I can't be sure of the actual physical longest driving journey I've made. My family were fond of motoring about places and often great distances were involved.
The longest feeling one was the time my sister and I drove from Alta Loma to Castro Valley. We'd two choices: the PCH and the 5. Since the 5 was the shortest distance between the two points, we chose it over the 101 (where all of the interesting things can be found and seen).
It started off well enough, really. We thought of topics for natter, moved along at a fair clip, and then everything got yellow. The local flora took on this shade of interminable ochre that seemed to cover everything: the side of the road, the foothills, the sky at the horizon, and soon enough it got into our brains. There was nothing to break up the monotony - and then? Traffic ground to a dead halt. In the middle of the back of beyond. With no apparent cause. Simply stopped.
We'd thought to save time by going up the 5, but a journey that should have taken us round six hours (surely less than seven) took closer to eight and a half. Had we opted for the 101? It still would have taken us a year and a half, but at least we could have seen people attempting to hunt for whales from their cars - or whatsoever it is that people are thought to be doing.
Somewhere, I've got video I shot through the window when the scenery was still novel. Now, I never want to see that particular yellow again.