions were put in place to keep the bad people out.  But, look inside this bus.  All of us travelers sit together as we go to work or home.

That’s not exclusive to humans.  All species are capable of greed and hate, but also of compassion and love.