Police will be monitoring speeds "closely", with some extra attention to passing bays in the zone.
"They're not speed zones," he said. "They're for slower vehicles to move over and let other traffic past, but they're not for the other vehicles to speed up over the limit to get past."
He said that while the rate of fatalities on Hawke's Bay roads had dropped in recent
months, there was little change in the number of serious injuries, meaning there is still "work to do" in getting motorists to drive to the conditions and slow down.
Some of the monitoring of speeds between Napier and Hastings relates to other possible safety improvements in the future.
The changes took into account the crash rate, which included three separate fatal incidents in the 3km between the SH51 intersections with Ellison St and Awatoto Rd in 20 months up to mid-May last year, the lower-than-normal mean speed of motorists well below the 100km/h limit, and public consultation.
Meanwhile, the Napier council on Thursday voted to start consultation on more changes which emanated from concerns raised in consultation leading to the changes which start on Monday.
In addition, the council proposes changes on Willowbank Ave (100km/h to 80km/h), and school zones in Battery Rd and Guppy Rd (both 50km/h to 30km/h), and Hill Rd (80km/h to 40km/h).