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A simulation model of mixed traffic flow at non-signalised intersections, based on the Shared Space approach

The objective of this thesis project is to analyze the traffic behaviour that the Shared Space approach assumes to enforce in a traffic space designed according to its principles, and to determine the impact of this behaviour on traffic performance and safety, isolated from location-specific elements. This is done by means of a new conceptual model and an implementation of it in a simulation model. Shared Space is, if anything, a road design process, with a vision on the functions of public spaces and on the role of stakeholders in designing them. Traffic behaviour and traffic control measures should not severely restrict other functions of public spaces. Shared Space distinguishes between social behaviour and traffic behaviour. Social behaviour could sometimes overrule established traffic rules. This shift may lead to a reduced level of experienced safety. This is supposed to help to improve the objective safety levels, based on (reverse) risk compensation. Analyzing Shared Space traffic demands a simulation model to be applicable to an intersection, accommodate different modalities, include the road and the movements on it, model the impact of the road environment and contain a form of conscious decision-making. In scientific literature, a large number of appropriate models can be found, such as gap-acceptance models, conflict-point models and social force models. The conceptual model emphasises the dynamic relation between two fundamental traffic processes, negotiation and movement. Negotiation between road users will determine their accelerations, and subsequently their speeds and positions. All modalities are involved in the negotiation process, assuming sufficient communication to clarify intentions. Every road user has two behavioural variables: an initiative factor and a politeness factor. The initiative factor determines whether the road user, during negotiating, would like to take precedence even if it does not have priority. The politeness factor impacts whether the road user will offer or accept that the other road user will proceed despite its not having priority. Road users have fixed paths consisting of curve points connected by line elements. In the negotiation process, it is calculated whether the trajectories of any two road users will be in conflict within a certain time horizon. If so, both road users can have alternative acceleration patterns, leading to alternative trajectories, which can also be tested for potential conflicts. The two behavioural variables initiative and politeness have an impact on the range and sequence of considered potential accelerations. The simulation model, a combination of object-oriented and procedural elements, is implemented in Matlab. The program generates a graphical user interface, which can be used to adjust input variables and visualise output data. The model's face validity has been analyzed on the basis of simulations of eight traffic situations, concerning following behaviour, conflict handling and the impact of initiative and politeness. The simulation results are largely as expected for moderate traffic demand. The simulation model is applied to four cases in order to determine the impact of varying initiative and politeness shares on two indicators for an intersection's performance and safety: the average speed and the Time Exposed to critical TTC (TET) value. Increased initiative and politeness do not lead to a higher average speed or a lower aggregated TET value. There is a significant correlation for individual road users between taking initiative and experiencing a higher average speed and a lower TET value. For politeness, such a correlation was not found. The Shared Space approach can be modelled as a concept and implemented as a simulation program for heterogeneous traffic on a generic intersection. The simulation results do not back up the assumption that the approach would have an impact on traffic performance and safety.