Interstate 780 (I-780) is an east–west auxiliary Interstate Highway in the San Francisco Bay Area of Northern California. It runs from Curtola Parkway and Lemon Street in Vallejo to I-680 just north of the Benicia–Martinez Bridge in Benicia. It closely parallels the Carquinez Strait for its entire route. Originally, this segment was part of I-680 before that Interstate was extended and rerouted to Fairfield. The city-maintained Curtola Parkway continues west from I-80 to State Route 29 (SR 29) in Vallejo.

Quick Facts Route information, Length ...

Interstate 780
I-780 highlighted in red
Route information
Auxiliary route of I-80
Maintained by Caltrans
Length	6.5 mi[1] (10.5 km)
Existed	1973-1976–present
History	State highway in 1935; Interstate (as I-680) in 1955; renumbered I-780 in 1973–76
NHS	Entire route
Major junctions
West end	Curtola Pkwy & Lemon St in Vallejo
Major intersections	I-80 in Vallejo
East end	I-680 in Benicia
Location
Country	United States
State	California
Counties	Solano
Highway system
Interstate Highway System Main Auxiliary Suffixed Business Future State highways in California Interstate US State Scenic History Pre‑1964 Unconstructed Deleted Freeways
← I-710 → I-805

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The I-780 state-maintained freeway begins at Lemon Street and Curtola Parkway, quickly crossing underneath I-80 at a cloverleaf interchange. The freeway passes through parts of unincorporated Solano County, then heads southeast along the Benicia State Recreation Area (a marsh). It then bypasses downtown Benicia through the hills to the north. I-780 ends at I-680 at the north end of the Benicia–Martinez Bridge, with I-680 heading south through the East Bay to San Jose.^[2]

I-780 is part of the California Freeway and Expressway System^[3] and, as with every Interstate Highway, is part of the National Highway System,^[4] a network of highways that are considered essential to the country's economy, defense, and mobility by the Federal Highway Administration (FHWA).^[5]

By 1914, a paved county road connected Vallejo and Benicia north of the Carquinez Strait,^[6] following the present Maine Street, Benicia Road, Columbus Parkway, and K Street.^[7] Although state highways were designated to Benicia in 1910 (Legislative Route (LRN) 7, now I-680) and Vallejo in 1931 (LRN 74, now SR 29), this connection was not added until 1935, when LRN 74 (an unsigned designation) was extended east from Vallejo to Benicia and north along former LRN 7 to Fairfield.^[8] (A short spur connecting Vallejo to the Carquinez Bridge was added to LRN 74 in 1937.^[9]) LRN 74 initially entered Benicia on K Street and left on East 5th Street, making several turns in between.^[7][10] Two realignments were built in the 1940s, reducing the number of turns to one, at the corner of L and East 2nd streets.^[11][12]

On September 15, 1955, the Bureau of Public Roads approved the Interstate Highway System spurs and connections in urban areas. Among these was a loop around the San Francisco Bay, soon numbered I-280 and I-680. The east half (I-680) incorporated a number of existing legislative routes, including LRN 69, LRN 108, LRN 107, LRN 75, and LRN 74, crossing the Carquinez Strait on the proposed Benicia–Martinez Bridge and ending at I-80 near downtown Vallejo.^[13][14] The first piece of this freeway north of the Carquinez Strait was at the I-80 cloverleaf interchange, built in the late 1950s when I-80 was upgraded through Vallejo. This was an extremely short roadway, beginning at Lemon Street, crossing under I-80 and Laurel Street and ending at Reis Avenue and Cedar Street.^[15][16] In about 1960, it was extended east to the old highway (Columbus Parkway) between the cities and was completed to the new bridge in about 1962, the year the bridge opened.^[15]

In the 1964 state highway renumbering, the legislative designation of the completed Vallejo–Benicia freeway was changed from LRN 74 to LRN 680, reflecting its Interstate designation. The short piece of nonfreeway in Vallejo, extending west from I-80 to SR 29, became State Route 141 (SR 141).^[17] This route followed Benicia Road and Maine Street, the same alignment the state highway had always taken; it initially connected with I-780 via Lemon Street^[18] but later followed Benicia Road from I-80 north of I-780. In 1975, a proposed (and never constructed) extension west and north to SR 37 east of the Napa River was added to LRN 141.^[19][20] The route was to be the Waterfront Freeway, scaled down to a boulevard in 1974.^[21][22]

The FHWA approved a relocation of I-680 onto the SR 21 freeway between Benicia and Fairfield in July 1973. To keep the route to Vallejo in the Interstate system, it was renumbered I-780;^[14] the corresponding legislative changes were made in 1976.^[23] As part of the project to construct a new northbound Benicia–Martinez Bridge, the I-680/I-780 interchange was rebuilt;^[when?] the new span opened in August 2007.^[24] LRN 141 was deleted from the state highway system in 1988,^[25] soon after the city of Vallejo constructed Curtola Parkway over (replacing Maryland Street) just to the south, directly connecting I-780 with a surface road to SR 29.^[11]

Mileage was measured from east-to-west based on the alignment of LRN 680 as it existed at that time. Exit numbers were still assigned the conventional west-to-east ascension.^[26] The entire route is in Solano County.

More information Location, mi ...

Location	mi[26][27]	km	Exit[26]	Destinations	Notes
Vallejo	6.75	10.86	—	Curtola Parkway – Vallejo	Continuation beyond Lemon Street
				Lemon Street	At-grade intersection
	6.70	10.78	1	I-80 – Sacramento, San Francisco	Signed as exits 1A (west) and 1B (east); west end of I-780; I-80 exit 30A
	6.58	10.59	1C	Laurel Street	Westbound signage
				Cedar Street	Eastbound signage
	5.51	8.87	1D	Glen Cove Road
Benicia	4.28	6.89	3A	Columbus Parkway	Serves Benicia State Recreation Area
	3.51	5.65	3B	Military West
	3.32	5.34	4	Southampton Road
	1.52	2.45	5	East Second Street – Central Benicia
	1.09	1.75	6	East Fifth Street
	0.00	0.00	7	I-680 – Fairfield, Sacramento, Martinez, San Jose	Eastbound exit and westbound entrance; signed as exits 7A (north) and 7B (south); east end of I-780; I-680 exit 58A northbound, 58 southbound; tri-stack interchange
1.000 mi = 1.609 km; 1.000 km = 0.621 mi

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