1. The driver of a vehicle may overtake and pass upon the right of another vehicle only under the following conditions:
a. When the vehicle overtaken is making or about to make a left turn; or b. Upon a roadway with unobstructed pavement of sufficient width for two or more lines of vehicles moving lawfully in the direction being traveled by the overtaking vehicle.
2. The driver of a vehicle may overtake and pass another vehicle upon the right only under conditions permitting such movement in safety. Such movement may not be made by driving off the roadway.