See this page on the KCDC website.

This is all pushed by orders from this government based on its Climatism religion, not safety concerns. The only possible exception in regards to safety is around schools, where a 35 km/h limit can be justified during schooldays between 8:30 am to 4 pm up to a distance of 200 metres from the school.

The Climatists think that if everyone drives at 20 km/h slower, they’ll use less petrol — but has this government tested that assumption emperically and independently? Much about lower petrol consumption is determined by factors such as driving at a smooth steady speed, gentle accleration, having correct tyre pressure and reduced weight carried. Cars are also most fuel efficient driving at 50 in 4th or 5th gear rather than 30 stuck in 2nd gear.

Slowing everybody down is also why this government has cut back on road maintenance:

From Simeon Brown, National Party Spokesperson for Transport:

Have you heard the news about how Labour has continued to turn a blind eye to State highway and local road maintenance through this year’s Budget?

The funding for State highway and local road maintenance has decreased by millions in this year’s National Land Transport Fund Budget allocation, with State highway maintenance decreasing by $164 million and local road maintenance decreasing by a massive $314 million.  

The reality is that Labour has spent money in all the wrong places, including funding cancelled cycle bridges, speed limit reduction plans, and land acquisition for the failed Auckland Light Rail.

With 54,000 potholes needing repair last year alone, this money would have been better spent on fixing the record number of potholes on our State highways.

Labour’s approach to transport spending means that Kiwis can expect more potholes on the roads and less maintenance of our State highways and local roads.

National will bring fiscal discipline back to transport spending by focusing on the infrastructure projects that matter to New Zealanders. We will ensure that the National Land Transport Fund is primarily focused on maintaining our roads, including fixing the potholes that pepper our highways.

The choice is clear, and the election is four months away.