Corridor 1

Ultimate Interstate Corridor 1
Description Ultimate Interstate 1 is an interstate highway corridor that travels up the California Coastline from Los Angeles to San Francisco. This route could also be extended northward along the Oregon and Washington coastline to Olympia, WA.
California The route would largely replace US 101 throughout most of the state. However through the bay area it would replace I-880 along the east bay and cross using the San Rafael bridge (I-580) which is where it would route back over to back to the US-101 alignment northward. See map - Calneva Region
Oregon and Washington Entering Oregon's coast from California, Interstate highway 1 generally follows along US-101 up the Oregon Coastline connecting coastal cities like Newport, Coos Bay and Astoria. Continuing northward into Washington state This route continues along to US-101 north to Aberdeen WA and then turns east along US-12 and then WA-8 terminating in Olympia at I-5. See map - Pacific NW Region
Purpose and Need Due to the high volume of truck and commercial traffic along this corridor, and to provide additional interstate access to San Francisco and cities along the coast. the interstate 1 designation is not 100% necessary for the highway to be of interstate caliber, as the US 101 highway designation is iconic. much like the US-66 designation of America's most famous highway. US-101 shares that fame and it would be a shame to see it decommissioned. the Interstate 1 designation could be merely cosigned along upgraded portions of the route, or similar to motorway designations in the UK, such as A201 (M), the section of motorway that isn't actually signed as such is given a parenthetical designation. A similar form of designation could be reserved for iconic highways such as US 101 that need to be designated as an interstate but where preservation of the historic identity of the route is paramount.
Alternate Routing If needed the interstate could also be routed along US-101 ending at I-80 in San Francisco especially if it isnt extended northward toward Washington state. Another alternative would be to create a freeway tunnel thru San Francisco to the Golden Gate Bridge instead of using the east bay route. However due to extreme opposition to any freeway through San Francisco this likely would never happen.
Auxiliary Routes US-101* (Bayshore Freeway), I-201 (San Jose), I-301 (San Jose), I-401 (San Mateo Bridge), I-501 (Grants Pass Spur to Highway 5), I-701 (Santa Cruz Spur), I-801 (North Bay), I-901 (Monterey Spur)
Notes *US-101 (aka Bayshore Freeeway) would serve as an auxiliary route for I-1 even though it isn't an interstate.

I-1 could also be designated as I-101 as well, however this interstate designation has been proposed along the east coast.