While all states require slow vehicles to keep right, most don't have laws that enforce that unspoken rule.
Well, at least not yet.
A bill on the table in Virginia could mean a $250 fine for what the lawmaker there calls, "Left-lane cruisers."
A similar bill is making it's way through the legislature in Oregon.
Valley drivers certainly have an opinion as well.
"You throw a driver that is driving slowing in the left lane, that means all of the faster moving traffic slows down, which means the entire interstate is moving at the slowest speed possible," said a valley resident.
"The more people going slow in the left lane, the more lane changes people have to do, so that makes it dangerous for everyone else," said another valley resident.
In various online articles, traffic safety experts say there's no specific research on the danger of left-lane driving, but some Arizona drivers don't think it's a bad idea to consider some type of legislation that would ensure drivers are aware the left lane is for passing, and passing only.
"I don't know about a fine, I just think that they probably need to post signs or something or put more information out," said a resident.
Everyone seems to agree -- more information and knowledge could be key to keeping the flow of traffic moving.