Effects of Cell Phone Conversation on the First Driver Response to a Stopped Lead Vehicle

Abstract

Despite ample research on the effects of cell phone conversations on driving, the effects of such conversations on the looming threshold for an immediate hazard are not known. Prior research on the looming threshold for an immediate hazard in the absence of cell phone conversation indicated that the rate of optical expansion at threshold was .006 radians per second. We measured the rate of optical expansion and headway distance at first driving input when participants encountered a stopped lead vehicle while completing a car-following task. Half of them concurrently completed the Last Letter Task, a cognitive task that emulates a cell phone conversation. When compared to the second, third, and fourth scenario exposures to the stopped lead vehicle, the participant’s response on the first scenario exposure occurred when the lead vehicle’s optical expansion rate was relatively smaller and headway distance was larger. However, this effect of scenario exposure occurred only when drivers were engaged in a cell phone conversation. Additionally, participants started to initiate a response when the rate of optical expansion was much lower than the looming threshold reported in previous research. Our results indicate that the first driver input, as operationalized in the current study, does not indicate when drivers first perceive an immediate hazard.