SACRAMENTO -- Contractors vying to build the first sections of California's proposed high-speed rail line will get the green light to start making their bids within just a few weeks.

On Thursday, the California High-Speed Rail Authority approved the terms and conditions that bidders will be expected to meet in designing and building a 29-mile segment of the line from east of Madera to the south end of Fresno -- a stretch that is expected to cost about $1.5 billion.

The request for bids still must be approved by the state's Public Works Board, but after clearing that hurdle, five potential teams of construction companies from across the U.S. and around the world can begin making their bids.

Contractors are expected to submit bids by August or September, and the winner could be chosen by the end of the year. No contract can be awarded, however, until environmental reports for the Fresno-to-Bakersfield section are finished and certified by the state rail authority and the Federal Railroad Administration -- a process that is not expected to be done until late this year.

Roelof van Ark, who is retiring as the authority's chief executive officer, said there are some smaller construction projects -- including an extension of the Fresno Street underpass to below G Street, the proposed high-speed line and the existing Union Pacific Railroad tracks -- that are not part of the major contract and could begin earlier, once environmental reports for the Merced-Fresno section are approved.

The environmental assessment for Merced-Fresno, which includes the site of a station in downtown Fresno at Mariposa Street, is much farther along than the southern section. Van Ark said a final version of the report has been submitted to federal agencies for review and is expected to be released in time for the authority's board to give its final approval -- including finalizing the proposed route -- at its meeting in early May.

The project includes 12 street overcrossings or underpasses, two elevated viaducts, a tunnel and a bridge across the San Joaquin River. Laying the tracks will be done later under a separate contract.

As the prospective prime contractors start work on calculating bids to design and build the line, the rail authority is ramping up efforts to link prospective subcontractors with the major companies.

"We are doing everything we can to try to put people who are interested in subcontracting, or being involved with these primes, together with these companies," said Lance Simmens, a spokesman for the authority. "We already have a very active and aggressive small-business outreach, and we will accelerate that in the coming months to make sure we can hook people up."

Among the terms to which the prime contractors must agree is a goal of providing 30% of its subcontracting work to small businesses, including minority- and women-owned businesses and businesses operated by disabled veterans. Van Ark has said the goal is intended to ensure that the project stimulates jobs for companies and in communities that need it most.

While the goal does not include penalties if a contractor doesn't meet that level, a contractor could be declared to be in breach of contract if it fails to make a good-faith effort to hire small-business subcontractors, said Pat Padilla, who leads the authority's anti-discrimination planning and program efforts.

The work through Fresno is the first of five construction packages on the line between Merced and Bakersfield, a 130-mile stretch that would form the backbone of a system ultimately connecting the San Francisco Bay Area with the Los Angeles Basin. The cost to fully build the 520-mile system is estimated at $98 billion.