Reply Repairs will include milling and paving the lots and creating a bioretention area with plantings in order to eliminate washouts. (Harford County) BEL AIR, MD – The parking lots at the Ma & Pa Trail's Williams Street trailhead in Bel Air will be closed for repairs starting on Monday, May 17. The closure is expected to last three weeks. Repairs will include milling and paving the lots and creating a bioretention area with plantings in order to eliminate washouts. Subscribe Visitors should park in the lower lot of the Liriodendron Mansion, located at the end of Broadway about two blocks from the Williams Street trailhead.