northbound
Historic routing By the 1920s, a road ran south from
Martinez through
Walnut Creek,
Dublin,
Danville, and
Sunol to
Mission San Jose, where it met
Legislative Route 5 (
Mission Boulevard, signed over the years as
US 48,
US 101E,
SR 9, and now
SR 238). It was not yet
paved south of Dublin, where it crossed
Mission Pass between the
Sunol Valley and the
San Francisco Bay basin. The majority of this roadway was added to the state highway system in 1933 as portions of several routes:
Route 108 from Mission San Jose to Sunol,
Route 107 from Sunol to Walnut Creek, and
Route 75 from Walnut Creek to
Pleasant Hill. At Martinez, the Martinez–Benicia Ferry took automobiles across the
Carquinez Strait to
Benicia, where
Route 7, one of the original state highways from the 1910
bond issue, led north and northeast past
Fairfield toward
Sacramento and
Oregon. The portion north from Benicia to Fairfield became part of Route 74 in 1935, when Route 7 was realigned to the more direct
American Canyon route that is now
I-80. None of the aforementioned roads were given state sign route numbers in 1934, when that system was laid out, but, by 1937, they had been numbered SR 21. This route began at the intersection of Warm Springs Boulevard and Brown Road in Warm Springs, where Route 5 and
Route 69 (
SR 17) split, followed Route 5 along
Mission Boulevard to Mission San Jose (this part later became a
concurrency with
SR 9), and then continued to
US 40 (Route 7) at Cordelia. The routing was very close to the present I-680, following such roads as Pleasanton Sunol Road, San Ramon Valley Boulevard, Danville Boulevard, Main Street in Walnut Creek, Contra Costa Boulevard, and Pacheco Boulevard. The portion of SR 21 between Pleasant Hill and Martinez was finally added to the state highway system in 1949, as a branch of Route 75. The ferry approach in Benicia became a spur of Route 74 in 1947, and, in 1953, it was transferred to Route 75. The same law, effective immediately as an urgency measure, authorized the
Department of Public Works to acquire the ferry system, then operated by the city of Martinez, which was planning to shut it down. Ownership was transferred just after midnight on October 6, 1953.
History as an Interstate . These early plans essentially called for an Interstate loop route that would head south down the San Francisco Peninsula from San Francisco to San Jose, then head north through the eastern cities of the East Bay to
Vallejo. This route now basically comprises present-day I-280, I-680, and
I-780. The
Bureau of Public Roads approved urban routes of the
Interstate Highway System on September 15, 1955, including a loop around the
San Francisco Bay, soon numbered
I-280 and I-680. The east half (I-680) began at the interchange of
US 101 north of
Downtown San Jose and followed the
Nimitz Freeway (SR 17/Route 69, now
I-880) to the split at Warm Springs (the present location of
SR 262), SR 21 to Benicia, and Route 74 (no sign route number) to
I-80 in
Vallejo. The first piece of I-680 freeway built, other than the preexisting Nimitz Freeway, was in the late 1950s, along the
SR 24 overlap between North Main Street in
Walnut Creek and Monument Boulevard in
Pleasant Hill. A southerly extension, bypassing downtown Walnut Creek to South Main Street, opened on March 22, 1960, connecting with the SR 24 freeway to
Oakland. In the next decade, the freeway was completed from Vallejo south to
SR 238 at
Mission San Jose, and the roadway north from Benicia to Fairfield, which became the only remaining piece of SR 21, was also upgraded to freeway standards. In the
1964 state highway renumbering, the legislative designation was changed to Route 680.
SR 17 was officially moved to former Route 5 between San Jose and Warm Springs, which had not had a signed designation since the Nimitz Freeway (then I-680) was constructed, but this was instead marked as part of
SR 238 (which replaced
SR 9 north of Mission San Jose), and SR 17 remained signed along the Nimitz Freeway. This was very short-lived, as the
Bureau of Public Roads approved a shift in the south end of I-680 in October 1964. However, until I-680 was completed in the early-to-mid 1970s, Because the approximate segment from Benicia to Fairfield was completed without federal Interstate funding when it was still SR 21, it is designated as a "non-chargable", Interstate. ==Exit list==