It's several years since I've driven in the US but I seem to recall that when a police vehicle is parked as above, traffic is required to move across one lane to provide a buffer zone.
Memory is a bit hazy but I remember driving in fairly heavy traffic when everyone moved across as we passed a stationary police vehicle on the hard shoulder.
I think I was on I-25 southbound in either WY or CO.
Possibly State rather than Federal rules?
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