Before you pull into the left lane, look quickly over your left shoulder, through the back side window, to make sure there is no vehicle close behind you in the left lane. Never depend on your mirrors when you prepare to change lanes. Even correctly adjusted mirrors will leave “blind spots” behind both sides of your vehicle. If a vehicle is in the blind spot, you may not see it in your mirrors. Always quickly look over your shoulder before you change lanes or pass.https://dmv.ny.gov/brochure/mv21.pdf стр. 38