Integrating Autonomous Buses into Public Transport Systems: An Assessment of Potential Traffic & Environmental Impacts

The concept of autonomous buses (ABs) is emerging as a transformative innovation in public transport, with the potential to enhance safety and ensure service reliability. Their ability to reshape urban transport patterns has become a main focus of research. This study investigates the impact of two AB driving behaviours, defensive and aggressive, on real public transport networks in Istanbul. Traffic efficiency, safety, and emissions were evaluated using the open-source traffic simulation platform SUMO. Two demand levels (off-peak and peak hours), varying penetration rates, and two management strategies (dedicated lanes and mixed traffic) were analysed to assess their effects. Results show that AB-defensive behaviour increases average time loss, whereas AB-aggressive strategies reduce it as penetration rises. In dedicated lane scenarios, full deployment of AB-aggressive driving reduces time loss by up to 4.0 times in off-peak and 2.4 times in peak hours compared to the baseline, while AB-defensive driving increases it by up to 3.6 times. Regarding safety, at a 100% AB-defensive rate, conflicts decrease by 94% and 84% in off-peak and peak hours, respectively, whereas AB-aggressive behaviour yields smaller reductions (63% and 28%). CO and HC emissions under dedicated lane scenarios decline by as much as 57%, with aggressive driving providing the greatest benefits. The promising effects of ABs are most evident in dedicated lanes, while in mixed traffic, especially at low penetration rates, their effectiveness declines. Overall, the findings highlight a trade-off between efficiency and safety, emphasizing the need for balanced deployment strategies.