(a) The driver of a vehicle may overtake and pass upon the right of another vehicle only under the following conditions:

(1) When the vehicle overtaken is making or about to make a left turn; or

(2) Upon a street or highway with unobstructed pavement of sufficient width for two or more lanes of moving vehicles in the direction being traveled by the overtaking vehicle.

(b) If otherwise authorized, the driver of a vehicle may overtake and pass another vehicle upon the right only under conditions permitting such movement in safety. Such movement shall not be made by driving off the roadway.