The first phase of the Southern Parkway, a Washington County highway that will someday become a beltway encircling I-15 as I-215 does in Salt Lake County, was opened to traffic Tuesday.

Phase I of the Southern Parkway is four miles along the Utah-Arizona border, extending from I-15 at the newly created Exit 2 to River Road. From River Road motorists can reach the Fort Pierce Industrial Park, an industrial business area for St. George, said Utah Department of Transportation spokesman Kevin Kitchen.

The four-mile stretch shoots off I-15 to the east. It cost $58.5 million and includes three interchanges — at I-15, River Road and with the frontage road. The School and Institutional Trust Lands Administration is developing housing off of the frontage road and SITLA helped pay for that interchange, Kitchen said.

The divided highway has two lanes in each direction. Speeds are 60 mph.

"It's like an actual freeway," Kitchen said. "There are no stoplights, except over I-15, at this point. We're calling it a parkway, kind of like how Legacy works. The intention is it'll be a corridor with limited access."

The next phase of the Southern Parkway heads to a new St. George airport that's under construction. That phase will be completed in fall 2010, Kitchen said.

The timeline for the remaining four phases of the 40-mile project is not yet set because it depends on funding and land purchases. The cost is estimated at $475 million for the completed project.

The Southern Parkway will ultimately loop between Exit 2 and state Route 9, a road off of I-15 that leads to Hurricane and to Zion National Park. State Route 9 will need improvements to handle the increased traffic.

"The idea is this will take care of a 30-year transportation need for us," Kitchen said.

Washington County is one of the fastest-growing regions of the United States.

According to the U.S. Census Bureau, the population of Washington County in 2008 was 137,589, up from 90,354 in 2000 and 48,560 in 1990.

E-MAIL: lhancock@desnews.com