Japan is far from the only place with autonomous vehicles on the roads, but its government has set acceleration of the technology as a key priority.

Last year, it became the first country in the world to allow a vehicle capable of taking full control in certain situations to operate on public roads.

The Honda car has "Level 3" autonomy, meaning it can take certain decisions alone, though a driver has to be ready to take the wheel in emergencies.

The government has changed the law to pave the way for increasingly advanced autonomous vehicles, and the ministry of economy, trade and industry (METI) has plans for 40 autonomous taxi test sites nationwide by 2025.

It's a policy driven by a serious problem: Japan's population is the oldest in the world, and the country is plagued by persistent labour shortages.

"In the cargo and transport sectors, drivers have become older and the shortage of human resources has become serious," a recent METI report said.

It also warned of "terrible traffic accidents caused by elderly drivers making operational errors".

With demand clear, local automakers have lined up to develop technologies.

Top-selling Toyota plans to run its e-Palette self-driving buses along dedicated roads in the smart city it is building at the foot of Mount Fuji.