Commuters in Pittsburgh used to seeing steel and concrete across the city's Andy Warhol Bridge got a colorful surprise this morning thanks to more than 1,800 knitters who covered the bridge with yarn.

The result of the knitters' weekend work, and more than 18 months of planning, is 580 blanket-sized panels flanking the bridge's pedestrian walkways. Each of the 72-by-34-inch acrylic panels was knitted by hand.

"What's amazing about this project is how many people it's brought together," Penny Mateer, co-director of Knit the Bridge, told the Pittsburgh Post-Gazette. "Thinking of the bridge as a metaphor, it's bridging differences and getting people to meet each other."

Volunteers worked on the bridge - closed for the day to vehicle and pedestrian traffic - until nearly 10 p.m. Saturday, covering it in roughly 3,000 feet of yarn. The yarn will remain on display through the weekend of Sept. 6.

The Fiberarts Guild of Pittsburgh, which organized the roughly $100,000 project through endowments and individual donations, called it the nation's largest "yarn bomb."

Adding a high-tech element to the project, its lead design artist, Amanda Gross, told the Post-Gazette that the knitted panels were numbered and cataloged as they were installed so that knitters would eventually be able to locate - through a database and possibly a smartphone app - their work on the bridge.

"[It's] a tool for community building and community organizing, and creating positive change in the world," Gross was quoted as describing the project.

For more information visit the Knit the Bridge website at www.knitthebridge.wordpress.com.