In the bike-mad Netherlands, the national phone company is developing a smart way to stop kids texting while cycling -- a growing cause of teenage accidents.

A new app from phone company KPN will block internet and phone signals to a cyclist's smartphone while they are in the saddle.

"This system is part of a broad campaign to highlight to children, the most vulnerable, the dangers of using their smartphone on their bikes. These are two things that really don't go together," said KPN spokeswoman Victorina de Boer.

Most Dutch children cycle to school and back, in a country with plentiful bike lanes. But in 2015, one in five cycling accidents involving young people was caused by using a phone. Such accidents cost 12 youngsters their lives and 441 were injured in 2015, according to the Dutch Traffic Safety association.

It's not just about texting. A recent study by KPN among 12 to 18 year olds also found they are easily distracted while cycling by vibrations from incoming messages on WhatsApp, Snapchat and Instagram.

The traffic body has joined forces with KPN to develop the special system which unlocks the bike and at the same time communicates with the cyclist's phone.

Instead of unlocking the bicycle with a key -- the usual method in The Netherlands in a bid to stop thefts -- the cyclist uses a mobile app which then sends a signal to KPN once the bike is unlocked.

Once in the saddle, internet and phone signal links are cut, except for the 112 emergency number.

"Once the app is used to lock up the bike again then the cyclist is able to use his phone properly again," said de Boer, adding the system was being tested this summer and would eventually go on sale for about 100 euros first for Android phones.