From the website-
“IT’S PITTSBURGH,
“I wanted to showcase the hills.”
January 26, 2011
It’s a one-day bicycle ride around Pittsburgh. It covers 13 very steep hills. It’s a test of strength, endurance, biking skills and human perseverence. It’s called the DIRTY DOZEN. It was started in 1983 by Danny Chew, his brother and some of their friends. It’s now a Pittsburgh tradition and an extraordinary celebration of our city’s terrain!”
Via Bicycle 