I just don't accept that in that situation "they don't know how fast we're going."

They just passed us. They know how fast they were going before they passed, and they know how much they had to accelerate to get by us.

So saying they didn't know, pardon me but that's BS. It's just like they say "they don't see us," when the truth is that (as I say so often) they don't see school buses, garbage trucks or brick buildings at T-intersections, either. It's just that when the victim is a bicyclist, "I didn't know how fast they were going" or "I didn't see them" is accepted as an excuse by law enforcement and triers of fact.