What that particular RCW doesn't call out is that is illegal to pass on the right in WA except under specific circumstances. If I remember correctly generally you are only allowed to pass on the right when a vehicle is in a defined turn lane or in a carpool lane. The other acceptation, in WA, is you are allowed to pass a vehicle waiting to make a left turn on the right if you can safely do so without leaving the pavement. Visitors to the state will notice a large percentage of WA drivers will swing to the right before making a left to prevent you from going around them and if you do still have room to pass on the right if you hit the gravel shoulder you can be sited for it.