State Route 237
Southbay Freeway
SR 237 highlighted in red
Route information
Maintained by Caltrans
Length	11 mi[1] (18 km)
Existed	1934–June 30, 1964 (as SR 9) 1964 renumbering–present
Major junctions
West end	SR 82 in Mountain View
Major intersections	SR 85 in Mountain View US 101 in Sunnyvale I-880 in Milpitas
East end	I-680 in Milpitas
Location
Country	United States
State	California
Counties	Santa Clara
Highway system
State highways in California Interstate US State Scenic History Pre‑1964 Unconstructed Deleted Freeways
← SR 236 → I-238

State Route 237 (SR 237) is a state highway in the U.S. state of California that runs from El Camino Real (SR 82) in Mountain View to Interstate 680 in Milpitas. Known as the Southbay Freeway for most of its length, SR 237 runs south of the San Francisco Bay, connecting the East Bay to the Peninsula.

Route 237 begins at a junction of Grant Road with El Camino Real (SR 82) in Mountain View, as a four lane divided highway. Most traffic comes from California State Route 85. Westbound traffic can connect to Route 85 southbound, but the eastbound traffic connection to Route 85 northbound is labeled as an exit for U.S. 101. Route 237 intersects with Highway 101 at the southern corner of Moffett Field. After this intersection, a carpool lane is added, for a total of three lanes in either direction. It remains like this until the east end of the freeway at Interstate 880, where most eastbound traffic is directed to northbound I-880. The route then becomes a city street (an arterial road), Calaveras Boulevard, in Milpitas, terminating at Interstate 680.

Starting from half a mile after the highway's western terminus, and ending at the I-880 intersection, Route 237 is named the Southbay Freeway. It is mostly constructed to Interstate standards, although there are no current plans to make it an Interstate highway.

Route 237 is known for a number of companies that define Silicon Valley's technological landscape. Many major software and hardware manufacturers have their headquarters along 237. Some of these manufacturers include Lockheed-Martin, Brocade Communications Systems, Nortel Networks, Cisco Systems, Yahoo!, Juniper Networks, TiVo, Ariba and NetApp.

SR 237 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.^[4]

The Highway 237 Bikeway is a 5-mile (8.0 km) pedestrian and bicycle path that parallels State Route 237. The majority of the path is separated from vehicular traffic, however, two sections comprising a total of 1.5 miles (2.4 km) follow an on-street alignment adjacent the freeway.

This bikeway serves as an important connector in the network of trails in San Jose and Santa Clara County. It intersects with the Guadalupe River Trail, which provides access to Downtown San Jose. It also connects to the Bay Trail, the San Tomas Aquino Creek Trail, and the Coyote Creek Trail.^[5]

The SR 237 Express Lanes, the 5-mile-long (8.0 km) high-occupancy toll (HOT) lanes along Route 237 in both directions between Mathilda Avenue in Sunnyvale and I-880 in Milpitas, opened on March 20, 2012, east of North First Street and on November 22, 2019, up to Mathilda Avenue.^[6] Instead of terminating exactly at the I-880 interchange, the Express Lanes continue along an connector ramp to I-880, so that eastbound Express Lane users merge directly into the I-880 northbound HOV lane (which itself becomes an Express Lane), and I-880 southbound Express Lane users can directly enter Route 237's westbound Express Lane.

As of August 2020, the HOT lanes' hours of operation is weekdays between 5:00 am and 8:00 pm. Solo drivers are tolled using a congestion pricing system based on the real-time levels of traffic. Two-person carpools and clean air vehicles with a solo driver are charged 50 percent of the posted toll. Carpools with 3 or more people and motorcycles are not charged.^[7] All tolls are collected using an open road tolling system, and therefore there are no toll booths to receive cash. Each vehicle is required to carry either a FasTrak Flex or CAV (Clean Air Vehicle) transponder, with its switch set to indicate the number of the vehicle's occupants (1, 2, or 3 or more). Solo drivers may also use the FasTrak standard tag without the switch.^[7] Drivers without any FasTrak tag will be assessed a toll violation regardless of whether they qualified for free.^[8]

Before Route 237 was upgraded to freeway status in 1994–1995, it was a four-lane expressway with at-grade intersections, known as Alviso-Milpitas Road or Milpitas-Alviso Road depending on different maps showing the description.

