(1) Upon all unlaned streets of sufficient width a vehicle shall be driven upon the right half of the street except:
(a) When lawfully overtaking and passing another vehicle proceeding in the same direction.
(b) When the right half of a roadway is closed to traffic while under construction or repair.
(c) Upon a roadway designated and sight posted by the municipality for one-way traffic.
(2) All vehicles proceeding at less than the normal speed of traffic at the time and place and under the conditions then existing shall be driven as close as practicable to the right hand curb or edge of the roadway, except when overtaking and passing another vehicle proceeding the in the same direction or when preparing for a left turn.