California Highways (www.cahighways.org): Route 24

Post 1964 Signage History

▸In 1963, there was an additional segment before this one: "Route 17 near Castro Street in Oakland to Route 580". In 1981, Chapter 292 deleted this segment, moving that routing to I-980. That segment was originally LRN 226, defined in 1959.

▸This segment (former (b), now (a)) remains as defined in 1963.

In 1966, construction was completed on Route 24 (Grove-Shafter Freeway) between 0.4 mi W of Route 13 in Oakland and the Caldecott Tunnel in Berkeley (1.3 mi).
(Source: CHPW Nov/Dec 1966)

The Gateway Boulevard viaduct on Route 24 west of Orinda may have been constructed for the intersection of a future freeway, according to one account that I read. I have not yet confirmed this. The viaduct is located near where Route 93 was planned to intersect Route 24.
(Source: Mail from Jason A. Bezis, 7/2/2002)

Pre 1964 Signage History

State Shield In 1931, a routing from a proposed Oakland tunnel to Walnut Creek was proposed. This appears to correspond to the eventual Route 24, however, this segment was not included in the original signage of Sign Route 24 defined in 1934.

1955 Rte 24 California Highways and Public Works, in April 1931, reported that Joint Highway District Number 13, composed of Alameda and Contra Costa counties, had organized for construction of a public highway and tunnel to supersede the pre-1931 narrow, crooked and inadequate 'Tunnel road in Alameda County and to improve the Contra Costa County road from the tunnel to the town of Walnut Creek. The state proposed for inclusion as a state highway that portion of the route in Contra Costa County between. the tunnel and Walnut Creek, a distance of 9.6 miles. Based on the volume and class of traffic on the pre-1931 tunnel road and on the other highways leading into Oakland (one from Livermore via Hayward, the other from Martinez through Crockett), and estimating the effect of better facilities in the Walnut Creek area, the conservative 12 hour traffic was anticipated for 1940 as equivalent to a 24 hour traffic of 17K vehicles on Sundays and 10K on weekdays. The state felt this route qualified for state inclusion based on volume, importance, and character of 1931 and future traffic.

In October 1935, it was reported that the Sign Route 24 signage had been extended south from Sacramento to Oakland, via Isleton, Antioch, and Walnut Creek. This may have been related to the opening of the Broadway Tunnels. Note that portions of what was Sign Route 24 are present-day Route 242 and Route 4.

Sign Route 24 started at US 40 (now I-80) at the Oakland City Hall at 14^th and San Pablo. It then ran along Broadway to College, then along College to Claremont Ave. Along Claremont, it entered Berkeley. It jogged briefly along Ashby Avenue (present-day Route 13, LRN 206, defined in 1935) to Tunnel Road, continuing into Contra Costa County. The route was LRN 75.
(Source: Old Oakland Maps, 1936)

Sign Route 24 then ran E to Walnut Creek (along present-day Route 24); this was LRN 75. It was then likely cosigned with Sign Route 21 until the Sign Route 21/Sign Route 24 junction (this segment of Sign Route 21 was also LRN 75). This was all defined in the 1931-1933 time, but was not signed as Sign Route 24 in 1934.

The original routing for Route 24 included what is now Route 13 (renumbered in 1964) between the present Route 13/Route 24 interchange in Oakland and I-80. That segment was LRN 206, and ran along Ashby Avenue. It was added to the state highway system in 1935. However, the actual highway did not exist until the Broadway (later called "Caldecott") Tunnel opened in 1937.

The Ashby routing was part of the larger Bay Bridge project which included construction of the Eastshore Highway with which Ashby connected. On the other side of the hills, Route 24 was routed on Mount Diablo Boulevard.

Caldecott Tunnels and Predecessors

The original routing between Oakland and Lafayette over the Berkeley Hills of Alameda County followed a steep ascent via what is now Telegraph Avenue and Claremont Avenue. Upon cresting the Berkley Hills this road would have followed what is now Fish Ranch Road in Contra Costa County. The first known concept for a tunnel through the Berkeley Hills emerged in 1860 but was rejected by the populace in Alameda County and Contra Costa County. Another concept emerged in 1871 as an extension of Broadway via a vaguely described path which would emerge somewhere near San Pablo Creek in Contra Costa County. This 1871 concept would eventually emerge as the route of a choice for a tunnel and would sporadically be under construction during the following decades. Eventually the tunnel construction was taken up by the Merchants Exchange of Oakland which procured the funding and permits to complete construction.
(Source: Gribblenation Blog (Tom Fearer), “Former California State Route 24 through the Kennedy Tunnel and Old Tunnel Road”, January 2021)

Routing of the original Kennedy Tunnel The resulting "Inter County Tunnel" was opened November 4th, 1903, and was later renamed as the "Kennedy Tunnel". It was a single-lane, timber-supported, 1000' structure that served as a conduit until 1937, when the first Caldecott bores were completed and dedicated. The tunnel closed in the 1940s. Lafayette residents protested the tunnel, predicting that it would increase competition for land and price them out of the market. But private and county money eventually financed a tunnel. The Kennedy Tunnel had a four-foot elbow in the middle; diggers had miscalculated the meet-up. The tunnel was also called the the Broadway Tunnel (although that name was also used for the Caldecott, at one time). The western entrance was near Tunnel Road and Skyline Boulevard. The eastern entrance is at the end of Old Tunnel Road. At the east entrance, a residence owned by the East Bay Regional Park District stands on the former site of the Canary Cottage cafe. The original tunnel has been abandoned and the ends sealed.
(Image source: December 1937 CHPW)

Broadway was chosen for LRN 75 (Route 24) over versus Ashby Avenue (LRN 206 / Route 13) as Broadway, at the time, connected directly with Tunnel Road whereas Ashby Avenue did not yet connect.
(Source: Gribblenation Blog (Tom Fearer), “Former California State Route 24 through the Kennedy Tunnel and Old Tunnel Road”, January 2021)

In 1937, the Caldecott Tunnels (called the Broadway Low-Level Tunnels) opened, a twin-bore tunnel designed to replace the dark, dank, single-bore Kennedy Tunnel 300 feet above it. At that time, some 30,000 cars were passing through Kennedy every week. The twin tunnels, each 3000' feet, were concrete lined, lighted, and had forced air ventilation. Note that as the two tunnels were curved at the end and joined one another at a single portal building at each end, there was a belief that there was just a single tunnel with a thin concrete supporting wall. In reality, the roadways are 150' apart except at the two ends. Each of the tunnels has a 22' wide roadway and a with of 26' 8" between the sidewalls. Each bore carried one direction of traffic.

Development in Contra Costa boomed and a third bore opened in 1964, outfitted with a system of tubes that popped out of the pavement and allowed workers to change directions of the middle bore to handle traffic, which generally flowed west in the morning and east in the evening. Modern standards required that the highways at each end of the tunnels be widened and straightened and that the third bore be made wider than the first two. As the third tunnel was to be considerably larger than the two older tunnels, it was not possible to adapt the original plans to the new location. The third tunnel has a 28 foot wide roadway and is 34 feet 6 inches wide between the sidewalk. The vertical clearance is 17 feet above the pavement, compared with the 14 feet 10 inches in the two older bores. In addition to the larger size of the tunnel itself, there are numerous other features which are new or improved. The entire length of the roadway is illuminated by a continuous line of fluorescent lights on each side of the ceiling. Extra lights are placed for a distance of 300 feet at each end so that there is a gradual transition in the daytime in order to allow drivers' eyes to adjust to the change from the bright sunlight outside and the artificial light in the center of the tunnel. Emergency power facilities have also been installed for use in the event that there is a power loss from the serving utilities. A new transverse system of ventilation is being used. Fresh air is taken in at the westerly portal building and carried along a duct above the roadway. It is discharged into the roadway section through openings at one side of the ceiling. The fresh air mixes with exhaust fumes from the vehicles, and is drawn out through exhaust ports on the opposite side of the ceiling, then carried to the westerly portal building and discharged straight up into the atmosphere. The two fresh air and two exhaust blowers have a capacity of a half-million cubic feet of air per minute. On October 6, 1964, dignitaries from throughout the area assembled to dedicate Tunnel III to the name and further honor of Thomas E. Caldecott.