The Route 237 corridor has long been sought as a location for a freeway connector between Interstates 680 and 880. Many possible sites have been suggested, from Montague Expressway in North San Jose to Mission Boulevard in Fremont. One map printed before Route 237's construction to freeway standards between Alviso and 880 showed a new freeway across bay wetlands between Alviso and the Scott Creek Road interchange in South Fremont. Grading and underpasses for a freeway interchange are presently visible along 680 near Scott Creek Road. [1]

Except where prefixed with a letter, postmiles were measured on the road as it was in 1964, based on the alignment that existed at the time, and do not necessarily reflect current mileage. R reflects a realignment in the route since then, M indicates a second realignment, L refers to an overlap due to a correction or change, and T indicates postmiles classified as temporary (for a full list of prefixes, see California postmile § Official postmile definitions).^[9] Segments that remain unconstructed or have been relinquished to local control may be omitted. The entire route is in Santa Clara County.

Location	Postmile [9][1][10]	Exit [11]	Destinations	Notes
Mountain View	R0.00		Grant Road	Continuation beyond SR 82
	R0.00	1A	SR 82 (El Camino Real) – Mountain View, Los Altos	Western terminus of SR 237
	​	West end of freeway
	R0.38	1A	SR 85 north to US 101 north – San Francisco	Eastbound exit and westbound entrance; SR 85 south exit 22A
	R0.38	1B	SR 85 south to SR 82 south – Los Gatos, Santa Cruz	Westbound exit and eastbound entrance; SR 85 north exit 22C
	R0.61	1B	Dana Street	Signed as exit 1C westbound
	M1.55	2	Middlefield Road, Maude Avenue
Sunnyvale	2.48	3A	US 101 south (Bayshore Freeway) – San Jose	Eastbound exit and westbound entrance; westbound access is via exit 3B; US 101 north exit 396C
	2.48	3A	US 101 north (Bayshore Freeway) – San Francisco	Westbound exit and eastbound entrance; eastbound access is via exit 3B; US 101 south exit 396B
	2.99	3B	Mathilda Avenue to US 101 – San Francisco, Sunnyvale	Former SR 9 south
	​	—	SR 237 Express Lanes	West end of Express Lanes
	R3.97	4	Fair Oaks Avenue	Eastbound exit and westbound entrance
	R4.60	5	Lawrence Expressway (CR G2), Caribbean Drive
Santa Clara	R5.83	6	Great America Parkway
San Jose	6.87	7	North First Street
	8.02	8	Zanker Road
	​	—	SR 237 Express Lanes	Last access point on mainline SR 237
		—	I-880 north – Oakland	Express Lanes access only; eastbound exit and westbound entrance
Milpitas	R9.13	9A	McCarthy Boulevard
	9.34	9B	I-880 south (Nimitz Freeway) – San Jose	I-880 north exit 8B, south exit 8B-C; former SR 17
	9.34	9C	I-880 north (Nimitz Freeway) – Oakland
	​	East end of freeway
	10.00	10	Main Street	Interchange; exit ramps to Main Street from both directions; former SR 238
	11.08	11A	I-680 south (Sinclair Freeway) – San Jose	Eastern terminus of SR 237; I-680 exit 8
	11.08	11B	I-680 north (Sinclair Freeway) – Sacramento
	11.08		Calaveras Boulevard	Continuation beyond I-680
	1.000 mi = 1.609 km; 1.000 km = 0.621 mi       Electronic toll collection       Incomplete access

• California Roads portal
• San Francisco Bay Area portal

• Caltrans: State Route 237 highway conditions
• Caltrans Traffic Conditions Map
• California Highway Patrol Traffic Incidents
• Bay Area FasTrak – includes toll information on the SR 237 Express Lanes and the other Bay Area toll facilities
• California Highways: SR 237
• Highway 237 / I-880 Interchange Reconstruction Project
• California @ AARoads.com - State Route 237