Iowa, one of the few states that does not have a requirement that cyclists ride as far to the right as practicable now requires motorists to change lanes to pass.
The Iowa Attorney General has issued an opinion (binding on all county attorneys in the state, and law enforcement as well), that the Iowa Code requires vehicles passing bicyclists to give them the whole lane.
The background to this opinion...
The Iowa Code spells out what constitutes safe passing when vehicles on public roads pass other vehicles (321.299). Although most people believe that a bicycle is a vehicle, in Iowa this is not the case. Anything that is human-powered cannot, by the definitions in the Iowa Code, be a vehicle. Bicycles are defined as 'devices'. Because of that definition (321.1, 40c), some county attorneys have concluded that bicycles are not vehicles, and therefore, the vehicles that pass them do not have to conform to the Code, which says that when passing you have to give the vehicle you're passing the whole lane (that's obvious for a car passing a car or truck, but it's also what's required when a car passes a motorcycle). Based on this interpretation, in some counties a vehicle can pass close to a bicycle and not be cited.
That interpretation is now invalid. The State Attorney has ruled that because bicyclists have "all the rights and duties...applicable to the driver of a vehicle..." (321.213, 2), then the rules of 321 apply to them as well, which includes the rule of passing and giving the device/vehicle being passed the whole lane.
Mark Wyatt, Executive Director of the Iowa Bicycle Coalition, has told the Coalition's membership that county attorneys have just received a training notification regarding this opinion, and that subsequently we expect the passing law will be enforced state-wide. There is also buy-in from law enforcement.
Already, the Iowa DOT Drivers Manual has been modified to read: "Give bicycle riders the room they deserve and need for safety. When passing a bicycle rider, pass as if the cyclist were a vehicle and move into the other lane."
Many states have a 3-foot passing law. Iowa's law is now bigger than that, cyclists there have the full lane. This came about, in part, by the work of Iowa Bicycle Coalition. Consider joining: http://iowabicyclecoalition.org/
If we could move our mountains to Iowa, I might move there:)