Properties of pedestrians walking in line without density constraint

This article deals with the experimental study of pedestrian behaviors in some situations of one-dimensional traffic. Participants were preorganized in a line and asked to walk either in a straight line with a fast or slow leader or to form a circle. The originality of our experimental protocol compared to previous ones on similar situations is to have left the condition of density free. While the observed density results from individual decisions in the line case, both density and velocity have to be collectively chosen in the case of circle formation. Our major findings are the following. In the case of circle formations, we observe that the resulting velocity is very stable among realizations, as if collective decision was playing the role of an average. For line flows with a slow leader, the same operating point close to the jamming transition is chosen as in previous experiments where it was not velocity but density that was imposed. In the less constrained line experiments, although participants could choose comfortable headways, they rather stuck to short headways requiring a faster adaption-a fact that could come from a "social pressure from behind" and had previously been observed only at high densities. This could be due to the uncertainty and individual responsibility that stem in less constrained situations. Our results open avenues for future research, as they show that the walking values preferred by humans in following tasks depend on more factors than previously considered.