PRECAST NCRETE BOX CULVERTS • Standard box sizes: 3’ x 2’ to 12’ x 12’ in 1’ span and rise increments. • Typically me in 6’ and 8’ lengths. • Custom box sizes: Nonstandard sizing is permissible and must be designed per project design specification. 2010 ADA Standards for Accessible Design 28 CFR 35.151 New []