The pioneering autonomous bus service in the Swiss city of Sion is entering a new phase. Thanks to intelligent traffic lights, the SmartShuttles will be able to cross junctions without the help of a driver.

Initially, the two bright-yellow driverless buses carried up to 11 passengers along a 1.5km (0.9 mile) route through the Old Town as part of an initiative launched in December 2015. The vehicle was the first of its kind in Switzerland and one of the first in the world to transport passengers using robotic technology instead of a driver.

On Monday, the city authorities announced the next innovation: the buses will now not only have to deal with a longer stretch with more traffic but also cross two streets. To enable them to do this safely, two intelligent traffic lights will be set up in the next few days.

Communication between the bus and the lights is via a wireless local area network (WLAN) that follows a new European standard being used in Switzerland for the first time. The shuttle receives a signal every second telling it when the lights change colour and the nature of the junction, allowing the bus to adjust its speed.

The next aim is to navigate roundabouts, with trials set to begin in the coming months.

Passengers can ride the buses for free and a human driver is always on board who can stop the bus if necessary. In 80% of cases when the human has to step in, it’s due to an illegally parked car.