According to the New York State Department of Transportation (NYSDOT), NY 324 begins at NY 384 in eastern Niagara Falls. NY 324 heads south, overlapping with I-190 (the Niagara Section of the New York State Thruway) across the North Grand Island Bridge to Grand Island, where it leaves the expressway at exit 20. However, as signed, NY 324 begins at the north end of Grand Island, where it splits off from the Interstate Highway as Grand Island Boulevard. South of exit 20, the official and signed routings are identical.