A new road safety advertising campaign is challenging speeding drivers to slow down and stop defending their perceived 'right' to speed.

The campaign, run by the NZ Transport Agency (NZTA) and NZ Police, addresses a large number of motorists who drive too fast for the conditions.

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Statistics show that every week 11 people are seriously injured or killed in a speed-related crash on New Zealand roads, says NZTA director of safety Harry Wilson.

"A substantial portion of our society does not see the connection between speed and crashes... that needs to change because the facts and the physics are indisputable," he said.

"The simple and inescapable truth is that less speed means less harm in a crash."

Police say that a small change in speed makes a big difference to injury severity, and are pleading with all drivers to be courteous and slow down to make sure they get to their destination safely.