The safety of diabetic drivers has become a popular topic very recently, as accumulating evidence in the developed countries has suggested that diabetes is related to increased driving risks. However, the studies were mostly conducted in the developed western nations, and focus on the evaluation of driving safety among type 1 diabetes. The studies of type 2 diabetes which occupied the vast majority in Asia were few. Besides, most of them paid attention to the mechanism of driving with diabetes during hypoglycemia. Driving during non-hypoglycemia attracts little attention. Last but not the least, no studies put forward the improvement for type 2 diabetes from the aspect of system design. To fill the gaps, we discussed the factors of driving safety for type 2 diabetes, starting from the chronic impairment in cognition and diabetic self-management. Then we went further to find the optimal pedal design specific for drivers with diabetic peripheral nerve lesions.
The Study One (A) investigate the influence of type 2 diabetes on driving behavior in focus group. The interviews showed that few patients pay attention to the relationship between the abnormal blood glucose (BG) level and driving safety. And the symptoms of abnormal BG varies with the individual. The ability to be aware of abnormal BG is different for everyone. The interviewers tend to make decisions for driving based on the symptoms. They report anxiety, fatigue, distraction, blurred vision, slow reaction, numb, insomnia impaired driving behavior at different levels.
The Study One (B) conducted surveys among the drivers with type 2 diabetes, and collected disease information (the duration of diabetes, glycosylated hemoglobin, complications, hypoglycemia experiences), cognitive failure, subjective ratings on diabetic peripheral neuropathy (DPN), the brief knowledge about diabetes and the self-care activities, as well as the driving information. We found that the hypoglycemia experience, diabetic knowledge, self-care activities, cognitive failure and the subjective ratings on DPN are effective predictors of driving behavior. Those people with diabetes who have more hypoglycemia experiences, be lack of diabetic knowledge, fewer self-care activities, more cognitive failures and higher DPN rating scores are at a higher risk of driving. Also, we should pay attention to the mid-aged male drivers with diabetes, for their lack of knowledge, regardless of self-care activities and more risky driving behavior.
In Study Two (A), we conducted the experiments by driving simulator to figure out whether developing type 2 diabetes may impair driving skill. We compared the difference of driving performance between patients and their matched controls through the car-following in curvatures task and the pedestrian-vehicle-conflict tasks.The results showed that the patients' group has a longer brake reaction time, shorter minimum time-to-collision, and larger centerline deviation. Besides, as the road curve become sharper, as well as the leading car triggered a more emergency brake, the driving performance declined faster in patients group. It follows that there are impairments in driving skills of patients with type 2 diabetes.
In Study Two (B), we discussed the reason for their impairments in driving skills. We recruited patients with type 2 diabetes and their healthy controls to perform a
simulated car-following task and finish behavioral tests of haptic perception, visual search, attention span and working memory abilities during non-hypoglycemia. They also reported their hypoglycemia experience and perceived driving skills. We found that such between-group differences in driving performance could be fully mediated by haptic perception, visual search ability, attention span and working memory capacity but not by hypoglycemia experience. Regarding the effect sizes of the mediation, the visual search ability played the most critical role, and then followed the attention span, working memory, and the haptic perception.
In Study Three (A) we discussed how to improve the design of brake pedal to reduce the influence of DPN on braking behavior. The Study Four (A) tried reducing the brake reaction time by using pedals with different layout design. Three groups of participants were recruited: the patients with type 2 diabetes and high Semmes-Weinstein monofilaments Examination (SWME) scores (15), the patients with type 2 diabetes and low SWME scores (15), and the healthy controls (29). All participants finished a series of vehicle-pedestrian conflict tasks in a driving simulator using nine different types of pedal layouts. These layouts varied in accelerator-brake lateral distance and brake-pedal width. The results showed that patients with type 2 diabetes and high SWME scores had longer brake reaction time (BRT) and shorter minimum distance-to-collision (DTC) as compared to other two groups. Also, under the condition of the shortest accelerator-brake lateral distance (45mm), patients with high SWME scores showed substantially reduced BRT and increased minimum DTC without any increase in pedal errors.
The Study Three (B) investigated the differences in the performance of force control and force maintain tasks. It is a 2 (groups: healthy controls group and patients group)*2 (force feedback)*3(the amplitude of force)一design. The results showed that:there is a significant interaction effect on the amplitude of force and the groups. The patients' group had worse performance when triggering the small amplitude of force,compared with the healthy controls group. Based on this findings, we suggested that a smaller force transfer rate may benefit the patients' group to get a better pedal control.
This initial study provides original and first-hand evidence demonstrating that
the middle-aged male drivers with type 2 diabetes have deteriorated driving performance, but they are unaware of it. We will also discuss the possible measures to identify people of the highest risk and improve their safety awareness by using the findings of the current study.