A supporter of speed limit reductions says it won't slow down most commuters in Auckland's CBD.

Auckland Transport will decide today on whether to reduce speeds on 800 kilometres of roads in the Auckland region.

It could include 30 kilometre limits on Hobson, Nelson and Fanshawe Streets.

Greater Auckland spokesman Matt Lowrie told Mike Hosking the speed limit reductions won't have much impact on the rush-hour commute.

"Most people aren't travelling at 30kmh through the central city anyway, it's just too busy and congested."

LISTEN TO THE INTERVIEW ABOVE