Sorry - my error - Somerville PD is sometimes heard on 453.55 doing special events or undercover ops
453.50 is Somerville DPW - Somerville PD might have 453.50 in some radios but I have never caught Somerville PD on 453.50 - not that I listen to the channel much - I think I have heard EMA or the Fire Wire guys on 453.50 in the past