More than half of fatbikes checked by police in Amsterdam in the last five months had been tinkered with to go faster than the maximum of 25kph.

Police carried out a total of 11 checks using a roller test bench. Of the 215 fatbikes, 117 were found to be doctored, mostly by installing a throttle to speed them up. Bike computers had also been manipulated, mobility platform Mobiliteit.nl reported.

Riders were given fines of €290 and 20 bikes were confiscated.

Doctored fatbikes, which are particularly popular among young teenagers, are increasing in number in the capital, prompting a national awareness campaign which will be launched by the infrastructure ministry next month. The campaign will focus on safety and the rules around fatbikes.

There are currently no age restrictions in place for fatbikes, and riders are not required to wear helmets or have a permit.

In 2022, just seven fatbike riders ended up in hospital emergency departments, but last year that had soared to 59. In the first four months of this year, there were 33 hospitalisations, a trend which if continued would take the full year total to around 100.

Research by VeiligheidNL has also shown that half the victims of accidents involving fatbikes are aged 10 to 14 and a quarter of them end up with head injuries. “These figures make it clear that urgent measures are needed to protect children and all road users,” the petition says.

Doctors, local authorities and traffic safety organisations have petitioned for an age limit of 12 but would have preferred 16. That is not legally possible because the fatbike is considered an electric bike and a minimum age of 16 would mean youngsters would also be excluded from riding a regular electric bike.

Amsterdam’s transport chief Melanie van der Horst, who also signed the petition, said it is time the government acted to stop the sale of doctored fatbikes. The council has been carrying out more controls but, Horst said, as long as they are still being sold the problem will continue.

“It’s too easy to hide behind the legal complexities,” Van der Horst said. “Children are ending up in intensive care and will be suffering the consequences for the rest of their lives.”

The campaign will help people to understand the rules around fatbikes, she said. “A doctored fatbike is not insured. But parents allow their children to ride them anyway.” Amsterdam schools have already received a letter from the council about this which they have sent on to pupils and parents.