The "Move Over law" varies by state, but generally requires you vacate the adjacent lane (the one you're currently traveling in), or slow down. Some states have specific speed requirements; others require only "safe and prudent" speed.
The sort of parked vehicles that require you to "move over" also vary by state. It would be "safe and prudent" to move over for <em>any</em> vehicle parked on the shoulder, especially if there are people or animals around those vehicles.
