Approaching the town of Port Barre, Louisiana –West Bound–the Highway speed limit is 60 MPH. There is an advisory sign a few hundred yards ahead of a 45 MPH speed limit sign. I was stopped at night as I crossed the 45 MPH sign at about 54 MPH. The officer stated he clocked me at 61 MPH at the point I passsed the sign. It was dark, the officer crossed the median from the East bound lane to stop me. I was travelling at 45 MPH prior to the second 45 MPH sign a few hundred yards past the first 45 MPH sign. The officer allowed no time for me to decelerate from 60 MPH to 45 MPH in the distance provided between the advisory sign and the 45 MPH sign.