I've been working on designs for two bike/pedestrian path sweepers that can be towed by bicycles. Both would be mounted on the belly of a B O B trailer (Ibex model trailer might be better with its suspension). One would be traction drive from the trailer's rear wheel to a rotary tube broom. The other would house a small motor in the trailer that would drive the rotary tube broom. Seems like the motorized broom would be significantly easier on the person pedaling in spite of the additional weight.