The weather activated variable speed limit signs that were vandalised on the Kaimai Range have been replaced at a cost of $75,000.

The signs along State Highway 29 were temporarily shut down last month when batteries, storage cabinets and cameras were stolen or tampered with.

The Transport Agency has increased security on the signs by installing anti-theft devices on the cabinetry, including alarms and surveillance.

NZ Transport Agency project team manager John McCarthy said the signs were put in place in a bid to "reduce the number of people being killed or seriously injured on SH29 over the Kaimai Range and were designed to encourage people to drive at safe speeds that are appropriate to the road conditions when rain, ice and fog hit the Kaimai Range".

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Data shows more than 70 per cent of the crashes on the range happen in wet weather, and more than 40 per cent of these were caused by drivers travelling too fast for the conditions.

"With winter settling in we want to remind people to drive to the conditions, reducing their speed and increasing following distances during adverse weather," McCarthy said.

The trial started in November 2015 and data from the trial is being analysed.

Results from the first year of the trial showed there was a reduction in the number and severity of crashes and it was decided the signs would stay in place until the outcome of the trial was known.