The driver of a vehicle intending to turn at an intersection shall do so as follows:
(Code of Iowa, Sec. 321.311)
1. Both the approach for a right turn and a right turn shall be made as close as practical to the right-hand curb or edge of the roadway.
2. Approach for a left turn shall be made in that portion of the right half of the roadway nearest the centerline thereof and after entering the intersection the left turn shall be made so as to depart from the intersection to the right of the centerline of the roadway being entered.
3. Approach for a left turn from a two-way street into a one-way street shall be made in that portion of the right half of the roadway nearest the centerline thereof and by passing to the right of such centerline where it enters the intersection. A left turn from a one-way street into a two-way street shall be made by passing to the right of the centerline of the street being entered upon leaving the intersection.
The law enforcement officer may cause markers, buttons or signs to be placed within or adjacent to intersections and thereby require and direct, as traffic conditions require, that a different course from that specified above be traveled by vehicles turning at intersections, and when markers, buttons or signs are so placed, no driver of a vehicle shall turn a vehicle at an intersection other than as directed and required by such markers, buttons or signs.