Science Fair Project Encyclopedia
The Interstate Bridge is a pair of identical steel through truss bridges with a vertical lift that carries Interstate 5 traffic over the Columbia River between Vancouver, Washington and Portland, Oregon.
The bridge was built to replace an overcrowded ferry system operated by Pacific Railway, Light & Power Co. The first bridge was opened on February 14, 1917 at a cost of $1.75 million, which was shared between Clark County and Multnomah County. It was originally a toll bridge costing $.05 per person. In 1958 a $14.5 million upgrade created a southbound span and doubled the capacity of the bridge. The new bridge was built with a "humpback" that provides 72 ft of vertical clearance and minimizes bridge openings. At the time the new bridge was opened, the old one closed to give it the matching humpback. When both bridges were opened in 1960, tolls were reinstated at $.20 for cars, $.40 for light trucks, and $.60 for heavy trucks and buses, before being permanently removed in 1966.
A $3 million upgrade to the lift cables, expansion joints, and a deck repaving was completed in 1990. The diesel generator used to power the lift was replaced in 1995 at a cost of $150,000. In 1999 the bridge was repainted at a cost of $17 million. The Interstate Bridge is currently under an $10.8 million electrical upgrade that is scheduled to be completed in fall of 2005.
The bridge is 3,523 ft long with a main span of 531 ft. The vertical lift provides 176 ft of clearance when opened. The lift takes 10 minutes to open and does so between 10 and 20 times per month. In 2001 the 6 lanes of the bridges carried 120,000 vehicles including 10,000 trucks, operating at capacity for four hours every day. The estimated cost for a replacement bridge is $500 million to $1 billion.
- Wood, Sharon. The Portland Bridge Book. Portland: Oregon Historical Society, 2001. ISBN 0-87595-211-9.
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