The Washburn Tunnel is a two-lane underwater motor-vehicle tunnel connecting Galena Park and Pasadena, two suburbs of Houston, Texas. Completed in 1950, it travels north-south underneath the Houston Ship Channel. It was named after Harris County, Texas Auditor Harry L. Washburn. It is the largest and first toll-free vehicular tunnel in the Southern United States.

The Merritt Chapman and Scott Corporation of New York built the $7 million project. First, a trench 90 ft (27 m) by 40 ft (12 m) had to be dug. Second, the sections had to be locked into position 85 feet underwater. Finally, the last touches, such as tiling the inside, were completed.

It is the only underwater vehicle tunnel currently in operation in the state, as the Baytown Tunnel was replaced in 1995 by the Fred Hartman Bridge. The tunnel consists of a single bore, 895 meters (2,909 feet) in length, with a six-percent roadway grade outward from the center towards each exit. Forced transverse ventilation is potentially provided by three automatic high-speed Westinghouse Sturtevant blower fans located in a tower at the north entrance. These fans are designed to keep the air free from high-levels of carbon monoxide.

In the event of electrical failure, a generator can support the electrical needs of the tunnel. Every twelfth light is powered by a generator. The light intensity at the portals is three times brighter than the interior. This prevents temporary blindness when entering the tunnel.

Pumps located under the road surface counter accumulation of water by draining it back into the ship channel. Before Hurricane Ike in 2008, the tunnel had never flooded.

The tunnel is one of five vehicular crossings of the Ship Channel. The other four are the Sidney Sherman Bridge, popularly known as the (Interstate) 610 or Ship Channel bridge; the Sam Houston Ship Channel Bridge, formerly the Jesse Jones Toll Bridge and popularly known as the Beltway 8 Bridge; the Fred Hartman Bridge connecting La Porte, Texas and Baytown, Texas; and the Lynchburg Ferry. The tunnel is also the only 24-hour operation in Precinct Two.

The tunnel was added to the National Register of Historic Places on April 16, 2008.

On March 1, 2020, operations of the Washburn Tunnel, along with the Lynchburg Ferry, were transferred from Harris County Precinct 2 to the Harris County Toll Road Authority (HCTRA). There are no plans for HCTRA to implement tolls at either the Washburn Tunnel or the Lynchburg Ferry. Nevertheless, HCTRA's involvement will include plans to improve the operations of both facilities, as well as much-needed repairs and upgrades.

Total Cost: $7,683,915 (1950)

Total Length: 3,791 Ft.

Distance between Portals: 2,936 Ft.

Length of Tube Section: 1,500 Ft.

Roadway Width: 22 Ft.

Headroom (each lane): 13 Ft.

Headroom (center Lane): 18 Ft.

Internal Diameter of Tubes: 32 Ft.

External Diameter of Tubes: 38 Ft.

Max. Grade: 6%

Max. Dept (Water to top): 45 Ft.

Max. Dept (Water to roadway): 68 Ft.

Max. Dept (water to bottom): 80 Ft.

Dredging: 425,273 cu. yards

Excavation: 289,600 cu. yards

Tremie Concrete: 11,750 cu. yards

Concrete: 34,250 cu. yards

Steel in tubes: 2,373 tons

Ceramic Tile: 1,061,000

Number of fans: 3

Max Ventilation: 760,000 cfm

Complete Air Exchange: 2 minutes

• Harris County Precinct 2 from Harris County's Precinct 2
• Washburn Tunnel from Harris County's Precinct 2
• Washburn Tunnel 17 Images from Bridgehunter.com
• Washburn Tunnel at Structurae