The Council 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 by the state law 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 the markers, buttons or signs.
(Iowa Code § 321.311) (1999 Code, § 64.01)