I also do a right-turn, sometimes on red, onto a shoulder where the traffic on the road is 40 - 45 MPH.
I wait for a gap, so I don't freak the on-coming motorist out due to the small reaction time. It's bad to have lateral motion in front of me (as a motorist) with little or no time to assess and react.
If it were 30 MPH, I wouldn't bother.
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Peter Wang, LCI
Houston, TX USA