Behavioural adaption of drivers of unequipped vehicles to short time headways observed in a vehicle platoon

Advanced driver assistance systems (ADAS) are increasingly present within modern vehicles, supporting the introduction of semi- and fully-automated driving situations. As a consequence, a mixed traffic situation is likely to emerge where vehicles equipped with different degrees of automated systems will interact with unequipped vehicle drivers (UVDs). Platoons of vehicles comprise a vision for future traffic and are designed to maintain small headways in order to have a beneficial effect on both energy consumption and traffic flow. The overarching aim of this work was to investigate whether the presence of automated vehicle platoons will impact UVDs’ car-following behaviour. This required understanding in which conditions behavioural adaptation of UVDs can possibly emerge. Therefore, four studies were conducted using a car simulator whereby participants drove behind a lead vehicle in the vicinity of automated platoons of vehicles exhibiting different headway characteristics. Further external factors were varied across the different simulator studies. In summary, when drivers were motivated by instructions and not impeded by keeping track of a lead vehicle, expected changes in behaviour were noticed: reductions in mean THW, minimum THW, amount of time spent below a critical THW and the variation of lane position were observed when driving next to a platoon with short THWs. Contrarily, there was no significant effect of platoons’ headway when UVDs followed a lead vehicle as a result of congested traffic. It was interpreted that elements of the environment as well as driver’s cognitive state such as workload and motivation influenced the magnitude of the effects. Other factors are still unclear such as the influence of drivers’ personality and driving skills. More work is needed to understand fully the conditions that promote behavioural change. Beyond the scope presented here, further research is also needed to understand how increasing deployment of vehicles equipped with ADAS may affect driver behaviour across the wider vehicle fleet.