I lived not too far from the shooting for more than 15 years, and I've done that merge many thousands of times. It's an area where I've seen many problem merges and road rages.
There are so many sociology aspects that go beyond the mere black/white reporting, someone could do a masters thesis on the topic.
The area has experienced very rapid growth, and you get a mix of redneck, ghetto, and suburban commuter/soccer mom, and other cultures clashing. Unfortunately, I have to admit that many to most of the times I've seen an inconsiderate driver there, it was someone of darker skin. The offenders of this type seemed to care nothing of decency and rules of the road. The guys in the BMWs and the me-first women were also big problems. They were a different type of inconsiderate--downright aggressive.
I'm not saying the victim in this case had been inconsiderate, but even if she hadn't, someone unbalanced enough to murder someone over a traffic merge might have held resentments from past encounters.
Yes, I'm throwing out a lot of speculations...and that's my point. Not that any of them are true, but that the complexities involving that area are tangled, so we can't really assume anything.
I will be following this with great interest, both for the national reaction as well as the local details.