(2) Upon all roadways having two or more lanes for traffic moving in the same direction, all vehicles shall be driven in the right-hand lane then available for traffic, except (a) when overtaking and passing another vehicle proceeding in the same direction, (b) when traveling at a speed greater than the traffic flow, (c) when moving left to allow traffic to merge, or (d) when preparing for a left turn at an intersection, exit, or into a private road or driveway when such left turn is legally permitted. On any such roadway, a vehicle or combination over ten thousand pounds shall be driven only in the right-hand lane except under the conditions enumerated in (a) through (d) of this subsection.