Caldecott Tunnel Medallions Adorning the original Caldecott Tunnel bores are medallions that were designed by Henry Meyers, the official Alameda County architect in the 1930s. One depicts people facing each other to symbolize how the tunnel joins the residents of Contra Costa and Alameda counties; another shows a car headlight exiting a tunnel. Meyers may have had a lot of help from draftsman George Klinkhardt in designing the tunnel exterior and medallions, a Caltrans report suggests. In fact, Klinkhardt may have designed the entire tunnel exterior, the reports says. Meyers, who grew up in Livermore and whose Alameda home has been turned into a museum, designed more than 200 buildings, including Highland Hospital in Oakland, the Posey Tube in Alameda and 10 veterans memorial buildings, including the ones in Livermore and Pleasanton. In 2012, Caltrans held a student design competition to design medallions to adorn the new 4th bore. The competition will be limited to students from Contra Costa and Alameda counties. The six new hexagon-shaped medallions -- each about 36 inches high -- will be public art for the ages.

In July 2012, the updated artwork was chosen. Specifically, six students’ winning images of Mount Diablo, rugged foothills, and the sun will be built into the exterior of the Caldecott Tunnel Fourth Bore.

Status

This route is constructed as a freeway.

Caldecott Tunnel Rehabilitation (04-Ala-24, PM R5.80/R6.24; 04-Cc-24, PM R0.00/R0.60)

The 2022 SHOPP included the following new project: 04-CC-24 R0.01. PPNO 0480B; ProjID 0414000011; EA 0J540. Route 24 In Orinda, at the Caldecott Tunnel № 28-0015R, 28-0015, and 28-0015L. Rehabilitate Caldecott Tunnel Bores 1, 2, and 3. Total Project Cost: $69,487K. Begin Con: 10/1/2026.
(Source: “2022 State Highway Operation And Protection Program, Fiscal Years 2022-23 through 2025-26”, March 17, 2022)

In August 2025, the CTC approved for future consideration of funding 04-Ala-24, PM R5.80/R6.24; 04-Cc-24, PM R0.00/R0.60. Caldecott Tunnel Bores 1, 2, and 3 Rehabilitation and Ventilation Upgrade Project. Rehabilitate Bores 1, 2, and 3 of the Caldecott Tunnel at PM R5.80/R6.24 and R0.00/R0.60 on Route 24 in Alameda and Contra Costa Counties. This project will preserve the structural integrity of the tunnel and extend its service life. (PPNO 04-0480B) The project will install a new fire suppression and ventilation system. The project is currently programmed in the 2024 SHOPP. The total programmed amount which includes Right of Way (Support and Capital), and Construction (Support and Capital) is $242,608,000. Construction will begin in 2026-27. The scope, as described for the preferred alternative, is consistent with the project scope as programmed by the Commission in the 2024 SHOPP. The project will result in less than significant impacts to the environment after mitigation. Project implementation may have significant impacts on cultural resources, specifically, the bores as historical resources. However, mitigation measures will reduce any potential impacts on the environment to less than significant. These measures include, but are not limited to, preparation of a Built Environment Treatment Plan, maintaining Historic American Engineering Record documentation, developing webinar and virtual tour materials and conducting a limited number of in-person tours of Bores 1 and 2, and installation of interpretive panels that discuss the history of the tunnels. As a result, an MND was completed for this project.
(Source: August 2025 CTC Agenda, Agenda Item 2.2c.(1) #2)

In August 2025, the CTC approved the following pre-construction phase allocation for a 2024 SHOPP SB1 project: $14,584,000. ~~04-CC-24 R0.01~~ 04-Ala-24 R5.8/R6.2. PPNO 04-0480B; ProjID 0414000011; EA 0J540. Route 24 In Orinda, at the Caldecott Tunnel № 28-0015R, 28-0015, and 28-0015L~~. Rehabilitate Caldecott Tunnel Bores 1, 2, and 3.~~; also in Contra Costa at Caldecott Tunnel (R0.0/R0.6). Rehabilitate and upgrade ventilation system of Caldecott Tunnel Bores 1, 2, and 3. (G13 Contingency) Concurrent consideration of funding under Resolution E-25-48; August 2025. Pre-Construction Phase Allocation: Budgeted (Actual, if different): PS&E $14,400,000; RW Sup $184,000.
(Source: August 2025 CTC Agenda, Agenda Item 2.5b.(2b) #3)

In June 2026, the CTC amended the following project that currently in the 2026 SHOPP: 04-Ala-24 R~~5.8~~5.7/R6.2. PPNO 04-0480B; ProjID 0414000011; EA 0J540. In Orinda, at the Caldecott Tunnel № 28-0015R, 28 -0015, and 28-0015L; also in Contra Costa at Caldecott Tunnel (R0.0/R~~0.6~~0.7). Rehabilitate and upgrade ventilation system of Caldecott Tunnel Bores 1, 2, and 3. This is a Construction Manager/General Contractor (CMGC) project. Note: Increase in construction capital to add underdrain system upgrades in Bores 1 to 3. ~~Split electronic communication integration work into project EA 0J541/PPNO 04-3924W from parent project EA 0J540/PPNO 04 0480B.~~ Adjust postmiles at starting and ending project limits for traffic switching and traffic control work during extended tunnel closure. Update description to show CMGC delivery method. Allocation changes ($ × $1000): PA&ED $6,269; PS&E $14,400; R/W Sup $184; Con Sup $20,850; R/W Cap $253; Const Cap ~~$200,652~~ $203,402; TOTAL ~~$242,608~~ $245,358.
(Source: June 2026 CTC Agenda, Agenda Item 2.1a.(1d) #13)

4^th Bore - Caldecott Tunnel (~ ALA R5.858 to CC R0.416)

TCRP 15 In September 2000, the California Transportation Commission considered (TCRP Project #15) a $15 million allocation for phase one of construction of a fourth bore tunnel with additional lanes for the Caldecott Tunnel (~ ALA R5.858 to CC R0.416). The total estimated cost is $185 million. This project was requested by the Metropolitan Transportation Commission. Bore 3, constructed in the early 1960's (long after bores 1 and 2) was actually constructed with the fourth bore being kept in mind. As evidenced by the tunnel, stub lanes (on both ends of the tunnel) do actually indicate a 4^th bore was in mind, as small strips of pavement (wide enough for 2 lanes) spur from the existing highway before fading off into the bushes and trees before entering the tunnel. This is currently planned to complete construction in late 2012. Funding was extended for this in September 2005.

The SAFETEA-LU act, enacted in August 2005 as the reauthorization of TEA-21, provided the following expenditures on or near this route:

High Priority Project #2369: Construct fourth bore of Caldecott Tunnel on Route 24, California. $1,600,000.

In February 2006, the CTC noted that the goal of TCRP Project #15 is to improve the movement of people and goods along Route 24 via the Caldecott Tunnels, to improve travel time and therefore reduce delays, and enhance safety of the traveling public and Department maintenance workers. When the environmental process started, seven alternatives were under consideration. Based on several screening criteria, four alternatives were dropped. The elimination of the four alternatives reduced the cost and the Department and the Contra Costa Transportation Authority (CCTA) have identified $5,000,000 of available TCRP funds for other work. In February 2006, the Department and CCTA request that the funds be redistributed to Plans, Specifications, and Estimates. The Draft Environmental Document is being finalized and will be ready for circulation in July 2006. The alternatives being considered are:

Two-lane tunnel north of the existing bores (Alternative 2N). Alternative 2N would include the construction of a new tunnel with two westbound through lanes and one standard and one non-standard shoulder on an alignment north of the existing tunnels.
Three-lane tunnel north of the existing bores (Alternative 3N). Alternative 3N would include the construction of a new tunnel with three westbound through lanes and standard shoulders on an alignment north of the existing tunnels.
No- Build Alternative.

