Kaiapoi High School has installed a road sign outside its front gate that warns of "teenagers crossing".

The yellow sign features two teenagers, with their heads looking down at their cell phones.

It was born out of concern about the 100 kilometre motorway zone that finishes just before the school.

Principal Bruce Kearney said with 500-distracted students leaving school at the same time everyday, they want to make motorists aware of what's ahead.

"I suppose it's just more highlighting an issue that please be a little more understanding of our people crossing. They are teenagers. They are hooked into their technology. They do tend to not look left and right before they cross."

He's noticed more awareness since the signs went up at the start of term, and he's more than willing to have other schools copy the idea.

"I think it's nice to have them anyway, just so people are aware and it's more appropriate for schools. It would be awesome if they were using it too."

The high school is still working on developing a permanent traffic management plan with the Waimakariri District Council.