The California High-Speed Rail Authority proposes to build 520 miles of tracks between San Francisco and Los Angeles, via the central San Joaquin Valley, for electric trains traveling up to 220 mph. The cost is estimated at about $98 billion.

Supporters say high-speed trains will ease freeway congestion, improve air quality and cut travel time. Opponents say the plan is unproven, extravagant and disruptive to farms, homes and businesses.

Work could begin late this year in Fresno on the first section between Merced and Bakersfield, described by planners as the backbone of the statewide system and scorned by others as a route unlikely to see many passengers.

No high-speed trains would run on the system until it reaches either the Bay Area or the Los Angeles Basin, and those sections can be built only as money becomes available. Ultimately, plans call for service to Sacramento in the north, and through the Inland Empire to San Diego in the south.

For the first leg, the authority has more than $3 billion in federal stimulus and transportation money in hand and hopes to match that with nearly $3 billion from Proposition 1A, which California voters approved in 2008. But first, the state Legislature must decide whether to authorize the sale of Prop. 1A bonds.

It’s unclear who will lead the agency after a recent shakeup. Roelof van Ark, rail authority CEO, announced his resignation last week. Board member Manuel Toledo resigned Dec. 31, when his term expired, and Thomas Umberg will step down as board chairman in February but remain on the board. Two key staffers, deputy director Dan Leavitt and press secretary Rachel Wall, have resigned.