The Final EIR was received in December 2007, and the CTC indicated construction is estimated to begin in Fiscal Year 2009-10. The total estimated project cost, capital and support, is $420,000,000. The project is funded from $175,000,000 local funds, $20,000,000 Traffic Congestion Relief Program funds, $1,000,000 Federal Demonstration funds, $18,000,000 in Regional Improvement Program funds, $31,000,000 Interregional Improvement Program funds, and $175,000,000 Corridor Mobility Improvement Account funds. The funding sources were adjusted in June 2008.

In January 2009, Caltrans removed one of the last obstacles preventing it from adding a fourth bore to the Caldecott Tunnel by settling a lawsuit with Oakland residents concerned about the impacts of building the new tunnel. The settlement to the suit by the Caldecott Fourth Bore Coalition calls for Caltrans to:

Build $2 million in improvements to Route 13 - Tunnel Road - in Berkeley. They would include additional traffic signals, signal coordination, and projects to improve safety and access for bicyclists and pedestrians.
Conduct a $250,000 study of Route 24 that would consider charging tolls or using carpool lanes and examine ways to boost transit ridership, increase the bicycle capacity aboard BART trains, and encourage bike and pedestrian use.
Monitor and control noise, light, dust and traffic impacts from the tunnel construction.
Extend the lease of Frog Park, beneath Route 24 at Claremont Avenue, and make improvements to the park.

The settlement was crafted between attorneys for the coalition and Caltrans with pressure from state legislative leaders and Gov. Arnold Schwarzenegger, who wanted to see the fourth bore built as part of his state economic stimulus strategy. He had sought to have the project exempted from the environmental review process, which would have nullified the suit, but that undoubtedly entangled the project in other legal challenges. However, the project may still get caught up in the 2008/2009 Budget mess. The $420 million Caldecott Tunnel project depends on $194.5 million from the transportation infrastructure bonds voters approved in 2006. Plans to hire a contractor to start digging the long-awaited fourth bore this summer were halted Jan. 14 2009, when the California Transportation Commission froze funding for the Caldecott Tunnel and 26 other projects that had been scheduled to receive $293.5 million in state funding. If the governor and the Legislature settle the budget crisis by early February, the fourth bore could receive funding from the transportation commission on Feb. 18 and Caltrans could start the process of hiring a contractor by March 1 - just two to four weeks behind schedule.

At the January 2009 meeting, the CTC deferred to February (and in February, deferred it to March... and in March, to April) discussion about reorganization of this project. The intent is to split the original project into four segments, as follows:

Segment 1 — Construct 2-lane fourth bore (PPNO 0057A).
Segment 2 — Realign westbound Route 24 to northbound Route 13 (0057G).
Segment 3 — Improvements to Kay Street Overcrossing (0057I).
Segment 4 — Highway planting (0057J).

The basic plans for the project are:

Construct a 2-lane fourth bore for the Caldecott Tunnel, north of the existing third bore.
Modify two interchanges and one intersection.
Construct retaining and soundwalls.
Construct tunnel cross passages.
Demolish the existing operations and maintenance control (OMC) building.
Construct a new OMC building.

In April 2009, the CTC approved funding this project (as a loan against future bonds) from 2009 Stimulus funds. It was advertised for construction in May 2009.

In late January 2010, politicians and transportation officials gathered in an enclosed and heated tent in Orinda, not far from the tunnel, to celebrate the official groundbreaking for the $420 million fourth bore. After an hour and a half of speeches, they grabbed gold-painted shovels and dug from a pile of dirt trucked in for the ceremony. Actual construction was already under way with contractors clearing brush and preparing to erect retaining walls on both sides of the tunnel and a sound wall on the west end. In June 2010, workers expect to begin digging the new tunnel from both ends. Tunneling crews will dig the new hole in the Oakland hills in segments, first digging out the top of the tunnel, then building the tunnel gradually by excavating a segment and bolstering it with braces and sprayed concrete. They will also dig seven cross-passages to the third bore - to provide emergency exits. The completed bore will be 41 feet, 3 inches wide and 3,389 feet long. Caltrans officials expect the project to create about 5,000 jobs during the four years of construction. Nearly half of the money to pay for the project is coming from federal stimulus funds. John Porcari, deputy secretary of the U.S. Department of Transportation, said the fourth bore is the largest recipient of stimulus funds for infrastructure in the nation.
(Source: "Work begins on Caldecott Tunnel's 4th bore", San Francisco Chronicle, 1/23/2010)

Before the actual tunnel construction starts in July 2010, there has been significant preparatory work. Since January 2010, construction crews have been busy building retaining walls to keep the hills from collapsing onto Route 24. To build the retaining walls, crews are boring holes about 2 1/2 feet across, 8 feet apart and 36 feet to 97 feet deep. The bottoms of the holes are filled with concrete, then steel I-beams are dropped in. When all the beams are in place, the dirt in front of them will be removed and wooden planks will be inserted between the beams to hold back the hillside. Eventually they'll be covered in concrete. The crews are also constructing and portal walls that will form the eastern and western entrances to the new two-lane fourth bore. Just north of the existing westbound tunnel, workers are preparing the concrete and steel faces through which the digging of the fourth bore will commence. The face is a series of interlocking columns formed by boring holes, filling them with concrete, then boring new holes in between, and filling them with concrete. The walls are then tied together and strengthened with steel, creating a strong surface to dig through. Walls on each side of the face are built by covering the soil with concrete then inserting long, thick steel reinforcement rods into the earth. They're grouted in place and act like long, strong nails. Workers have also constructed a $3.5 million charcoal gray temporary sound wall between the freeway and the apartments and condos on Caldecott Lane, just west of the tunnel. This wall was constructed by putting I-beams in the ground, putting huge wooden planks between them, then fastening 2-inch-thick noise-absorbent plastic pads on both sides. The walls sport slanted tops pointed toward the freeway. The idea is to trap the noise, light and dust generated during construction when trucks use the narrow strip between the freeway and the wall as a staging ground with a concrete plant, water-treatment facility and dumping area for soils excavated from the Oakland hills. Additionally, trees have been removed from the hillsides, a traffic signal is being installed on Upper Broadway, and three electrical substations are under construction.
(Source: "Caldecott Tunnel fourth bore under construction", San Francisco Chronicle, 5/21/2010)

In his 2006 Strategic Growth Plan, Governor Schwartzenegger proposed completing the Caldecott Tunnel Corridor. In 2007, the CTC recommended using $175M from the Corridor Mobility Improvement Account (CMIA) for the 4th bore.

In July 2010, it was reported that The $420 million excavation of a fourth bore of the Caldecott Tunnel between Orinda and Oakland has opened a door for paleontologists to search for fossils expected to give clues to old life-forms and climate change in the Bay Area. Private paleontologists hired by Caltrans already have found a tooth — likely a remnant of a camel — and dozens of remains of fish scales, plants and other bone bits in dirt and rock dug up, shoved around and shored up in early construction work outside the new bore site. One area considered prime for fossil finds is the Orinda Formation, a jumble of fractured layers of old stream beds and flood plains. The silt and sediment there is ideal for covering up and preserving fossils from creatures that roamed the East Bay 9 million to 10 million years ago in the Miocene period. This is the first time that Caltrans has called in paleontologists to a Bay Area freeway project at its beginning to monitor for fossils. Caltrans said it is paying about $35,000 a month for the paleontological work. The duration of the collection will be shaped by how long the crews keep finding fossils.

