California officials are marking the start of work on a high-speed rail system. Here is a look at some of the facts about the project:

Q: How much will it cost?

A: The current price tag is listed as $68 billion, but California's High-Speed Rail Authority says it is still cheaper than building dozens of new airport runways and highways to accommodate a state population expected to hit 46 million by 2035.

Q: Who is paying for it?

A: The state agency that oversees the project has nearly $10 billion in voter-approved bonds for rail construction and improvements to existing lines, and $3.3 billion in federal financing. Authorities are hoping for private investment in advertising and development around stations.

Q: Where will it go?

A: Construction starts in the Central Valley, a 28-mile stretch from Madera to Fresno. In future years, the rail line will stretch north to San Jose and south to Palmdale and the San Fernando Valley north of Los Angeles.

- Associated Press