I'm only familiar with HOV lanes on the far left. Check out this experiment that Detroit is trying out:
Q: How will the Detroit HOV lanes work?
A: On downtown-bound traffic on Michigan Avenue, the right lane adjacent to the parking lane -- marked with white-lined diamonds in the HOV lane -- will be reserved for vehicles with more than one person between 6 a.m. and 9 a.m. weekdays. The HOV lane is in effect on westbound Michigan from 3 p.m. to 6 p.m. weekdays.
Q: "Since the HOV lane on Michigan Avenue is also the right-turn lane, do you know ... the rule for getting into the lane to make a right turn?" asks reader Jo Vizzaccaro of Livonia.
A: Sgt. Lance Cook of the State Police said the law allows drivers who need to make a right turn or other quick use of the HOV lane to do so for only a "reasonable distance."
"That term throws the door open for interpretation," Cook said.
Ultimately, the interpretation is up to police and judges for drivers who get a ticket. Driving in the lane for a mile definitely wouldn't be considered reasonable or advisable. What might be? A half mile? A quarter mile? It's not clear under the law.
Cook's advice: "Stay out of the lane until you're ready to make a turn."
http://www.freep.com/article/20081222/COL12/812220322/0/BLOG13
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Sounds like a recipe for some very creative exit-diving if you ask me. Not to mention how hard it could be to get over to take an exit if that lane is moving significantly faster than the others.