That's because posted speed limits will still apply, so if the sign says 65, the speed limit remains at 65 until the sign is replaced. New signs won't start going up until January 2nd, and the Department of Transportation estimates it will take about a month to replace them all.
900 new speed limit signs will go up in all. It cost about 200-thousand dollars to make them. 87% of interstate highways will be posted at 70 MPH. But only 28% of tollway highways will be part of the new speed limits, because many are in urban areas or under construction.