In March 2011, it was noted that, after a year of construction, construction crews have dug out more than 900 feet -- or 27 percent -- of the 3,389-foot-long Caldecott Tunnel fourth bore, a project now estimated to cost $391 million after favorable construction bids lowered the cost from $420 million. The 21,665 cubic meters of earth and rock excavated from the Caldecott fourth bore so far would cover a football field 16 feet deep. When the project is finished, the excavated earth would cover a football field 134 feet deep.

In September 2011, the New York Times reported on this construction. It noted that the project was projected to create 4,500 jobs. The work in the tunnel is more dangerous than work in the average tunnel. Safety regulators declared it “gassy” from the start because of the naturally occurring methane gas in the guts of the Berkeley Hills. Anything that could spark an explosion, from cellphones to lighters, is banned from the inside of the tunnel. Because of sections of precariously weak rock, miners must use what is called the New Austrian Tunneling Method, meaning that crews dig just short distances before taking measures to reinforce the tunnel. The digging machine, called a roadheader, is a 130-ton instrument that looks like a metal brontosaurus with a spiked metal rotating head for grinding rock. It is followed by a remote-controlled robot on wheels that sprays a special quick-drying concrete over the newly bored section. With another machine, the miners then drive long steel dowels into the tunnel walls to reinforce them before proceeding. Once the boring is completed, it will take two more years to scoop out the bottom portion, install ventilation, lighting and communication systems, and otherwise transform the rough-hewn hole through the hills into a subterranean stretch of freeway. By the end of 2013, the tunnel be able to accommodate four lanes of traffic in each direction. It will eliminate the need for Caltrans workers to engage in an often futile game of trying to minimize backups by switching the direction of traffic through the center bore at least twice daily, often more frequently.

In November 2011, it was reported that construction of the fourth bore broke through the Orinda hillside, thus connecting the two sections of the tunnel being dug. In January 2012, it was reported that state safety regulators have ruled the fourth bore project is no longer classified as a "gassy" tunnel, where methane and other gases could trigger explosions or fires.

In March 2012, it was reported that a competition was being held to design adornments for the 4th bore. Caltrans announced in late March 2012 the opening of the unusual competition to design six, 36-inch tall architectural medallions that will be cast out of concrete above the entrances to the Caldecott Tunnel fourth bore on Route 24. May 7 2012 was the deadline to submit original art deco drawings, which Caltrans plans to use in designing molds for pouring concrete to form the decorative shapes. The competition was limited to students from kindergarten through high school in schools in Contra Costa and Alameda counties. This is the first student-only architectural design competition Caltrans has used in the Bay Area. Caltrans picked "classic art deco" as the theme after the art style was strongly favored in an agency online poll on six different themes, and was the theme used on the other bores.

In April 2012, it was reported that excavation was taking longer than expected, owing to tough digging conditions. In Fall 2011, a crew of miners and their brontosaurus-like digging machine encountered unexpectedly difficult conditions — including harder rock formations and, in some places, water.

In August 2012, it was reported that the 4th bore was completed. This bore contained safety features developed as a result of the crash of a drunk driver inside the Caldecott Tunnel on April 7, 1982. The crash touched off a chain reaction that turned the third bore into a 2,000-degree tomb and killed seven people. There were no emergency passages, and the narrow tunnel had no shoulder. There were no traffic lights, emergency gates or message signs to warn motorists of the fireball inside, caused when a gasoline tanker burst into flames. Utilizing lessons leared from this accident, new safety features for the third and fourth bores include traffic lights and a traffic gate that swings down in emergencies. The third and fourth bores also will be the first to have an extensive network of electronic message signs and traffic signals inside; and unlike the original two bores, the third and fourth will be connected by seven lighted, 12-foot-wide escape passages. The escape passages are air pressurized to keep smoke and toxic gases away from fleeing travelers. Additionally, only the fourth bore has a shoulder, a 10-foot wide swath to stash damaged vehicles or for fire trucks, ambulances or law enforcement to access accidents. The Caldecott Tunnel also is safer than it was in 1982 because of a ban on trucking gasoline and other flammable liquids or poison gases through the tunnel, except between 3 and 5 a.m. Even when the new bore opens, some safety features will be hidden, such as water lines. Some will be too small to see, like heat sensors. Most obvious will be 19 ceiling-mounted fans, all capable of churning up 20 mph breezes to sweep away smoke and gases. The fans are more powerful than those in the other bores. One new safety feature common to all four bores is a radio override system that allows tunnel operators to broadcast emergency messages on car radios, regardless of the station to which they are tuned.
(Source: Contra Costa Times, 10/31/13)

In November 16, 2013, the new fourth bore opened.

Naming

Route 24 from I-580 to the Caldecott Tunnel (~ALA R1.914 to ALA R5.837) is named the "William Byron Rumford Freeway". Byron Rumford was a State legislator. Named by Assembly Concurrent Resolution 137, Chapter 92 in 1980. The dedication plaque reads: William Byron Rumford Freeway, Member of the California Legislature 1948-1966, Community and Civic Leader. This freeway on the state system is named in honor of William Byron Rumford Sr. for his long and dedicated service to his state, community, and mankind." William Byron Rumford (February 2, 1908 – June 12, 1986) was a pharmacist, community leader, and politician. He was the first African American elected to any public office in Northern California, and the first African American hired at Highland Hospital. Rumford graduated from a segregated high school in Arizona in 1926. At 18, he moved to San Francisco and worked for a year, before attending Sacramento Junior College. The School of Pharmacy at the University of California, San Francisco accepted Rumford, and he worked his way through school, working as a parking valet and a doorman at night, and graduated in 1931. While at UCSF Rumford was a member of the Alpha Phi Alpha fraternity. At the age of 25 William Rumford passed the State of California employment examination in 1933, at a time when very few African Americans worked for the State. After passing the employment exam, Rumford took the California Board of Pharmacy investigator examination, where he twice passed the written part of the exam, but was twice failed on the oral portion. Rumford then passed the examination for California State Venereal Disease investigator, but again was failed on the oral presentation portion for a third time. Undaunted, Rumford visited one of the members of the Personnel Board who lived in Oakland. Christenson, the board member, appealed the Board's decision to fail Rumford based on the grounds that he was asked irrelevant questions. Rumford went on to appeal on the grounds that the Board had publicized statistics that African Americans suffered from sexually transmitted diseases at a greater rate than other ethnic groups, but had not taken done anything to improve the situation. Rumford won the appeal and was granted his California State certification. Rumford became co-owner of a pharmacy in Berkeley in 1942 at the age of 34, which he later purchased outright and renamed Rumford's Pharmacy. He tried to continue with his job at Highland Hospital while running the pharmacy. Eventually, Rumford decided to leave Highland Hospital, devoting his time fully to the pharmacy. In addition to his business, Rumford was director of the Red Cross Oakland chapter, President of the East Bay Health Association, and a member of the Democratic Central Committee for the Bay Area. In 1944, he was appointed by Governor Earl Warren to the Rent Control Board. He helped found the Berkeley Interracial Committee. Rumford served in the California State Assembly from 1948–1966, with a special focus on in fair employment, control of air pollution, and fair housing. In 1955, Rumford first introduced a Fair Housing Act, and in 1963, the California State Legislature passed the Rumford Fair Housing Act which outlawed restrictive covenants and the refusal to rent or sell property on the basis of race, ethnicity, gender, marital status, or physical disability.
(Bio: Oakland Wiki; Image source: Read the Plaque; Join California)

This segment is historically part of "El Camino Sierra" (Road to the Mountains). It continues along what is now I-680.

Named Structures

The “Kennedy Tunnel”, the predecessor tunnel to the Caldecott or Broadway Tunnel, was named for L. W. Kennedy. Kennedy is said to have first conceived the idea of a toll road and tunnel between the counties. He started a company which built a road and began work on a tunnel, but "Work was begun upon the hole in the hill, but a rush of water was struck to the extent that it collapsed the tunnel and the company at the same time." Note that other sources claim that Wright F. Kelsey was the first to propose building a tunnel between the counties.

