Interstate 238 and California State Route 238

Interstate 238 and State Route 238
Interstate 238 and State Route 238
	I-238 highlighted in red; SR 238 in purple; the gap represents the relinquished portion
Route information
	Maintained by Caltrans
Length	11.20 mi (18.02 km) Portions of SR 238 have been relinquished to or are otherwise maintained by local or other governments, and are not included in the length.
History	Designated 1934 (as SR 9); July 1, 1964 renumbered SR 238; Northernmost portion designated I-238 in May 1983 by FHWA
Component; highways	SR 238 from Fremont to Castro Valley; I-238 from Castro Valley to San Leandro;
Major junctions
South end	I-680 in Fremont
	SR 84 in Fremont; SR 92 / SR 185 in Hayward; I-580 in Castro Valley;
North end	I-880 in San Leandro
Location
Country	United States
State	California
Counties	Alameda
Highway system
	Interstate Highway System; Main; Auxiliary; Suffixed; Business; Future; State highways in California; Interstate; US; State; Scenic; History; Pre‑1964; Unconstructed; Deleted; Freeways;

Route 238, consisting of State Route 238 (SR 238) and Interstate 238 (I-238), is a mostly north–south state and auxiliary Interstate highway in the San Francisco Bay Area of California. The southern segment is signed as SR 238 and is a divided multilane surface highway that runs parallel to the Hayward hills between I-680 in Fremont and I-580 in Castro Valley. The northern segment is signed as I-238 and is a six-lane freeway that runs more east–west between I-580 and I-880 in San Leandro.

The numbering of I-238 does not fit within the usual conventions of existing three-digit auxiliary Interstate Highways, where a single digit is prefixed to the two-digit number of its parent Interstate Highway as I-38 does not exist. The I-238 number was specifically requested by the state of California so it could match the California Streets and Highways Code and because all three-digit combinations of I-80 (the primary two-digit Interstate in the Bay Area) were already being used in the state.

Though some maps and signs mark SR 238 as continuous through Hayward, control of most of the route within the city was relinquished to that local jurisdiction and is thus no longer officially part of the state highway system.