Ambulances to jam car radios in Sweden

Ambulances in Stockholm are testing a system that interrupts in-car audio systems to warn drivers that they need to get through.

The solution was developed by students at the KTH Royal Institute of Technology in the city.

It broadcasts a voice warning, while a text message also appears in the radio display.

It uses an FM radio signal to jam drivers' speakers and stop music playing.

It will only be able to alert cars that have their radios turned on. It can also interrupt CDs and music connected via Bluetooth.

The radio transmission is sent from the emergency vehicle to nearby FM tuners that are equipped with RDS, a communications protocol for embedding small amounts of digital information in FM radio broadcasts. It is most commonly used to display the station or song title.

"Often drivers have only a few seconds to react and give way to emergency vehicles," said Mikael Erneberg, a KTH student who worked on the system.

"The optimal warning time is at least 10 to 15 seconds."

Loud music can prevent sirens from being heard and, according to the students, accidents involving motorists who have not heard emergency vehicles are on the rise.

"We want to catch motorists' attention at an early stage, and mitigate stress that impairs road safety," said Mr Erneberg.

"It fulfils three functions: improving accessibility for first responders, improving road safety and make the working environment in transport better for vulnerable professions," said Mr Erneberg.

The city will begin testing the system in a limited number of ambulances and fire engines, with plans to expand across the country later this year.

The warning system can work out how far in advance messages need to be heard depending on the speed of traffic.