What the hell was Carlton supposed to do?

Tailgaters can fuck right off. To hell with 'em.

"Oh, oh, but he could have pulled off to the side of the road!"

Fuck off. If the guy in the BMW had stones, he could have waited until the road was clear, and passed Carlton. Last I looked, Beamers are speedy little machines, with excellent passing capabilities--especially compared to Xterras.
But he didn't. He was just trying to be a jerk.

The guy in the BMW was being an asshole, and he was the one who reduced his vision of the road, which reduced his warning lead time for roadway hazards, which in turn led to him driving over a fucking log.

Tough shit.