The "Caldecott Tunnel" (structure 28-015) (~ ALA R5.858 to CC R0.416) on Route 24 between Alameda and Contra Costa Counties was named for Thomas Edwin Caldecott (July 27, 1878 – July 23, 1951), who was a pharmacist and politician when the tunnel was built. From 1923, Caldecott served in politics in Alameda County, California in the San Francisco Bay Area until 1951. Caldecott was born in Chester, England on July 27, 1878. Both of his parents were Welsh. The family immigrated to Toronto, Ontario, Canada about 1882. Caldecott grew up in Canada, and obtained a pharmacy degree from the University of Toronto in 1900. Thomas and his brother visited Berkeley, California, and shortly thereafter in 1903, moved their entire family there. That same year, Caldecott bought a pharmacy at Dwight Way and Shattuck Avenue, later moved to Ashby Avenue and Adeline Street in the Webb Block, a building which was designated a local landmark in 2004. Caldecott was elected to the City Council of Berkeley in 1923. In 1930, he was appointed to fill out the remaining term of Mayor Michael B. Driver. He then successfully ran for the office of Mayor in 1931, serving until December 1932. He was then elected as a supervisor on the Alameda County Board of Supervisors, serving from 1933 until his death in 1951. He was chairman of the board from 1945-1946. In 1948, he formed the Alameda County Highway Committee, "to solve sectional differences over highway problems." He was also instrumental in establishing a new Alameda County Juvenile Hall, which was completed after his death in 1951. Caldecott served as the president of Joint Highway District 13, which oversaw the construction of the multi-bore Broadway Low Level Tunnel through the Berkeley Hills east of San Francisco Bay. When opened in 1937,[14] it was the longest tunnel in the State of California, and accomplished the opening up of the entire region east of the hills as a major suburb of the Bay Area. At an event that year, Caldecott was honored "as the man responsible for the success of the project". In 1941, Caldecott was publicly commended for his "untiring efforts" in bringing the project to a successful completion. In 1960, the tunnel was re-named the "Caldecott Tunnel", in recognition of his leadership on the project. The tunnel was originally called the "Broadway Low-level" Tunnel (the former tunnel through the Oakland hills was at a much higher elevation.) It was built in 1937 and refurbished in 1965, and was named by Assembly Concurrent Resolution 8 in 1969.
(Image source: Oakland Museum; Bio information: Wikipedia)

Ellen O'Kane Tauscher The fourth bore of the Caldecott Tunnel (Route 24,~ CC R0.071) is named the Representative Ellen O’Kane Tauscher Memorial Bore. It was named in memory of Ellen O’Kane Tauscher, a dedicated public servant serving the 10th Congressional District from 1997–2009. Ellen O’Kane was born in Newark, New Jersey, in November 1951, the daughter of a grocery store owner. She earned a degree in early childhood education from Seton Hall University in 1974. In her mid-20s, she became one of the first women to hold a seat on the New York Stock Exchange, serving from 1977–79, and during her 14-year Wall Street career, she also served as an officer of the American Stock Exchange. In 1989, Ellen O’Kane married William Tauscher and raised a daughter, Katherine. The couple later divorced. In 1992, Ellen O’Kane Tauscher founded a service for preemployment screening of childcare providers. She later authored the Child Care Sourcebook. She also created the Tauscher Foundation, which donated two hundred thousand dollars ($200,000) to California and Texas schools to buy computer equipment for elementary education. Ellen O’Kane Tauscher received her first political experience serving as the state cochair for Dianne Feinstein’s successful 1992 and 1994 Senate campaigns. In 1996, Ellen O’Kane Tauscher challenged incumbent California Republican Representative William P. Baker in a newly created Delta district comprising bedroom communities that are the most conservative in the San Francisco Bay area. She ran on a platform of gun control, women’s reproductive rights, and increased spending on education, along with the reduction of wasteful fiscal spending and narrowly won, with 49 percent of the vote to Baker’s 47 percent, in a race with three minor party candidates. In the next two elections, Representative Tauscher won by slightly more comfortable margins over Republican candidates, defeating Charles Ball 53 percent to 43 percent and Claude B. Hutchinson 52 percent to 44 percent. When Representative Tauscher took her seat in the 105th Congress (1997–1999), she was assigned to three committees: National Security (later renamed Armed Services); Science, Space, and Technology; and Transportation and Infrastructure. In the 106th Congress (1999–2001), Representative Tauscher resigned her Science, Space, and Technology Committee seat to focus on her two other assignments, where she remained for the balance of her career in the House of Representatives. Representative Tauscher’s committee assignments provided her a national platform from which she also was able to serve district needs. As a member of the Armed Services Committee, she outlined an activist role for the United States in the international arena. Her district was the only one having two national defense laboratories, Lawrence Livermore and Sandia, and she secured nearly $200,000,000 in funding for Livermore’s “super laser” project. Representative Tauscher also had a prominent role as the senior Democrat on the congressional panel overseeing the National Nuclear Security Administration, which manages the United States nuclear weapons program. From her seat on the Transportation and Infrastructure Committee, Representative Tauscher steered federal funding to improve the San Francisco Bay area’s badly strained transportation systems, including $33,000,000 for projects in her district. In 1998, Time magazine dubbed her moderate Democratic approach to politics “Tauscherism,” a kind of middle-of-the-road politics that blended fiscal conservatism with social liberalism and reflected the political realities of her suburban district, which, until reapportionment in 2002, was more Republican than Democratic. When the lines were redrawn by the California Legislature, Representative Tauscher easily won reelection to a fourth term, with 75 percent of the vote against Libertarian candidate Sonia E. Harden. In 2004, Representative Tauscher won reelection with 66 percent of the vote against Republican Jeff Ketelson, and in 2006 and 2008 voters returned her to office with 66 percent and 65 percent of the vote, respectively. On May 5, 2009, Representative Tauscher was nominated by President Barack Obama to be the Under Secretary of State for Arms Control and International Security. On June 25, 2009, Representative Tauscher was confirmed to the position of Under Secretary of State by a voice vote of the United States Senate and resigned her seat in Congress the next day to take the position. Representative Tauscher represented the United States at numerous international meetings and negotiations, including setting into motion the New START Treaty, the first major nuclear arms reduction and limitation agreement with Russia in over two decades, which was signed in 2009, and ratified in 2010. Representative Tauscher served the Obama administration as Under Secretary of State until February 7, 2012, when she was named Special Envoy for Strategic Stability and Missile Defense, a position she held until August 31, 2012. In 2013, Representative Tauscher was elected chairperson of the Alliance for Bangladesh Worker Safety, a group of 28 global retailers, and led efforts that created industry safety standards in response to the fire and collapse of a Bangladeshi garment factory that killed over 1,000 workers. In March 2013, Governor Edmund G. Brown, Jr., appointed Representative Tauscher as the chair of the Governor’s Military Council and was tasked with expanding defense industry jobs and investment in California. On September 17, 2013, Representative Tauscher was named as an independent member of the Board of Governors for Lawrence Livermore National Laboratory and Los Alamos National Laboratory, and served as chair of the Board of Governors beginning on February 16, 2018. On June 2, 2017, Governor Edmund G. Brown, Jr., appointed Representative Tauscher to serve on the Board of Regents of the University of California. She passed away in 2019. Named by Senate Concurrent Resolution 77, Res. Chapter 32, 09/11/20.
(Image source: Find a Grave)

Interstate Submissions

The portion from Route 13 to Walnut Creek was submitted for inclusion in the interstate system in 1945; it was not accepted.

Scenic Route

[SHC 263.3] From the Alameda-Contra Costa county line to Route 680 in Walnut Creek.

