A police exercise is taking place Thursday in Danbury.  A Traffic Alert has been announced by Western Connecticut State University due to police training on the midtown campus.  Members of the Danbury and West Conn police departments will conduct a training exercise that will affect traffic on Eighth Avenue.  The exercise will concentrate in the Litchfield Hall residence hall.  From 7 am to 4 pm on Thursday, traffic on Eighth Avenue will be restricted to residents only.  Police officers, including members of the Danbury SWAT team, will be involved in the training.