Effects of Chinese Text Size on the In-Vehicle Text Legibility and Driver Distraction: A Simulator Study

The rising popularity of in-vehicle information systems (IVIS) in China highlights the significance of Chinese character displays. A key design factor for text-rich in-vehicle human–machine interfaces (HMI) is Chinese text size (CTS). However, the impact of CTS on text legibility and driver distraction has not been extensively explored. The present study launches a simulator experiment and adopts several one-way repeated-measure analyses of variance to identify the optimal CTS that maximizes text legibility while minimizing driver distraction. The findings indicate that both text legibility and driver distraction improved progressively as the CTS increased, reaching a specific size of seven millimeters, at which they approached asymptotes. Subjective measures were more sensitive than objective measures. The analysis showed no significant impact of CTS on task completion time, number of errors, total glance duration, mean speed, or lane position variation. However, larger CTS led to more frequent, shorter glances, whereas smaller CTS resulted in fewer, longer glances. CTS below seven millimeters was associated with lower subjective preference and a higher perceived workload. Therefore, it is recommended that a CTS of seven millimeters or larger be used to promote the design of driver-friendly in-vehicle HMI, control IVIS-related distractions, and enhance road safety in China.