Interstate 380
Quentin L. Kopp Freeway
I-380 highlighted in red
Route information
Maintained by Caltrans
Length	3.3 mi[1] (5.3 km)
Existed	1964–present
NHS	Entire route
Major junctions
West end	I-280 in San Bruno
Major intersections	SR 82 in San Bruno
East end	US 101 in South San Francisco
Location
Country	United States
State	California
Counties	San Mateo
Highway system
Interstate Highway System Main Auxiliary Suffixed Business Future State highways in California Interstate US State Scenic History Pre‑1964 Unconstructed Deleted Freeways
← SR 371 → US 395

Interstate 380 (I-380) is a short 3.3-mile (5.3 km) east–west auxiliary Interstate Highway in the San Francisco Bay Area of Northern California, connecting I-280 in San Bruno to US Route 101 (US 101) near San Francisco International Airport. The highway primarily consists of only three intersections: I-280, State Route 82 (SR 82/El Camino Real), and US 101. Like the nearby I-280, I-380 never connects to I-80, its parent Interstate Highway. However, there is no rule that says that spur routes need to do so. (Similarly, the spur route I-795 branches off from I-695, a beltway around Baltimore, and is only indirectly linked to I-95.)

I-380 is officially known as the Quentin L. Kopp Freeway, named after the prominent California state senator from San Mateo County. This highway was previously named the Portola Freeway to honor the 18th-century Spanish explorer Gaspar de Portolá, whose expedition in 1769–1770 discovered the San Francisco Bay, from a viewpoint on the Sweeney Ridge located between San Bruno and Pacifica.

Route description

I-380 begins at a junction with I-280 in San Bruno. This junction was only partially built, with room to accommodate a proposed freeway extension west toward SR 1. The freeway itself lacks overhead guide signs mentioning I-380. It then travels east through the city of San Bruno, intersecting with SR 82 (El Camino Real) before reaching US 101.

At its terminus at US 101, the mainline lanes of I-380 continue to North Access Road. The ramps to and from southbound US 101 provide connections to collector–distributor roads leading directly to San Francisco International Airport, allowing traffic between the Interstate and the airport to avoid merging with the main traffic lanes of US 101.

I-380 is part of the California Freeway and Expressway System^[2] and is part of the National Highway System,^[3] a network of highways that are considered essential to the country's economy, defense, and mobility by the Federal Highway Administration (FHWA).^[4]

History

There were plans to extend I-380 west to SR 1 (Cabrillo Highway), but, due to the route's passing over the San Andreas Fault and opposition from members of the local community, this project was abandoned. The westbound lanes of I-380 branch off to the right at I-280, leaving a wide, paved space which would carry the freeway extension under I-280 toward SR 1. This space is currently often used as storage space for equipment used in highway maintenance. A pair of unused bridges crossing over the I-280 south to I-380 east offramp remain as evidence.^{[citation needed]}

Chapter 2, Article 3, Section 608 of the California Streets and Highways Code legally defines Route 380 as traveling from "Route 1 near Pacifica to Route 280 in San Bruno",^[5] and the exit numbers assigned at I-280 start at 5 instead of 1 or 0.^[6]

Exit list

Under the official exit list by Caltrans, mileage is measured from the unconstructed western terminus at SR 1 near Pacifica. It starts at the location of the SR 82 interchange, labeling the start of the I-280 ramps at that same point.^[6] The entire route is in San Mateo County.

Location	mi[6]	km	Exit[6]	Destinations	Notes
San Bruno	5.47	8.80	5A-B	I-280 (Junipero Serra Freeway) – San Francisco, San Jose	Westbound exit and eastbound entrance; signed as exits 5A (north) & left 5B (south); west end of I-380; Exits 43B northbound & 43A southbound on I-280; stack interchange with westbound part being stub road
			5C	SR 82 (El Camino Real) – San Bruno	Signed as exit 5 eastbound
	6.23– 6.37	10.03– 10.25	6	US 101 (Bayshore Freeway) – San Francisco International Airport, San Jose, San Francisco	Signed as exits 6A (south) and 6B (north) eastbound; US 101 exit 423B
South San Francisco	6.60	10.62	7	South Airport Boulevard/ North Access Road	Eastbound exit and westbound entrance
1.000 mi = 1.609 km; 1.000 km = 0.621 mi       Incomplete access