A road safety campaigner has lambasted Waka Kotahi over its failure to meet median barrier targets.

A Road to Zero target aims to have 1000km of median barriers by 2030, but is projected to fall short by half.

But the agency has surpassed its target of assessing speeds on 10,000km of road.

Motorsport champion and road safety advocate Greg Murphy told Mike Hosking all he's seen from Waka Kotahi is excuses for not meeting the target.

As of December, Waka Kotahi spent $62 million on campaigns to support Road to Zero.

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