Driverless cars could be fitted with external displays to help them communicate with vulnerable road users such as runners and cyclists.

Researchers at the University of Glasgow and KAIST in South Korea have used augmented reality tech to explore how runners’ behaviour differs from walkers’ when crossing roads and junctions. They found that runners are much more likely to take risks when negotiating traffic than walkers and often took less time to process the road conditions around them. On several occasions, they were ‘struck’ by virtual vehicles in the team’s simulated road tests.

The team suggested that displays of lights on the exteriors of cars called external human-machine interfaces, or eHMIs, could enable them to communicate their intentions more quickly and effectively.

These displays could provide non-verbal cues, such as the waves, eye movements and deceleration that human drivers currently use to show people around them how they intend to proceed. The researchers suggest an eHMI design called DualBeam, which uses new types of lights on the vehicle to help runners make swift but well-informed crossing decisions.

Professor Stephen Brewster, a researcher on the study, said: “We’ve been working for several years now on developing eHMIs which could help self-driving cars share the roads safely with vulnerable road users such as cyclists. In doing so, we realised that there’s been very little research into how runners might expect to interact with driverless cars.

“Clearly, it will be increasingly important to ensure that runners and autonomous vehicles [AVs] can share the roads safely in the years to come. We were keen to explore how self-driving cars could use eHMIs to speak the language of runners as well as bike riders to help maximise road safety.”

To test how walkers and runners might interact and communicate with self-driving cars, the team used an augmented reality headset to mix real-world conditions with a life-size simulated AV. The virtual environment enabled them to safely test how self-driving cars might behave around runners and walkers in the future.

The study’s 24 participants went outdoors wearing the headset, which showed them a virtual urban environment overlaid on the real world. The participants either walked or ran towards a junction with a simulated AV approaching.

The simulated car had either no safety features displayed on its exterior, or one of two eHMIs. One eHMI, a ring of lights around the car the team called a LightRing, showed green to indicate it was safe for the participant to continue or red to help them decide to stop. The other, a strip of animated cyan lights called CyanBand, swept the lights inward to show it is slowing and in the opposite direction to display acceleration. Sometimes the car stopped for the participants, and sometimes it did not.

The runners struggled to process the animation of the CyanBand lights in the limited time they had to focus on them while approaching the junction, while walkers found it useful. The LightRing display’s simple red-and-green colour scheme, on the other hand, was much more immediately legible to both groups.

The team proposes adapting its findings into a new eHMI called DualBeam, which places two rows of lights around each side of the car with colours chosen to be quickly understandable but avoiding the overfamiliarity of red and green. Instead, an amber ring would signify the car does not intend to yield, while a purple one would show that the car intends to let the runner pass safely.