I'm in a lot of stop and go traffic in the morning (and evening) too on the freeway. My drive is quite long (35 miles one way) and during the first 10-12 miles I'm moving at a steady pace. However, I've noticed with the shorter days, that when I use the headlights they seem fine for a while, then during the stop and go portion (which is about another 12 miles) my headlights will dim for a brief moment just once then go back to normal.

Is the electrical system resetting somehow? Is this normal?

I had to replace the battery recently due to a cracked casing and thought this would go away if the battery was somehow being the culprit. But no change. Otherwise the car runs fine.