What does a blinking left arrow mean?

A blinking left arrow is used when a left turn is permitted, but oncoming traffic still has a green light and turning vehicles must yield the right of way to any oncoming vehicles.

Signal phases

Source: MDOT

Resources

MDOT explains flashing yellow left-turn signal
YouTube

Flashing Yellow Arrow Left-Turn Signal webpage
Michigan DOT

MUTCD Section 4D.04 Meaning of Vehicular Signal Indications

E. Flashing yellow signal indications shall have the following meanings:

Vehicular traffic, on an approach to an intersection, facing a flashing YELLOW ARROW signal indication, displayed alone or in combination with another signal indication, is permitted to cautiously enter the intersection only to make the movement indicated by such arrow, or other such movement as is permitted by other signal indications displayed at the same time.

Such vehicular traffic, including vehicles turning right or left or making a U-turn, shall yield the right-of-way to:

(a) Pedestrians lawfully within an associated crosswalk, and

(b) Other vehicles lawfully within the intersection.

In addition, vehicular traffic turning left or making a U-turn to the left shall yield the right-of-way to other vehicles approaching from the opposite direction so closely as to constitute an immediate hazard during the time when such turning vehicle is moving across or within the intersection.
FHWA

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This work by the Cornell Local Roads Program (CLRP) is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported License.