Sec. 648.

(1) The driver of a vehicle or bicycle upon a highway, before stopping or turning from a direct line, shall first see that the stopping or turning can be made in safety and shall give a signal as required in this section.

(2) A signal required in this section shall be given either by means of the hand and arm in the manner specified in this section, or by a mechanical or electrical signal device which conveys an intelligible signal or warning to other highway traffic, except as otherwise provided in subsection (3). When a signal is given by means of the hand and arm, the driver shall indicate his or her intention to stop or turn by extending his hand and arm from and beyond the left side of the vehicle and signal as follows:

(a) Left turn ..... hand and arm extended horizontally.

(b) Right turn ..... hand and arm extended upward.

(c) Stop or decrease speed ..... hand and arm extended downward.

(3) A commercial motor vehicle, other than those in transit from a manufacturer to a dealer, in use on a highway shall be equipped with, and required signal shall be given by, a signal lamp or mechanical signal device when the distance from the center of the top of the steering post to the left outside limit of the body, cab, or load of the commercial motor vehicle exceeds 24 inches, or when the distance from the center of the top of the steering post to the rear limit of the body or load of the commercial vehicle exceeds 14 feet. The measurement from steering post to rear limit shall apply to a single vehicle or combination of vehicles.

(4) A person who violates this section is responsible for a civil infraction.