SEATTLE -- Angela Danadjieva's master plan for Interstate 5 in Seattle, the most extensive freeway air-rights development in the nation, has demonstrated how pedestrian access severed by major transport routes within a community can be successfully reclaimed.

The Bulgarian-born environmental architect, who has devoted 20 years to the state-sponsored project, compares such immense traffic corridors to giant canyons that reduce the element of humaneness in a city.

I-5 is a 12-lane highway that passes through downtown Seattle. The project is the first attempt to aesthetically reconnect Seattle's downtown to its residential areas.

Much of the success of Washington's pioneering freeway development, Danadjieva believes, can be measured by its success in reversing declining property values along the traffic corridor and encouraging development.

As a result of development above and along the freeway corridor in the last 12 years, downtown Seattle has gained 1,254 new hotel rooms, 160 residential units, 1.9 million square feet of office space, 128,000 square feet of retail space, 3,300 garage spaces, an eight-acre park and a 370,000-square-foot convention and trade center.

One of the major elements spanning I-5 is the new Washington State Convention and Trade Center, now in its final stages of construction.

"What we have demonstrated here is a transformation of environmental liabilities into urban open space with multiuse amenities and greater pedestrian access," Danadjieva said. The Washington State Convention and Trade Center, with its massive steel truss grid rising diagonally above the freeway, is a $160 million, 370,000-square-foot complex containing 140,000 square feet of exhibit and meeting space, indoor parking for 1,000 cars and a 30,000-square-foot grand lobby and winter garden.

It is 70 percent completed and is scheduled to open in 1988. The complex, with its proposed shopping galleria and extensive terraced grounds, is adjacent to the historic, multiuse Eagles Auditorium.

Before forming her own company -- Danadjieva & Koenig Associates, with her husband, Thomas Koenig -- Danadjieva was associated with Lawrence Halprin Associates and designed Seattle's landmark Freeway Park.

The first of its kind in America, Freeway Park acts as a lid over I-5 and provides a five-acre oasis incorporating a spectacular 32-foot sculptured waterfall with 10,000 gallons of water cascading over it every minute.

"After the construction of the I-5 Freeway in Seattle in the '60s, the real estate values along the traffic corridor dropped drastically and interest in the adjacent development ceased," Danadjieva said.

"The subsequent lidding of the I-5 canyon transformed the environmental liability into an urban amenity in a multiuse plan that incorporated a pedestrian network, parking facilities, interior and exterior civic amenities and landscaped parks, all above the I-5 traffic."

The Pigott Memorial Corridor -- another segment of the Seattle freeway project that was completed in 1984 -- spans a 40-foot grade differential connecting the existing Freeway Park to the First Hill community.

"In that project, we took advantage of the grade differential in that segment to design a wheelchair-accessible ramp-stair, thus making the corridor available to everyone," the architect explained.

The partially elevated concrete structure meanders through a parklike environment with seating platforms, plazas, fountains and terraces overlooking the downtown skyline.

Construction costs on the project were significantly reduced by combining elevated and on-grade concrete structures and designing the five water features as a single mechanical system.

Danadjieva's approach to design is bold. "I work with large-scale configurations -- stylized concrete boulders, immense earth berms, gigantic walls and cascading waterworks. With freeway projects, we are not dependent on expensive materials and finishes."

She said that an important aspect of the faceted concrete configuration -- the giant boulders, earth berms and dense greenery -- has been that air quality has improved and traffic noise has been curtailed.