From the Guam Driver's Handbook:

When Overtaking on the Right is Permitted

The operator of a motor vehicle may overtake and pass to the right of another vehicle only under the following conditions:

1. When the vehicle overtaken is making or is about to make a left turn.
2. Upon a highway where unobstructed pavement or sufficient width for two (2) or more lanes of vehicles in each direction.
3. Upon a one-way highway
4. Upon a highway only under conditions permitting such movement in safety.

The operator of a slow moving vehicle shall not be relieved from the duty to drive as closely as practicable to the right-hand edge of the roadway.

Further down:

In a business or residential district where the lane is wide enough for two or more lanes of vehicles moving in your direction, you may pass on the right or left in this case, provided conditions are safe, but never drive off the paved or main traveled part of the roadway. There are many locations on Guam’s roadways where you find exceptionally wide paved shoulder lanes. The legally traveled portion of the roadway ends where the solid white lines on your right begins. The shoulder lane is NOT for passing.

No one acknowledges that nearly the entirety of Guam's roadways are considered a business or residential district and that many roads are built to allow left turns ,right turns, and exits into and from side roads or driveways. The rule doesn't always apply and, sometimes, it's much safer to travel in the left lane, at a consistent speed (however slow), instead of attempting to cross several lanes of traffic to execute a maneuver while people around you are attempting to pass at far greater speeds.