The bridge should help traffic flow between Phoenix and Las Vegas now that drivers do not have to slow down to cross over the Hoover Dam. Traffic over the Dam will be suspended once the bridge is fully operational.
The 1,900 foot bridge sits 890 feet above the Colorado River and has a price tag of $240 million. Planning for the project began in the late 90's with approaching roads beginning construction in 2003. The bulk of the bridge construction started in 2006.
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Source: Wiki.