Caltrain says it expects to release a Request for Proposals to prequalified bidders early next year after the project receives environmental clearance. A draft environmental impact report was published in March.

The cost of the project is estimated at $US 1.2bn, with a further $US 440m required for the acquisition of a fleet of electric commuter trains. Caltrain expects electric trains to provide 75% of its total service by 2019, with diesel traction remaining for services running beyond San Jose.

As well as benefitting commuter rail operations the upgrade will allow California High-Speed Rail services to run into San Francisco on Caltrain infrastructure.

Caltrain currently carries around 54,000 passengers per day and says peak hour trains are running at capacity.