Many years ago I witnessed something very similar. The highway had just gone from two lanes to four lanes. I was in the right lane when a guy on a motorcycle passed on the left and then pulled back into the right lane ahead of me. A very short while later one of those Oldsmobile 'land barges' did the same thing - passed me on the left and pulled back into the right lane. But he just kept accelerating and ran right into the rear of the motorcycle. He did stop and I did also. The motorcycle was still upright and wedged about a foot back into the crumpled front of the car. The cyclist thankfully was still alive - lots of road rash but still alive.
This kind of stuff just makes me sick. Another reason I don't like to drive much in the evenings and at night. Drunks can be out anytime but more likely during non-working hours I think.