BOSTON — The Massachusetts Department of Transportation is getting ready to switch the exit signs along part of Route 128 to a mileage-based system. Work on the signs along Route 3 is expected to be finished on Tuesday and installations along Route 128 from Gloucester to Peabody will begin Wednesday. The swapping of signs along that part of Route 128 is expected to last about eight days, MassDOT officials said. The exit numbers are being changed by MassDOT to comply with federal highway mandates, which require mile-based exit signs. Massachusetts is one of three states that have not yet begun...