Japanese car manufacturers will have to convince the public that letting go of the wheel in a self-driving car is safe, while also dealing with the biggest threat to the cars’ security: the humans using them.

Toyota, Nissan and Honda are intent on putting autonomous cars on highways — and also city roads for Nissan — by 2020, and the triumvirate of Japan’s auto industry were keen to stress the advances made so far at the recent Tokyo Motor Show.

Their stated goal — preventing deaths on the road — is laudable, but the technological arms race is also highly lucrative: consultancy firm AT Kearney has estimated the market for the self-driving car could be worth more than $566 billion by 2035.

Nissan chief executive Carlos Ghosn told reporters at the Tokyo show the company has high hopes the technology will save lives while altering car journeys forever.

“It compensates for human error, which causes more than 90 per cent of all car accidents.“As a result, time spent behind the wheel is safer, more efficient and more fun,” he said.

But Ghosn’s comments belie the work still to be done, as its engineers edge forward in steps rather than leaps.Google offers promises of a fully autonomous car, but these automakers are taking a more gradual approach, focusing on aspects such as self-parking and crash avoidance technology.

Functions such as emergency braking and speed-limiting devices that track the distance between vehicles already exist, but getting drivers to abandon the steering wheel completely is a harder sell.

“We must make sure our clients understand how the machine works,” said Nissan’s chief planning officer, Philippe Klein.

To instil confidence, the artificial intelligence that will power Nissan’s autonomous cars will mirror the driver’s driving style as closely as possible, while “ironing out any bad habits”, the automaker said.

Obtaining the trust of drivers is crucial, as without it “we cannot move forward”, said Moritaka Yoshida, a Toyota executive.

And even if the user of a self-driving car is convinced of its superior safety, other road users need to feel secure sharing the tarmac.

Manufacturers are experimenting with icons or written messages appearing on wind-shields, warning sounds, and in one case a light-strip along the length of the car whose colour and intensity would alter in different situations.

Intersections present a particular challenge, said Melissa Cefkin, who is based at Nissan’s Silicon Valley research centre.

“Sometimes drivers communicate between themselves and with pedestrians or cyclists directly, by swapping looks, with a hand gesture, or even verbally,” she said.

“Sometimes it’s interpretative: we look for signals while judging the vehicle’s speed and movements.” The tiny pointers that motorists pick up from one another are not yet within the reach of the technology. “Currently, the machine isn’t capable of grasping all the subtlety of these clues,” Cefkin said.

To better understand them, Nissan is undertaking the immense task of studying thousands of intersection scenarios in an attempt to identify cultural patterns by country or context.