Eligible for Scenic Highway status per [SHC 263.2]. The following portions have been officially designated as Scenic Highway and are signed:

From E PORTAL of CALDECOTT TUNNEL to I-680 near WALNUT CREEK. CC R0.3/9.1. 8.8 mi in Contra Costa County. Designation #45, October 22, 1982

Classified Landcaped Freeway

The following segments are designated as Classified Landscaped Freeway:

County	Route	Starting PM	Ending PM
Alameda	24	R1.85	R4.88
Alameda	24	R5.24	R5.89
Contra Costa	24	R0.40	R0.62
Contra Costa	24	R1.82	R2.85
Contra Costa	24	R3.29	R5.26
Contra Costa	24	R5.53	R9.14

Post 1964 Signage History

The 1964 renumbering reallocated the segments E of Pittsburgh as follows:

Route 4 (Concord to Antioch)
Route 160 (Antioch to Sacramento)
Route 16 (Sacramento to Woodland)
Route 113 (Woodland to Yuba City/Marysville)
Route 70 (Marysville to US 395 at Hallelujah Junction)

Pre 1964 Signage History

Rte 24 1934 Routing

Pre-1964 State Shield From Sign Route 4 (Route 24's present-day terminus), it continued cosigned with Sign Route 4 between from near Concord to near Antioch. This was LRN 75, defined in 1931. In 1964, this segment was renumbered as Route 4.

Pre-1964 State Shield Sign Route 24 then ran N to Sacramento, following the route of present-day Route 160, entering along Freeport Blvd. This was LRN 11, defined in 1933. It originally ran N on Freeport to Broadway.

Pre-1964 State Shield In Sacramento, Route 24 ran W along Broadway as part of LRN 50. It then ran N along 3^rd/5^th St., also as part of LRN 50 (Sign Route 16, defined in 1933). It continued N to "I" street, co-signed with Sign Route 16. This is now signed as Route 16.

Pre-1964 State Shield Prior to 1960, Sign Route 24 continued W out of the city co-signed with Sign Route 16 along LRN 50 to Woodland. Again, this is now just Route 16.

Pre-1964 State Shield In Woodland, Sign Route 24 diverged from Route 16 and continued N to Yuba City/Marysville along LRN 87. It was cosigned with US 40A, and this segment is now part of Route 113.

Pre-1964 State Shield From Woodland, Sign Route 24 ran along the route from Woodland at Jct. US 99 to Jct. Sigh Route 7 (later renumbered as US 395) near Reno Junction, via Oroville and Quincy (Reno Junction was the former name of what is now Hallelujah Junction, Reno Junction having replaced Chats). Signage as Sign Route 24 started in 1934.

US Highway Shield In 1954, Sign Route 24 was either co-signed or resigned as Alt US 40 (US 40A). The article announcing the designation indicated that existing signs would be replaced by US 40 signs with the designation "Alt". The article indicated that for the first 10 miles N, from US 40 in Solano County, the new alternate route would be designated as US 99W and US 40A. A new section of highway was being constructed to intersect with the existing US 99W at the Woodland Wye. This would be the segment that is now Route 113. In Woodland, US40A joined with the existing US 99W / Sign Route 24 to Yuba City; this is now Route 113. US 40A then followed Sign Route 24 (now Route 70) through Oroville and Quincy to US 395. Lastly, US 40A followed US 395 S to Reno, which was the eastern terminus of US 40A. The goal here was to provide an alternate route across the Sierras when Donner Pass was closed. Note that some maps from the early 1950s also show Sign Route 24 being extended from Hallelujah Jct. to the Nevada State boundary along US 395.
(Source: Roseville Press-Tribune 3/23/1954 via Joel Windmiller (email), 11/12/2023)

According to Chris Sampang and Joel Windmiller, the following are some former routings of US 40A/Route 24 between Woodland and Reno:

Oswald and South Yuba City: Oswald Road and Railroad Avenue were the original routing of Route 24, later US 40A south of Yuba City; this was bypassed in 1957.
Yuba City: Bridge Street is the former Route 20, US 99E, US 40A (and Route 24). Live Oak Boulevard from Yuba City north through Berg to Lomo (where the current Route 99 freeway ends) appears to be former US 99E continuing down Live Oak Boulevard north to Live Oak.
Laurel Lane/Chandler Road in Yuba County: This appears as an "Old State Highway" on both Mapquest and MSN Mappoint.
Oroville: The current route of Route 70 around Oroville is not the original highway—it used to enter the town, but was bypassed in the early 1960s (as US 40A) in the midst of construction of Oroville Dam.
Near Keddie, through the Mount Hough State Game Refuge: Both Mapquest and MSN Mappoint show an "Old Highway Road" from southeast of Round House Road to the edge of the Plumas National Forest; in the Plumas National Forest is the "Old Keddie Highway". This road starts and ends at Route 70/Route 89 via a circituous routing through the refuge.
East of East Quincy: MSN Mappoint and Mapquest show an "Old Highway" and "Old Highway Road" stubbing out from La Porte Road and Route 70/Route 89 going east to dead end right where Route 70/Route 89 cross a portion of the Plumas National Forest.
After crossing Greenhorn Creek, in the Plumas National Forest: Per MSN Mappoint and Mapquest, there is an "Old 402A" that takes an alternate routing around the creek. Chris surmises that this may just be a typo for "40A".
Sloat, just south of the Plumas National Forest boundary: Chris notes that there is an "Old Road" headed southbound off of Route 70/Route 89, which then reconnects to Sloat Road, which connects back to Route 70/Route 89 before the highway reenters the Plumas National Forest.
Clio to Delleker: Beginning at the Middle Fork of the Feather River west of Clio, "River Road" and "Clio State Route 40A Road" continue eastbound all the way back to Route 70 about 3 miles west of Delleker. The west end no longer connects to Route 70 or Route 89, suggesting that current Route 89 between Clio and Blairsden may have been US 40A at one time, and a connection may have previously existed over the Feather River between Graeagle and the west terminus of River Road.
Reno Junction to Border Town, NV: The former routing of US 40A (and US 395 until 1976) south of Reno Junction was Scott Road, which leads back to the current US 395 expressway just north of the Nevada Border. The current interchange of Route 70 and US 395 at Hallelujah Junction only dates back to the 1970s, when the US 395 expressway was completed; Route 70 was extended two miles east from Reno Junction on new alignment to Hallelujah.

Chris also notes that Scott Road north of Reno Junction to just south of Omira was also US 395 pre-expressway. Constantia Road between Omira and Doyle, Doyle Loop in Doyle itself, and Old Highway from Doyle to just west of Lassen County Route A26 also appear to be former alignment (Old Highway passes south of the Doyle State Wildlife Area, but the current US 395 expressway goes right through it between Laver Crossing and Lassen County Sign Route A26.)

Sign Route 24 in Sacramento

Around 1960 the routing changed to a new routing along LRN 232, which used Jiboom Street and El Centro Street. This routing used the original Jiboom Street bridge over the American River and Main Drainage Canal. The Gribblenation Blog, "Highways in and around Old Sacramento; US 40, US 99W, CA 16, CA 24, CA 70, CA 99, CA 275, and more" provides a detailed history of the various highways (US 40, US 99, Route 16, Route 24, Route 70, Route 99, Route 275, Route 51, I-5, and I-80 in the Old Sac area.

