Editing Caldecott Tunnel (section)

===Third bore and traffic reversal===
[[File:Caldecott Tunnel.jpg|right|thumb|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. Bore 2 was serving westbound traffic at the time of this photograph.]]
By 1960, the Division of Highways had rebuilt the eastern approach to the tunnel into a 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.<ref>[https://archive.org/details/cavol3940liforniahigh6061wa00calirich/page/n263 ''California Highways and Public Works'', Official Journal of the Division of Highways, Department of Public Works, State of California, Vol.39, Nos.7-8, July-August, 1960, p.31]</ref>

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. The new third bore made it possible to provide four lanes to accommodate the heavier commute-direction traffic by [[Reversible lane|reversing the traffic flow]] of the middle bore.

The third bore also brought new technology to the tunnel with the installation of the "pop-up" lane control. Plastic lane [[delineator]]s 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.<ref>{{cite web | url=http://www.caldecott-tunnel.org/project-overview/history-caldecott | title=History of the Caldecott | work=The Caldecott Tunnel Fourth Bore Project | access-date=October 8, 2013 | archive-url=https://web.archive.org/web/20140202105048/http://www.caldecott-tunnel.org/project-overview/history-caldecott | archive-date=February 2, 2014 | url-status=dead | df=mdy-all }}</ref>

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.<ref>[http://libraryarchives.metro.net/DPGTL/Californiahighways/chpw_1960_marapr.pdf ''California Highways and Public Works'', March-April, 1960, p.9]</ref>

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 Route 13 (California)|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]].