## 4 Discussion
### Effects of eHMI Information Contents, Gap Size and Speed on Gap Acceptance  
The findings reveal typical gap acceptance patterns [54]: pedestrians are more likely to accept larger temporal gaps, with the probability of crossing increasing significantly as gap size expands. Additionally, higher vehicle speeds significantly increase the likelihood of crossing. This might be due to the fact that, under higher speed conditions, the spatial distance between the vehicle and the pedestrian is greater for the same temporal gap size. Pedestrians tend to perceive this larger spatial distance as a safer situation, thereby increasing the likelihood of crossing. This observation aligns with the previously identified 'farther and safer' perceptual bias [55]. This perceptual bias is further reflected in the interaction between vehicle speed and gap size when pedestrians encounter TVs without eHMI under partial eHMI penetration conditions (Partial-TVs), where larger gaps at higher speeds result in a steeper increase in crossing probability. However, this interaction effect did not reach statistical significance under full eHMI penetration conditions or when pedestrians encountered AVs with eHMI under partial penetration conditions (Partial-AVs). This discrepancy may potentially be due to the presence of eHMI. Prior studies suggest that eHMI presence enhances pedestrians' sensitivity to gap size variations, similar to the effect of vehicle speed [11; 14]. The six eHMI configurations in this study may have heightened pedestrians' sensitivity to the interaction between eHMI and gap size, thereby diminishing the effect of vehicle speed and gap size interaction. \begin{table}
\begin{tabular}{p{142.3 pt} p{142.3 pt} p{142.3 pt}} \hline \hline
**eHMI Information Content** & **Fros** & **Cons** \\ \hline \multirow{4}{*}{Medium-risk} & eHMI indicating medium crossing risk serves as a warning. Given that the medium crossing risk phase is the most uncertain, it is essential to provide a clear alert. P20 & An eHMI indicating only medium crossing risk, carries a high degree of ambiguity-leaving it unclear whether it signals permission to cross or a warning not to cross. \\ \cline{2-3}  & An eHMI indicating high crossing risk provides a crucial warning against crossing, thereby enhancing pedestrian safety during road-crossing decisions. & (a) When eHMI indicates high crossing risk, the vehicle is already very close to the pedestrian, requiring an urgent response. (b) eHMI indicating high crossing risk, along with its corresponding warning code, induces a sense of fear in pedestrians. \\ \hline \multirow{4}{*}{Low-medium risk} & (a) Information timing that offers sufficient response time. (b) Providing continuous information, which increases the level of certainty. & In the low-medium eHMI condition, the medium risk information is unnecessary, as pedestrians would cross during the low risk period. \\ \cline{2-3}  & The medium risk signal could serve as a transitional cue, helping participants anticipate the high-risk signal. & eHMI indicating medium and high crossing risk, along with its corresponding warning code, induces a sense of anxiety in pedestrians. \\ \cline{2-3}  & Partial. P16, P24 & Full. P1, P5, P10 \\ \hline \multirow{4}{*}{Low-medium-high risk} & (a) Provides continuous information, enhancing certainty. (b) Analogous to traffic lights, a familiar signal system for pedestrians. & (a) Mentally demanding. (b) Rapid information changes lead to misjudgments. (c) High-risk information may be redundant, as medium-risk signals suffice. \\ \cline{1-1} \cline{2-3}  & Full. P3, P6, P10, P11 & Full. PS \\ \cline{1-1} \cline{2-3}  & Partial. P13, P20, P22, P23 & Partial. P14, P16, P19 \\ \hline \hline \end{tabular}
\end{table} 
Table 12: Cont. Under both Full- and Partial-AVs conditions, the interaction between eHMI information content and gap size was significant.