"'[N]ot every rear-end collision is the exclusive fault of the rearmost driver. The frontmost driver also has the duty not to stop suddenly or slow down without proper signaling so as to avoid a collision'" (Martinez v Allen, 163 A.D.3d at 951-952, quoting Tutrani v County of Suffolk, 64 A.D.3d 53, 59-60; see Gomez v Pechman, 223 A.D.3d 711, 712).