Can someone explain the move over law?

http://www.ontario.ca/fr/lois/loi/90h08#s159s1

I totally understand the reasoning for proceeding safely around emergency vehicles and tow trucks, but this law seems incredibly vague. I actually don't know how to be compliant in some situations.

If traffic is jammed (likely due to the accident they're responding to), do you have to get into the other lane? Like if you're doing 5km/h in the lane next to them because it's bumper to bumper do you have to come to a stop if there's nowhere to merge, or can you proceed slowly by? How slow is slow enough for other situations? The US laws are mostly "posted speed minus 20 mph" which seems more reasonable and enforceable.

If you come up to a cop and traffic is moving at 120, then you drop down to 80 and pull in front of the other cars, that seems far worse than if you just stayed in your lane and reduced your speed.