From an Alameda-Contra Costa Transit District (AC Transit) bulletin:
Several AC Transit bus lines in Alameda will be detoured on Wednesday, July 4, between 5 a.m. and 2 p.m. for the Alameda Fourth of July Parade.
Line 20 will operate via Atlantic Avenue, Constitution Way, 8th Street, Santa Clara Avenue, Chestnut Street, Encinal Avenue, and Willow Street into Alameda South Shore Center. Also, it will run on Broadway instead of Park Street between the Alameda South Shore Center entrance and Buena Vista Avenue. Board Line 20 at the regular stops on Webster Street at Willie Stargell Avenue or to downtown Oakland at Atlantic Avenue; inside the shopping center; or at temporary stops along Constitution Way, 8th Street, and Broadway.
Line 21 will also operate on Broadway instead of Park Street. Board Line 21 at temporary stops along Broadway or inside Alameda South Shore Center.
Board Line 31 at regular stops on Pacific Avenue at 4th Street or on Webster Street at Buena Vista Avenue but not at stops between those points.
Board lines 51A and O at regular stops on Webster Street at Willie Stargell Avenue or northbound at Atlantic Avenue; Line O on Santa Clara Ave. at 9th St.; or Line 51A on Santa Clara Ave. at 8th St. (to Rockridge BART) or Caroline St. (to Fruitvale BART) but not at stops between those points. There will also be temporary stops along Constitution Way and 8th Street.