The transport minister is defending the government's plans to reverse blanket speed reductions, saying the government is taking a "balanced approach".

The government wants to scrap blanket reductions - introduced under Labour at the start of 2020 - on suburban streets, arterial roads and state highways by July 2025.

The proposal will also allow limits of up to 120km/h on new roads of national significance built to accommodate that speed.

The new legislation is set to be introduced by the end of September, with public consultation closing this Thursday.

The government argues that the change will boost productivity and economic growth.

Former chief science adviser for the Ministry of Transport, Simon Kingham, criticises the proposal, saying it will increase the number of road casualties and injuries, deaths by air pollution, as well as increase greenhouse gas emissions.

Simeon Brown tells RNZ the government has taken a balanced approach to the issue after a cost-benefit analysis, and that there will be safety measures in place.

"We're ensuring that there are going to be slower speed limits around schools, we'll be mandating slower speed limits during pick up and drop off times to ensure young New Zealanders are kept safe... but it makes absolutely no sense to make a shift worker going to work at 4am  have to crawl around the streets at 30 kilometres per hour in their car when there's no one else walking along the road," he says.

"We need a balanced approach to this issue rather than slowing people down."

Brown says there's strong evidence to show that New Zealand doesn't need a blanket approach on speed limits.

Rather it needs a policy that allows for rigorous cost benefit analysis, and a targets approach to where there are safety risks, he says.

Meanwhile, some councils have voiced concerns over the government's proposal.

Councils in Marlborough and Tauranga are pushing ahead with speed reductions, but Christchurch City councillors have expressed concern.

Just last week, Auckland Council's transport and infrastructure committee voted overwhelmingly - 18 votes to three - to oppose the government's directive.

-RNZ.