WOODSTOCK – A medical helicopter is on the ground and police are blocking traffic on state Route 120 between Greenwood and Thompson roads after a multiple-vehicle accident this morning. The McHenry County Sheriff’s Office issued an alert just after 10 a.m. advising people to avoid the area for the next four hours. The alert says a life could be in danger. First-responders from the Bull Valley Police Department, Woodstock Fire Department and the sheriff’s office are working at the scene.