Police were called to reports of “ridiculous” brick-throwing from two motorway bridges in dense fog.
Passersby phoned for help after witnessing youths throwing bricks and pieces of concrete off the motorway bridges in Pope Lane and Longridge Road, Ribbleton, at 7.30pm on Sunday.
A police spokesman said: “Numerous patrols attended but the youths made off prior to arrival. Needless to say this behaviour is absolutely reckless that could easily result in serious collisions on the motorway.”
Officers urged parents to keep a check on where their children were.