Whenever any roadway has been divided into two or more clearly marked lanes for traffic the following rules in addition to all others consistent herewith shall apply:

A. a vehicle shall be driven as nearly as practicable entirely within a single lane and shall not be moved from such lane until the driver has first ascertained that such movement can be made with safety;

B. upon a roadway which is divided into three lanes a vehicle shall not be driven in the center lane except when overtaking a [and] passing another vehicle where the roadway is clearly visible and such center lane is clear of traffic within a safe distance, or in preparation for a left turn or where such center lane is at the time allocated exclusively to traffic moving in the direction the vehicle is proceeding and is signposted to given [give] notice of such allocation; and

C. official signs may be erected directing slow-moving traffic to use a designated lane or designating those lanes to be used by traffic moving in a particular direction regardless of the center of the roadway and drivers of vehicles shall obey the directions of every such sign.