When completed, the new Central Park Boulevard Interchange is expected to serve up to 18,000 daily drivers.
This weekend, crews will close lanes on I-40 in both directions.
When completed in 2013, the project will replace the 73-year-old Doyle Drive southwest of the Golden Gate Bridge.
State Road 9B project has been stalled since the mid-1970s.
Recovery Act funds will go toward the total replacement cost of $129.5 million the Milton-Madison Bridge.
Familiar freeways top the rankings of best, worst and most improved roads in Overdrive survey
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