Thinking a bit more about the ending and series as a whole, I wonder whether Lynch intended the worlds and personas that Cooper inhabits to mimic quantum physics, given his fascination with electricity and nuclear reactions. An electron inhabits an area based on probabilities defined by a wave function equation. We only know its definite location once we stop and make an observation that collapses the equation. Interesting, it is the act of making an observation that creates the reality of the electron. Similarly, Lynchian characters, specifically in TP, are perpetually in a transition state when they are on the road. Whether it's with driving a car or a motorcycle, the true destination or intention of a character is not fully known until they stop and are observed by the audience. We also see it in Lost Highway, Wild at Heart, and even Blue Velvet. Maybe I'm overanalyzing, but Cooper at the end of E18 appears to be in a confusing superposition state 'lost between two worlds", and brings Laura along for the ride as well once her reality finally collapses.