Louisiana Highway 18 (LA 18) is a state highway that serves Ascension, St. James, St. John the Baptist, St. Charles, and Jefferson Parishes. Called the Great River Road, it runs from west to east, parallel to the west bank of the Mississippi River, running from Donaldsonville to Gretna. It spans a total of 79.7 miles (128.3 km). In the more rural parts of LA 18's span, it is commonly referred to as River Road, but it becomes 4th Street once it enters Westwego.