Monday, 05 June 2023
A novel study undertaken by the University of Nottingham has found that, in the absence of someone in the driving seat, pedestrians trust certain visual prompts more than others when deciding whether to cross in front of an autonomous car.
The aim of the study was to understand how pedestrians respond naturally to self-driving vehicles with different External Human-Machine Interfaces (eHMIs) - visual displays positioned on the front of the vehicle. To do this, a car was driven around the university’s Park Campus over several days with a ‘ghost-driver’ concealed in the driver’s seat. A series of different designs projected onto the eHMI informed pedestrians of the car’s behaviour and intention – including expressive eyes and a face, accompanied by short text-based language such as “I have seen you” or “I am giving way”.
The eHMI was controlled by a team member sat in the back seat, while front and rear dash cam footage was collected to observe pedestrians’ reactions in real time. Additionally, researchers were placed at four crossing points to ask pedestrians to complete a short survey about their experience of the vehicle and its displays.
The 'ghost driver' was concealed in the car
David R. Large, Senior Research Fellow with the Human Factors Research Group at the University of Nottingham, said: “As part of the ServCity project, which created a blueprint infrastructure for autonomous vehicles in the UK, we wanted to explore how pedestrians would interact with a driverless car and developed this unique methodology to explore their reactions. We were keen to identify which designs invited the highest levels of trust by people wanting to cross the road."
We used three different levels of anthropomorphism; implicit, an LED strip designed to mimic an eye’s pupil, low, a vehicle centric icon and words such as ‘giving way’, and explicit, an expressive face and human-like language.
The study took place over several days, during which time 520 pedestrians interacted with the car, and 64 survey responses were collected. Several indicators from the dash cam footage were used to evaluate pedestrian’s crossing behaviour, including how long it took people to cross, how long they looked at the car and the number of times they glanced and/or gestured at the vehicle. This, combined with the survey results, gave researchers significant insights into people’s attitudes and behaviour in response to the different eHMI displays, and autonomous vehicles more generally.
We were pleased to see that the external HMI, was deemed to be an important factor by a substantial number of respondents when deciding whether or not to cross the road – an encouraging discovery for furthering this type of work.
Gary continued: “With regards to the displays, the explicit eyes eHMI not only captured the most visual attention, but it also received good ratings for trust and clarity as well as the highest preference, whereas the implicit LED strip was rated as less clear and invited lower ratings of trust.”
David added: “An interesting additional discovery was that pedestrians continued to use hand gestures, for example thanking the car, despite most survey respondents believing the car was genuinely driverless – showing that there is still an expectation of some kind of social element in these types of interaction.”
Moving forwards, the team will be looking to consider a broader range of vulnerable road users, such as cyclists and e-scooter users, and how they might naturally interact with a future autonomous vehicle. An additional recommendation is that studies also need to be undertaken over extended periods to understand how the public’s response to a driverless car might change over time.
ServCity, which came to an end earlier this year and was funded by the government’s £100m Intelligent Mobility Fund and administered by the Centre for Connected and Autonomous Vehicles (CCAV), was delivered by Innovate UK over the past three years.
Six project partners - the University of Nottingham, Nissan, Connected Places Catapult, TRL, Hitachi Europe and SBD Automotive - have been working to understand how to help cities get CAV ready and successfully incorporate autonomous vehicle technologies into complex urban environments to deliver “Robotaxi” style services and create a template for the type of infrastructure required to support these technologies.
For more information on the study, please click here.
Story credits
More information is available from David R Large, in the Faculty of Engineering at the University of Nottingham at david.r.large@nottingham.ac.uk or; Danielle Hall, Media Relations Manager for the Faculty of Engineering at the University of Nottingham, at danielle.hall@nottingham.ac.uk
About the Faculty of Engineering
Made up of six departments – Architecture and Built Environment, Chemical and Environmental Engineering, Civil Engineering, Electrical and Electronic Engineering, Mechanical, Materials and Manufacturing Engineering and Foundation Engineering and Physical Sciences – the university’s Faculty of Engineering is home to more than 5,600 students and 800 staff.
The faculty, which has educated engineers and architects for more than 140 years, was the first in the country to be accredited with an Athena SWAN Gold Award for excellence in advancing gender equality across higher education and research and is home to multiple state-of-the-art facilities, including the recently opened £40m Power Electronics and Machines Centre (PEMC).
With research at its heart, 21 research groups are undertaking pioneering projects for a sustainable future across several themes – including net zero transport, sustainable energies and the built environment, advanced manufacturing, and healthcare technologies – and has delivered a positive impact in more than 20 countries. Within those countries, the faculty’s research has supported 500 companies and three governments – that have changed their strategies as a result of its research – and has also directly created jobs for around 3,000 people across the world.
Notes to editors:
About the University of Nottingham
Ranked 32 in Europe and 16th in the UK by the QS World University Rankings: Europe 2024, the University of Nottingham is a founding member of the Russell Group of research-intensive universities. Studying at the University of Nottingham is a life-changing experience, and we pride ourselves on unlocking the potential of our students. We have a pioneering spirit, expressed in the vision of our founder Sir Jesse Boot, which has seen us lead the way in establishing campuses in China and Malaysia - part of a globally connected network of education, research and industrial engagement.
Nottingham was crowned Sports University of the Year by The Times and Sunday Times Good University Guide 2024 – the third time it has been given the honour since 2018 – and by the Daily Mail University Guide 2024.
The university is among the best universities in the UK for the strength of our research, positioned seventh for research power in the UK according to REF 2021. The birthplace of discoveries such as MRI and ibuprofen, our innovations transform lives and tackle global problems such as sustainable food supplies, ending modern slavery, developing greener transport, and reducing reliance on fossil fuels.
The university is a major employer and industry partner - locally and globally - and our graduates are the second most targeted by the UK's top employers, according to The Graduate Market in 2022 report by High Fliers Research.
We lead the Universities for Nottingham initiative, in partnership with Nottingham Trent University, a pioneering collaboration between the city’s two world-class institutions to improve levels of prosperity, opportunity, sustainability, health and wellbeing for residents in the city and region we are proud to call home.
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