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California State Route 120 Freeway; a surprising legacy of US 99W, US 48 and US 50

This past month I drove the entirety of the California State Route 120 freeway from west CA 99 to I-5.


The route of the CA 120 freeway has historic connections to US Route 99W when it ran between Manteca and Stockton.  US 99W was routed on what was Legislative Route Number 5 south of Stockton and LRN 66 east from Lantrop to Manteca.  LRN 66 later would be incorporated into the routing of CA 120 on Yosemite Avenue.  LRN 66 between modern day I-5 and CA 99 was part of a 1921 Legislative route adoption according to CAhighways.org.

CAhighways.org on CA 120


Originally US 99 had an elongated alignment south of Stockton.  US 99 southbound entered Stockton on Wilson Way where turned west on Charter Way and south on McKinley Avenue.  US 99 continued south to French Camp via El Dorado Road and onto French Camp Road where it met US 48 at Harlan Road.  US 99 continued southeast on French Camp Road to Main Street in Manteca.  This alignment appears to have been in use until 1929 according to USends.com.

USends.com on US 48 (i)

Likely starting in 1929 US 99 split into US 99E at Mariposa Road/LRN 4 and US 99W at Charter Way/LRN 5.  US 99E largely followed the current freeway south to Manteca.  US 99W followed McKinley Avenue, El Dorado Street and French Camp Road south to French Camp.  From French Camp US 99W continued south to Lanthrop on Harlan Road and Manthey Road where it met the new terminus with US 48. At Yosemite Avenue/LRN 66 the route of US 99W turned eastward towards US 99E in Manteca.  The split in US 99W and US 99E in Stockton can be observed on the 1930 State Highway Map.

1930 State Highway Map

1930 State Highway Map City Insert

With the above said, there is some evidence to suggest that the split in US 99W and US 99E began in 1928.  The new route of LRN 4 on Mariposa Road is shown on the 1928 State Highway Map while the former alignment on French Camp Road no longer appears.

1928 State Highway Map

CAhighways.org states that by 1935 US 50 was extended from Sacramento to Hayward.  On the 1934 State Highway Map City insert for the San Francisco Bay Area US 50 is shown ending at US 101E in Hayward.  However on the overall 1934 State Highway Map US 48 is still shown present.  State Highway Maps however don't show US 50 extended to the Bay Area until the 1936-37 edition.  Whenever US 50 was extended it was multiplexed US 99 from Sacramento to Stockton where the former took over the routing of US 99W and US 48.  Yosemite Avenue became part of CA 120 when the Signed State Routes were created in 1934.  The changes described above can be observed by comparing the State Highway Maps from 1934 through 1938. 

CAhighways.org on US 50

1934 State Highway Map 

1934 State Highway Map City Insert

1936 State Highway Map 

By the 1967 State Highway Map the planned route of the CA 120 freeway appears between CA 99 and US 50.  It isn't clear but it appears the CA 120 freeway may have been planned as part of I-205.

1967 State Highway Map

CA 120 appears as an expressway grade between CA 99 and I-5 south of Yosemite Avenue on the 1981 State Highway Map.

1981 State Highway Map

According to CAhighways (on the above CA 120 page) the route of CA 120 between CA 99 west to I-5 was fully upgraded to freeway standards by 1995.

My approach to the CA 120 freeway west was from CA 99 north.  At the junction of CA 99 and CA 120 traffic headed to Yosemite is directed to head to CA 120 east.  Traffic onto the CA 120 freeway westbound crosses over CA 99 on a flyover ramp.









The first three exits on the CA 120 freeway westbound are in Manteca.  Exit 5 accesses Main Street in Manteca.




Exit 4 on CA 120 westbound accesses Union Road.


Exit 3 on CA 120 westbound accesses Airport Way.


At Exit 1C the route of CA 120 westbound intersects it's former surface alignment and former US 99W at Yosemite Avenue.



CA 120 westbound meets the junction with I-5 at the border of Lantrop.  Northbound I-5 traffic exits right on a ramp whereas I-5 south traffic continues on an underpass.




The underpass occupied by CA 120 and I-5 was where US 99W would have met the second terminus of US 48 at Manthey Road/Yosemite Avenue.


As CA 120 west merges into I-5 in crosses over the San Joaquin River on the 1949 Mossdale Highway Bridge.  The 1949 Mossdale Highway Bridge was part of US 50, the original crossing used by US 48 was slightly upstream to the left in the photo below.


As CA 120 west ends the speed limit kicks up to 70 MPH.



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