Caldecott Tunnel

In November 1926, the Counties of Alameda and Contra Costa, and the City of Oakland agreed to the construction of a new tunnel through the Berkeley Hills to replace the old, small, decrepit and increasingly inadequate existing tunnel.[10] In 1929, Alameda and Contra Costa County formed Joint Highway District 13 to accomplish this goal.[11] Surveys and preliminary work on the approaches began in 1931.[12][13]

On June 17, 1934, construction of the first two bores of the Caldecott Tunnel began.[14]

The project included an extension of Broadway from its existing termination point below the hills some two miles from the planned west portal of the new tunnel. This required some major earth-moving efforts, both cutting and filling as well as buttressing, especially up in Temescal Canyon. This included filling in one of the inlets of Lake Temescal as well as part of the upper canyon where Broadway was to run.

The entire project was completed in 1937, and the tunnel opened to traffic on December 5 of that year.[15] The tunnel was named the Broadway Low Level Tunnel (commonly shortened to Broadway Tunnel), since the principal through access was from Broadway in Oakland, and was located below the portal of the old Inter County Tunnel. However, access from Ashby Avenue was retained as it was designated the connecting thoroughfare from the Eastshore Highway (re-engineered as a freeway in the mid 1950s) and the new San Francisco–Oakland Bay Bridge, and dubbed State Highway 24. The approach to the east portal on the other side of the Berkeley Hills was via Mount Diablo Boulevard, also at that time part of State Highway 24.

In 1960, the Broadway Low Level Tunnel was renamed, becoming the Caldecott Tunnel.[16]

The Caldecott Tunnel prior to the construction of the fourth bore as seen from the western end. From left to right: Bores 3, 2, and 1.

By 1960, the Division of Highways had upgraded the eastern approach to the tunnel into a modern freeway. With Contra Costa County accessible by freeway, its change from an agricultural community into a major suburb accelerated.

The Division of Highways purchased sufficient right-of-way to the north of the existing twin bores to build another pair of bores. Given the traffic counts and the expense of tunnel construction, the construction of two additional bores would have been seen as unnecessary and extravagant. However, with the traffic count exceeding 50,000 vehicles per day, the state embarked on a project to build a third bore at the Caldecott Tunnel.[17]

The project broke ground in 1960 and was opened to traffic in October 1964. When the third bore was opened, the other bores were closed one at a time for maintenance, including the installation of a continuous row of fluorescent lights. Eventually the new third bore made it possible to reverse the traffic flow of the middle bore, providing four lanes to accommodate the heavier commute-direction traffic.

The third bore also brought new technology to the tunnel with the installation of the "pop-up" lane control. Plastic lane delineators were set in tubes within the pavement. With the touch of a button, water would fill tubes to cause the delineators to pop up from the pavement; the middle bore was closed to one direction of travel, while opening it to another. During the week, the middle bore of the Caldecott was reversed between 2:00 am and 5:00 am to favor westbound traffic, and then switched again sometime between 11:30 am and noon to favor eastbound traffic. Ballgames, concerts and other events made balancing weekend traffic through the tunnel very difficult. It was not uncommon to reverse the middle bore six times on a Saturday or Sunday. The pop-up system still required substantial manpower to implement. While it did eliminate the need to set down individual cones to separate traffic, Caltrans maintenance workers had to direct traffic out of the closing lanes to prevent vehicles from getting caught on the wrong side of the pop-up delineators.[18]

A portion of the material excavated for the third bore was used in the construction of embankments for the MacArthur Freeway project between the MacArthur Maze and Broadway in Oakland.[19]

In the late 1960s, the Grove-Shafter Freeway was completed and replaced Broadway as the main route to the Caldecott Tunnel from Oakland as well as replacing Ashby for traffic coming from San Francisco. Ashby Avenue and Tunnel Road were redesignated State Highway 13 and aligned with the new Warren Freeway through the Montclair District of Oakland. The Grove-Shafter Freeway was then designated State Highway 24. In 1980, the freeway was renamed after William Byron Rumford.

On April 7, 1982, an accident involving a gasoline tanker truck in the third (then-northernmost) bore set off the Caldecott Tunnel fire.[20] The accident caused major damage and the bore was closed to traffic for several months while repairs were made, with traffic temporarily reverting to the pre-third-bore configuration. During the fire, the tunnel acted as a natural chimney, venting the smoke, flames and heat uphill towards the eastern entrance to the tunnel. The accident and fire killed seven people, most of whom were overcome by toxic smoke. The fire occurred shortly after midnight when there were few cars in the tunnel; had it occurred during normal commute hours, hundreds could have died. As a result of the fire, it is now illegal to transport hazardous material in a tanker truck through the tunnel, except between the light-traffic hours of 3:00 am and 5:00 am.[21]

On October 20, 1991, the catastrophic Oakland firestorm started on the ridge north of the Caldecott Tunnel. The fire spread quickly west down both sides of the west portal of the tunnel and jumped the freeway, eventually killing 25 people and destroying over 3,000 homes, apartments and condominiums.

The Caldecott Tunnel was designated a City of Oakland Landmark in 1980, and received a Preservation Award from the Art Deco Society of California in 1993.

To relieve traffic congestion in the reverse commute direction, the California Department of Transportation began planning for a fourth bore in 2000. In 2007, the California Transportation Commission approved the final funding needed to build the fourth bore.[22] Construction started in 2010.[23] Commencement of the project was stalled as a result of the financial crisis of 2007–2008, but was quickly back on track as a beneficiary of President Obama's American Recovery and Reinvestment Act of 2009 (ARRA).[24][25] Construction got underway until completion in 2013.[26][27][28] Much of the excavated material from the bore was trucked to Treasure Island for use in soil augmentation and remediation during the subsequent redevelopment of the island.[29]

The fourth bore contains a roadway with two 12-foot-wide (3.7 m) traffic lanes, one 10-foot-wide (3.0 m) shoulder, and one 2-foot-wide (0.6 m) shoulder,[30] ventilation, air and traffic monitoring systems, traffic lights, and electronic message boards.[31] There are emergency exits to the third bore. When the fourth bore was opened to traffic, the need for the daily traffic reversal was eliminated; two bores (four lanes) serve each direction at all times, although individual bores may be closed during periods of light use for maintenance purposes.[32]