An extension of State Route 202 (aka Loop 202) in the Phoenix area has received final federal approval, clearing the way for construction of the nearly $2 billion project to begin, the Arizona Department of Transportation announced earlier this month.

The South Mountain Freeway stretch of SR 202 will run from Interstate 10 at Pecos Road in the East Valley to I-10 at 59th Avenue in the West Valley. It's intended to allow traffic to bypass the often-congested stretch of I-10 through downtown Phoenix.

The project has languished since 1985, when it was included in a ballot proposition approved by Maricopa County voters. It's been one of the more controversial freeway projects in recent memory, with environmentalists, Ahwatukee Foothills homeowners and the adjacent Gila River Indian Community voicing concerns about the plan.

ADOT considered several different routes for the 22-mile-long, above-ground freeway. From east to west, the final route follows Pecos Road before it cuts northwest, then north along 59th Avenue. A mile of the freeway will pass through the southwestern edge of South Mountain Park and Preserve, the country's largest municipal park. ADOT says only 31.3 acres of the 16,094-acre park will be affected.

Freeway construction is slated to begin early next year, and the freeway should open by 2020, ADOT said in a statement.

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Photo: The final route for the South Mountain Freeway stretch of State Route 202. | Courtesy of Arizona Department of Transportation