Compensatory behavior for mental workload induced by freeway destination signs.

Objective: Exit ramps are accident-prone areas of freeways. One of the reasons for this is the information overload induced by destination signs, which makes them challenging to recognize and may even result in tension or mistakes. This study examined the cognitive workload that destination signs place on drivers and the compensatory behavior they use to counteract the additional workload.

Methods: Forty-five subjects were recruited to conduct a simulated driving experiment. Four destination signs with varying information levels were used to load mental workload as independent variables. Workload indicators (such as the NASA-TLX questionnaire, heart rate variability and eye movements) and compensatory behavior metrics (such as speed, distance headway, time headway and the increased cognitive time due to deceleration) were collected and analyzed through a mixed design analysis of variance.

Results: The results show that destination signs with different levels of information produced various cognitive workloads. Drivers' subjective workload increased significantly with an increase in sign information; however, the heart rate variability indicators did not significantly differ due to the drivers' compensatory strategy in the cognition process. The principal compensating strategy found was the longitudinal deceleration; as the speed dropped, the distance headway and time headway were significantly increased. Although professional drivers demonstrated a significantly greater speed differential during deceleration than nonprofessional drivers, the alternative safety indicators did not show statistical differences. Additionally, driving experience had no significant impact on the increased cognitive time of compensatory strategies.

Conclusions: On the one hand, the effort invested by drivers increased with the workload. On the other hand, when the workload exceeded a particular degree, compensatory driving behavior was triggered, which in turn reduced the workload. There was no discernible difference in the effectiveness of the compensatory strategies employed by professional drivers and nonprofessional drivers under complex destination signs. The findings could provide safety considerations for the design of traffic signs.