The center lane of a three-lane or five-lane highway is used only for what?

Passing - turning left - and to commit suicide if not driven with extreme caution.

Slower moving traffic.

It is an accumulation of oil and other fluids dripping from center under vehicles, and the lighter outer parts of the lane is also scrubbed clean by the tires of the vehicles. When it first rains...

According to the Michigan "Everything A driver needs to know" guide. No.

When not being used as a reversible lane, you may pull into it in order to clear your lane of traffic when making a left-turn across opposing ttraffic.