The city’s new 120-space parking lot at the former Universal Steel site at 297 Bridge St. is now available for public use. The newly paved surface lot opened Oct. 19. Parking in the lot, a short distance from the Salem commuter rail station and the downtown, is free — with one exception. The city authorized parent volunteers from the High School music program to collect $15 per car starting at 9 a.m. on Saturday and Sunday and $20 per car on Thursday, which is Halloween. Proceeds will support the school band’s fund drive for new drums, uniforms, and instruments. The adjacent lot, formerly Alpha Auto Sales at 295 Bridge St., is also available for parking. Parking in that lot, which the city leased this spring to provide another 30 spaces, is free with the exception of the same collection by the music program this weekend and on Halloween. The city partnered with the US Environmental Protection Agency and the Massachusetts Department of Environmental Protection over several years to dismantle the abandoned factory on the lot, remove contaminants, and pave it for parking. The city’s long-term goal is to sell the lot for development once the nearby MBTA parking garage project is complete in late 2014.