LIVERMORE -- A ceremony was held here Thursday to mark the start of construction on a 13-mile new carpool lane on westbound Interstate 580, which is hoped will help ease traffic congestion.

The $145 million new lane will be added on I-580 between Greenville Road in Livermore and the Foothill Road over crossing in Dublin and Pleasanton. Completion is expected in late 2014, a year before the lane is to be converted into an express toll lane open to carpools for free and solo drivers for a toll.

Contractors also will add an auxiliary lane on I-580 between Isabel Avenue and First Street in Livermore.

The new carpool lane is paid for by Alameda County's half-cent transportation sales tax, Bay Area bridge tolls, and state and federal funds.

The Alameda County Transportation Commission and Caltrans are jointly developing the project with assistance from the Metropolitan Transportation Commission.