The route is not like a 3-digit route as there is no Interstate 38 . It is called Interstate 238 as it was a part of California State Route 238 and no numbers with `` 80 '' at the end were able to be used . Part of State Route 238 until 1983 , and still considered the same route ( part of Route 238 ) by the California Department of Transportation ( Caltrans ) , it connects Interstate 580 in Castro Valley ( where SR 238 continues south ) with Interstate 880 in San Leandro .