At the bottom of the hill I had to slam on the brakes.

The SUV I narrowly missed crashing into was too big for me to see what had stopped it, but a few seconds after, its driver pulled out and sped ahead. I remained, abreast with the cars in the other 3 lanes, at a full stop. I saw a big rig pulled off to the right, looking not-all-there and when I looked left I saw that it had dropped a whole axle mechanism. The wheels were still attached, and the whole assembly was rolling, slolwy but politely, across all four lanes. When it had crossed I-80 completely unharmed, it considerately settled in the ditch, next to the rig.

It looked like this, but with a bigger axle and 4 wheels.