View Larger Map Be aware that traffic heading north on Massachusetts Ave. NW this evening could still be experiencing even more backup than usual due to an earlier scaffolding collapse at the Foxhall Condominiums. Two construction workers were injured — one with a serious head injury, the other with two broken legs — when a 30-foot-tall scaffolding behind the building at 4200 Mass. Ave. NW fell down while the workers were atop it. The collapse…