Comparing the usefulness of a connected environment during mandatory and discretionary lane-changings

Lane-changing manoeuvre is one of the risky manoeuvres performed by drivers either to reach the planned destination (i.e., mandatory lane-changing; MLC) or to achieve better driving conditions (i.e., discretionary lane-changing; DLC). Essentially both lane-changing types require the driver to acquire surrounding traffic information for efficient and safe lane- changing decisions. However, this does not discount the fact that both these lane-changings are fundamentally different from each other as the urgency of lane-changing is much higher during MLC compared to DLC. A connected environment promises to assist during the lane-changing decision-making process, but the differential effectiveness (or usefulness) of a connected environment for these two lane-changing types remains unexplored due to the novelty of a connected environment and the consequent scarcity of data. To fill this research gap, this study collected lane-changing data from 78 participants who performed MLC and DLC in the CARRS-Q Advanced Driving Simulator. Participants were asked to drive in three randomised driving conditions: baseline condition (without driving aids), connected environment with perfect communication, and connected environment with communication delay. While surrogate measures of safety are analysed and compared using descriptive statistics, a hybrid framework of data mining and classical statistical modelling is employed to examine the usefulness of the connected environment for two lane-changing types. We find that the crash risk associated with MLC is significantly reduced in the connected environment driving conditions compared to that of DLC. Results also reveal that the probability of engaging in a hard-braking event decreases for both the lane-changing types during the connected environment driving conditions, but a higher decrease in magnitude is found for MLC. Age and gender-related differential impact have been observed where young and male drivers have a higher possibility of engaging in a hard-braking event when driving without driving aids, but the connected environment reduces such risk. This study concludes that the usefulness (or effectiveness) of the connected environment is a function of the urgency of a task, which is evidently higher during MLC, thus providing the maximum advantage during MLC