Let's hope that pensioner, Mr Edwards, has a nice new mansion, courtesy of Mr Plumb, and Mr Plumb is now broke, jobless, and homeless. What a total douchbag.
85mph in a 20 mph residential neighborhood one lane road, then fleeing. He should never drive again. 4.6 years is hardly long enough, imo, especially with the first 1.2 spent in prison, so really he's only restricted an extra 3.4 years.

Can anyone explain the purpose of forcing traffic into the opposite lane periodically?

Traffic calming. You need to slow (or stop) and prepare to give way to oncoming traffic. It's exactly like a one lane bridge, except without the bridge.

I still don't understand this traffic calming island...but even without it, this dude may have still been hit. Scary as hell.

Without it, it looks to me like it would have been worse. More directly head on with the drivers side of the 4x4, which would be moving, adding to the impact, and no steel poles absorbing some of the energy.

a guy hit and killed two people in my neighborhood and ran away from the scene; I think he ended up with 18 years which I'd guess he ends up serving half (I really don't know how that works); 10 of the years were for fleeing the scene; I would guess fleeing is pretty common; ties into flight or fight
if I remember correctly, I think he was going either 55 or 65 in a 25

I find it disgusting that maiming two people and leaving them to die (if they had survived, runners rarely check) would get 8 years and fleeing 10, but I don't doubt it.
Depends on the state, but I think convicts with good behavior do less than 1/2 in most cases. Time served is often even better for them, getting 10 days credit for every 4 served in jail awaiting and during trial. In cali, if it's non-violent and under 4 years, you might get parole instantly, our prisons are full to bursting.

Wouldn't speed bumps cause the same "traffic calming" w/o forcing you into oncoming lane?