  When streets are designed according to the shared space principle, road user
are encouraged to interact spontaneously with each other for negotiating the
space. These interaction mechanisms do not follow clearly defined traffic rules
but rather psychological and social principles related to aspects of safety,
comfort and time pressure. However, these principles are hard to capture and to
quantify, thus making it difficult to simulate the behavior of road users. This
work investigates traffic conflict situations between pedestrians and motorized
vehicles, with the main objective to formulate a discrete choice model for the
identification of the proper conflict solving strategy. A shared space street
in Hamburg, Germany, with high pedestrian volumes is used as a case study for
model formulation and calibration. Conflict situations are detected by an
automatic procedure of trajectory prediction and comparison. Standard evasive
actions are identified, both for pedestrians and vehicles, by observing
behavioral patterns. A set of potential parameters, which may affect the choice
of the evasive action, is formulated and tested for significance. These include
geometrical aspects, like distance and speed of the conflicting users, as well
as conflict-specific ones, like time to collision. A multinomial logit model is
finally calibrated and validated on real situations. The developed approach is
realistic and ready for implementation in motion models for shared space or any
other less organized traffic environment.