"I" Street Bridge - Sacramento

The predecessor to the I Street Bridge at the Sacramento River was constructed by the California Pacific Railroad Company. The structure was located just north of modern I Street and became functional on January 29, 1870, when the first train crossed. This structure only served trains. The Central Pacific Railroad was acquired by the Southern Pacific Railroad in 1885, but continued to operate as a leased line. The Southern Pacific Railroad, Yolo County and Sacramento County came to an agreement on construction of the I Street Bridge on February 14, 1910. The project initially faced difficulties due to the hesitancy of Yolo County due to the lack of support by the Northern Electric Railroad. The Southern Pacific eventually threatened not to construct an automotive road deck atop the structure which saw Yolo County relent. Yolo County would officially endorse construction of a road deck atop the I Street Bridge on September 8, 1910. Construction of the I Street had commenced on June 8, 1910. The structure would be completed on April 29, 1912, at a cost of approximately $1,000,000. Like the 1870-era railroad span the I Street Bridge retained a turntable swing design.
(Source: Gribblenation Blog (Tom Fearer), "I Street Bridge (former California State Route 16 the Sacramento River)", 10/24/2025)

Originally, LRN 6 used the "I" Street Bridge. The I Street Bridge opened to traffic over the Sacramento River in 1912 as a swing span. It is is owned by the Union Pacific Railroad. The top deck of this 400-foot-long structure carries automotive traffic from I Street in Sacramento to C Street in West Sacramento. The bottom deck carries the tracks of the Union Pacific Railroad. By 1917, LRN 6 departed Sacramento westward via the I Street Bridge to Washington (now West Sacramento). Prior to the construction of the Yolo Causeway, a primitive seasonal road known as "Tule Jake Road" could be utilized to traverse Yolo Basin by car between West Sacramento and Davis (seasonal, as the Yolo basin flooded six to eight months every year). After completion of the Yolo Causeway (then referred to as the Yolo Basin Trestle) between West Sacramento and Davis, LRN 6 was moved to the "M" Street Bridge, which eliminated a rail overpass from the alignment. In 1935, the "I" Street Bridge became part of LRN 50 as part of the 1935 codification of LRN 50 as "[LRN 15] to Sacramento via Rumsey and Woodland" (previously, LRN 50 had ended in Woodland); the "I" Street Bridge was then signed as part of Sign Route 16. The structure became part of Sign Route 24 when that highway was extended to Oakland in 1935.
(Source: Gribblenation Blog (Tom Fearer), "The history of Sacramento's Tower Bridge (Currently California State Route 275 and former US Routes 40/99W)", 10/8/2025;Gribblenation Blog (Tom Fearer), "I Street Bridge (former California State Route 16 the Sacramento River)", 10/24/2025)

In 1935, the Jibboom Street Overhead was announced as a recommended project. The proposed span would serve as a connection between Jibboom Street and the I Street Bridge. Concepts of the Jibboom Street Overhead noted that the project was planned as a Federal cooperative and included a replacement for the original eastern approach to the I Street Bridge. The original eastern approach landed at I Street just west of 2^nd Street. The new approach was planned to be elongated towards 3^rd Street. Jibboom Street originally connected to 2^nd Street via an at-grade crossing of the Southern Pacific Railroad. The Jibboom Street Overhead and realigned eastern approach to the I Street Bridge were dedicated by the Governor on October 1, 1937. In 1949, Legislative Chapter 1467 defined a duplicate LRN 207 as a new State Highway between Sacramento and Marysville; this highway incorporated the Jibboom Street Overhead branching north of the I Street Bridge. The corridor was originally subject to the provisions of the Collier Burns Act of 1947 regarding maintenance. The duplicate LRN 207 was renumbered as LRN 232 in 1951; the Collier Burns Act provision the highway was subject to was removed in 1955. Sign Route 24 would continue to use the I Street Bridge until it was realigned onto the Jibboom Street Bridge (LRN 232) in 1960.
(Source: Gribblenation Blog (Tom Fearer), "I Street Bridge (former California State Route 16 the Sacramento River)", 10/24/2025)

Over on AAroads, Scott Parker noted the following about the I-Street routing: The original LRN 232 (after 1958 signed as Route 24) diverged from LRN 50/Route 16 at the intersection of the I Street extension bridge immediately east of the Sacramento River swing-span (shared with UP/former SP tracks on the lower/ground level deck) and Jibboom Street (both are elevated over the RR tracks). It headed north on Jibboom over a through-truss bridge crossing the American River; the street ended at Garden Highway—atop the river levee—at which point LRN 232/Route 24 turned west. About a mile west of there, the state highway diverged from Garden Highway along a broad arc descending north from the levee onto El Centro Avenue, which it utilized north into Sutter County. LRN 232 and Route 24 terminated at LRN 3/US 99E at a diamond interchange in Olivehurst.

After 1964, Route 99 was defined as running through Sacramento and Route 70 was originally signed to terminate at Capitol Mall. Route 99 and Route 70 would initially use the eastern I Street Bridge approach to reach the Jibboom Street Overhead. These were temporary routings. In 1970, following the completion of I-5 north of downtown Sacramento during the late 1960s, both Route 99 and Route 70 were moved to I-5 and would multiplex the freeway.
(Source: Gribblenation Blog (Tom Fearer), "I Street Bridge (former California State Route 16 the Sacramento River)", 10/24/2025)

The I Street Bridge was removed as part of the State Highway System and as part of California State Route 16 in 1984.
(Source: Gribblenation Blog (Tom Fearer), "I Street Bridge (former California State Route 16 the Sacramento River)", 10/24/2025)

In October 2018, it was reported that the City of Sacramento and Caltrans have initiated a project that will replace the historic I-Street Bridge (for vehicular traffic) and the Jibboom Street approach to the bridge for a new vehicular continuation of Railyards Blvd. to C Street. The I Street Bridge is 100 years old (and is a former routing of Sign Route 16 and Sign Route 24 (as LRN 50)) and the lanes are too narrow to serve buses, there are no bicycle lanes, and sidewalks are too narrow to meet accessibility standards. The I Street Bridge and the four associated approach structures are on the eligible bridge list for federal funds for replacement and/or rehabilitation through the Highway Bridge Program (HBP). The I Street Bridge has been classified as functionally obsolete, and the existing approach structures have been classified as structurally deficient. The I Street Bridge Replacement project will include construction of a new bridge upstream of the existing I Street Bridge. The new bridge will cross the Sacramento River between the Sacramento Railyards and the West Sacramento Washington planned developments and provide a new bicycle, pedestrian, and automobile crossing. The existing I Street Bridge would continue to be used by the railroad. The approach viaducts to the existing I Street Bridge will be demolished, which should result in better access to the water front in both cities. (See Route 16 for the new routing)
(Source: City of Sacramento, I-Street Bridge Replacement)

Over on AAroads, Scott Parker (Sparker) noted the following about the I-Street routing: The original LRN 232 (after 1959 signed as Route 24) diverged from LRN 50/Route 16 at the intersection of the I Street extension bridge immediately east of the Sacramento River swing-span (shared with UP/former SP tracks on the lower/ground level deck) and Jiboom Street (both are elevated over the RR tracks). It headed north on Jiboom over a through-truss bridge crossing the American River; the street ended at Garden Highway — atop the river levee —, at which point LRN 232/Route 24 turned west. About a mile west of there, the state highway diverged from Garden Highway along a broad arc descending north from the levee onto El Centro Avenue, which it utilized north into Sutter County. LRN 232 and Route 24 terminated at LRN 3/US 99E at a diamond interchange in Olivehurst.

