What the duck?

So about a week ago I noticed a duck laying dead on the side of the freeway. Unusual roadkill I thought, since whenever I see ducks they're either flying way above car level, or when they're on the ground it's next to, if not reasonably close to some sort of water source. But this was on the 91 freeway, about ten miles east of the 5. And unlike a crow or a turkey vulture or something, it's not like a duck would wander onto the road to get at a piece of food or something. So it struck me as being strange, but I didn't think much about it.
That is, not until early Sunday morning as I'm driving down the road and the car in front of me brakes suddenly and comes almost to a stop before finally veering to the left to reveal a male mallard. Yes, the same kind of duck I saw taking a nap on the shoulder of the 91 a few days earlier. So I took my turn passing the duck, making sure I was clear of him, but couldn't help cutting it really close, just to try to scare him out of the road. But the bird seemed completely oblivious to the cars speeding by it. Either oblivious or indifferent. But either way, that's weird, right?