Driverless cars have moved a step closer to becoming a reality on the roads of Europe after 17 countries signed a joint declaration regarding a coordinated cross-border approach to autonomous vehicle testing.

Driverless taxis are already used on the streets of more than two dozen cities across China and the United States, but differing national policies have so far held up progress in Europe.

Now, seven years behind schedule, it looks like things could soon be moving after transport ministers from countries including France, Germany, Italy, Poland, and Sweden put their signatures to a document establishing a common testing framework.

Autonomous vehicle expert Herve de Treglode said progress had been held up in Europe by the existence of a developed public transport network and also by regulatory issues, such as the current requirement for a non-intervening "safety driver" to be on board. But he also said he believed robotaxis could be in commercial use as early as next year.

"London is ready, Madrid too," he said. "In the US and China, they don't do six months of testing and then stop. They roll out in a neighborhood, remove the safety driver, then launch commercial service with massive investments."

China's pioneering work in autonomous taxis is making inroads in cities across Europe.

Apollo Go, which is part of the Baidu group, will be part of trials in London later this year, and WeRide is involved in services in Madrid, with another Chinese technology company, Momenta, being part of trials in the German city of Munich.

In April, Uber launched a commercial robotaxi service in the Croatian capital Zagreb, involving Chinese company Pony.ai, which is also close to launching a trial in Luxembourg.

Pony.ai's co-founder and CEO Peng Jun studied at Stanford and Tsinghua universities before working at Baidu and Google and then founding the company in 2016.

He said Luxembourg's "forward-looking regulatory environment provides a strong foundation for autonomous mobility testing in Europe".

"Together with Bolt and Stellantis, we look forward to validating Pony.ai's technology in local traffic scenarios and supporting the responsible development of autonomous mobility across the region," he said.

Markus Villig, founder and CEO of the ride-hailing company Bolt, told the website Taxi Point it was inevitable Europe would follow the lead of other regions where driverless vehicles are a part of everyday life.

"Autonomous mobility technology is already transforming transportation around the world, and as the only independent, European-founded ride-hailing platform competing globally, we want to be at the forefront of scaling this revolutionary technology in Europe," he said. "We welcome Luxembourg's progressive approach to testing this technology and we are excited to work closely with our European partner Stellantis, and global software leader Pony.ai to launch further pilots in the future."