This study examines pedestrian walking-side bias in America. We recorded the walking behavior of 430 pedestrian groups and analyzed the left-vs-right passing response around either a stationary obstacle or other oncoming pedestrians. Past research indicates about two-thirds of American pedestrian’s favor walking on the right side of a centrally located inanimate object. We test if this lateral bias is larger for interactions between bypassing people in larger group sizes. We tested two principal hypotheses: H1: Overall, pedestrians will exhibit a right-side passing bias, and H2: The magnitude of the right-side passing bias will increase as a function of group size. Our findings confirm H1: We found a reliable right-side pedestrian bias when pedestrians pass either an inanimate object or other people, a percentage that is similar to past findings. We also confirmed H2: when passing people but not obstacles. When individuals of groups pass other people, biases are additive, with the right-side lateral walking bias increasing by about 10% per additional pedestrian, reaching a ceiling of about 95% rightward paths for groups of five or more. In general, the right-side lateral walking-bias appears to be a prototypical example of a socially trained natural regularity that is readily modified by situational contexts. Findings from this study confirm that small individual biases accumulate into larger biases in groups, a principle that likely has wide ranging generalizability relevant to both the design of locomotive spaces as well as group dynamics in other more abstract socio-relational domains such as political views and prejudice.