In November 2022, it was reported that the plan to turn the top level of the I Street Bridge into a pedestrian walkway and bike lane over the Sacramento River was progressing. In Fall 2022, project planners filed financial documents, and in late October 2022 the project was recommended for a $16 million grant through the state’s Active Transportation Program. The current bridge will be superseded by a new bridge between C Street in West Sacramento and the Railyards — a $260 million, 300-foot-long feat of architecture that will replace the I Street Bridge as the route cars take over the river. As for the old bridge, the plan is to use the 111-year-old I Street Bridge for railroad traffic, which runs on the bottom deck of the bridge. As for the top? The city of West Sacramento has spearheaded the plan to repair the bridge’s narrow sidewalk and turn the vehicle lanes into a bicycle track and walkway. The $16 million state grant still has to be formally approved by the state Transportation Commission. The Sacramento Area Council of Governments previously awarded the project $3.6 million to complete the final design and right-of-way phase. The total cost of planning and constructing the project is estimated at $22.6 million. After securing more than $19 million in outside funding, the city will pay the rest. Final planning should be complete and construction could be ready to begin in or before 2026 — but that will largely depend on the timing of the completion of the new Railyards bridge. The plan is to be ready so that as soon as the new bridge is cleared to start taking vehicle traffic, the deck conversion of the old bridge can start. The project should be finished by late 2027 or 2028.
(Source: Sacramento Business News, 11/7/2022)

In December 2022, it was reported that the CTC approved $16 million for the I Street Bridge Deck Conversion Project. This project will repurpose and modernize the historic I Street Bridge to close an active transportation gap and foster economic development between low-income and disadvantaged neighborhoods in West Sacramento and Sacramento. The project will construct and connect new Americans with Disabilities Act compliant bicycle/pedestrian ramps on both sides of the Sacramento River and enhance the upper deck to facilitate and encourage active transportation between the two cities.
(Source: Appeal Democrat, 12/9/2022)

In December 2023, it was reported that Construction on a new bridge connecting West Sacramento and the Railyards is anticipated to begin in 2025. Currently, the I Street Bridge replacement project is not fully funded, and construction will begin once all financial support is secured. So far, officials have completed the environmental documentation, and are working through the permits, right-of-way acquisition and final design. Even after construction starts it’ll be a while before the new bridge graces the city. The project will take approximately four years to construct to comply with environmental mitigation and flood control work windows. If construction begins in 2025, the new bridge would be completed by 2029. The existing I Street Bridge is more than 110 years old; the nine-foot lanes are too narrow to serve buses, there are no bicycle lanes, and the sidewalks are too narrow to meet current accessibility standards. A new bridge will be built upstream from the current one and will cross the Sacramento River, connecting the Railyards to West Sacramento’s Washington neighborhood. The current bridge will remain and serve as a railroad crossing on the lower deck, the city said, while the upper deck may be used by pedestrians and bicyclists. The new vertical lift bridge will feature 6-foot bike lanes and 12-foot shared paths for pedestrians and bicyclists. It can also withstand more than 25,000 vehicles daily, according to the city’s 2020 news release. The bridge’s contemporary blueprint is bolstered by two curved green and white pillars on each side, which light up at night.
(Source: Sacramento Bee, 12/15/2023)

In October 2025, the CTC approved for future consideration of funding 03-Sacramento County. I Street Bridge Replacement Project. New two-lane bridge to replace existing two-lane vehicle crossing. (FEIR) (PPNO 1809). The Project is located over the Sacramento River and within the City of Sacramento in Sacramento County and the City of West Sacramento in Yolo County. The existing I Street Bridge and approach work are located between 3^rd Street in Sacramento to 5^th Street in West Sacramento. The new bridge location would be approximately 1,000 feet north of the existing I Street Bridge. The Project would replace the two-lane vehicle crossing (that is currently accommodated by the existing I Street Bridge) with a two-lane bridge on a new alignment. The new bridge would be 860 feet long with a 330-foot-long vertical lift movable bridge center span. The new bridge would have Class II buffered bicycle lanes and sidewalks on both sides. The Project includes partial or full removal of five bridge approaches. The Project is estimated to cost $334,738,000 and is funded through construction with Highway Bridge Program ($264,031,000), City of Sacramento local ($17,355,000), City of West Sacramento local ($17,352,000), Regional Surface Transportation Program ($11,000,000), and Local Partnership Program ($25,000,000) funds. Construction for the Project began in Fiscal Year 2025-26. For more details, see the full agenda item background.
(Source: October 2025 CTC Agenda, Agenda Item 2.2c.(4))

In February 2026, it was reported that a major financial hurdle was cleared following a vote by the Sacramento Transportation Authority to approve the project's financing framework for the I Street Bridge Replacement Project. Leaders say the project is fully funded, primarily through federal and state dollars. But that money arrives incrementally, not right away. The framework establishes a line of credit to provide cash flow for the construction costs, and STA has graciously stepped forward to be the lead in procuring that financing. Bids should be opened in March. As for what happens to the existing I Street bridge, the landmark river crossing is here to stay. West Sacramento is taking the lead on that project, and is going to maintain that upper-level deck for bike and pedestrian pathways. The construction start date depends on many factors, including how long the bid process takes. Right now, they are projecting that construction could break ground as soon as late May 2026. It is expected to take four years to build the bridge, with construction projected to wrap up in the summer of 2030.
(Source: CBS News Sacramento, 2/25/2026)

In April 2026, it was reported that the I Street Bridge replacement project, designed to connect West Sacramento and the Sacramento railyards, is facing delays after construction bids exceeded the $300 million estimate. The new bridge will replace the current span, which was built in 1911. When the initial round of bids were opened, the city received three bids ranging from $398 million to $517 million, far above the anticipated budget, with rising steel costs driving the increase. The lowest bid was $78 million above the high end of the original estimate. The project was originally scheduled to begin construction this year, but officials say global uncertainty and tariffs have contributed to the significant cost increase. West Sacramento has committed up to $21.2 million toward the project, but even with the removal of some decorative elements, officials say the overall cost won’t decrease significantly. City staff are expected to recommend rejecting the current bids and will reach out to contractors to get a better idea of current market conditions.
(Source: KCRA 3 Sacramento, 4/16/2026)

Sign Route 24 from Yuba City to Quincy

Rio Oso Reroutings In 1959, the CHC adopted a routing for a connection between the "future Route 232 (LRN 232) freeway" (today's Route 70 freeway routing) and the existing Route 232 highways (Feather River Blvd) near Rio Oso. This connector swings W from the adopted freeway route to join Feather River Blvd about a mile to the west. It is hard to see today, because although Feather River Blvd was "new" Route 24 (and later Route 70) at the time, it has since been relinquished by the state and downgraded to a county road. The plans called for the building of a two-lane bridge over the Bear River, upstream from the existing bridge. This is part of the first stage of construction of the new Route 70 freeway. The article indicated that when the LRN 232 freeway (today's Route 70) was extended to US 99E (Route 99) in Marysville, this connection would be incorporated into the Bear River interchange, and used as a county road connection (as LRN 232 would move off Feather River Blvd). However, in 1959, Feather River Blvd was new Route 24 headed north on El Centro Road from the Sacramento River. Old Route 24 resigned the Alt US 40 1955-64 alignment (current 113) from Woodland, which headed north at Tudor at the current junction of Route 99 and Route 113 then headed north into Yuba City. In this area for a small period of time (i.e., from 1964 until I-5 was completed and US 99 signs came down), California had both US 99 and California Route 99, but not on the same stretch of highway.
(Source: 1959 news clipping via Joel Windmiller, 1/27/2023)

Pre-1964 State Shield From Marysville, Route 24 ran through Oroville continuing through to Belden (this was LRN 87 (defined in 1933) between Robbins and Oroville, and LRN 21 (defined in 1909) to Belden, and is present-day Route 70), and then E through Twain, Quincy (running concurrant with Route 89) to Mohawk (this was LRN 21), and then by its lonesome to US 395 near Long Creek (also LRN 21).

The portion from near Cherokee and Quincy was under construction, and so a Temporary Route 24 ran from Oroville to Quincy through Berry Creek and Merrimac and Bucks (likely a temporary routing of LRN 21, 1934-1935, perhaps today's Route 162). The Feather River routing was used between 1935 and 1953. Later, a portion of Route 24 was redesignated as Alternate US-40 [1953-1964; for a while, cosigned as Route 24/US 40A] (and is present day Route 70), and Route 24 was truncated to the present day route of Route 99 and Route 113 and Woodland (pre-1964 LRN 87). Route 24, cosigned with Route 16, ran from Woodland to Sacramento. Later, that portion was taken from Route 24, becoming part of I-5.