New Modeling Approach for Mixed-Traffic Streams with Nonmotorized Vehicles

Mixed-traffic streams that contain motorized and nonmotorized vehicles are becoming more common in urban areas. These streams contain standard vehicle types such as private cars, buses, and trucks, as well as nonstandard vehicles such as bicycles, motorcycles, and other vehicular forms. Models suitable for analysis of such streams hardly exist, and most available models are limited in scope and effectiveness. Analysis of mixed streams that use traditional approaches has achieved limited success and has involved much recalibration effort and significant model modifications. Effective analysis of these streams therefore inevitably requires new models to be developed that use different approaches. Aspects of a model developed specifically for mixed streams are presented. This model covers different vehicle types, including nonmotorized ones, and allows for some special behaviors, such as seepage to fronts of queues by two-wheeled vehicles and simultaneous use of two lanes. In addition to normal car-following rules, the model incorporates lateral movement with a gradual lane change maneuver (as opposed to an instantaneous one), the decisions of which are governed by fuzzy logic rules. The model was calibrated and tested with data from Nairobi, Kenya, and its predictions were found to be in close agreement with the field data. In addition to its being a normal traffic management tool, the model makes a significant contribution to the study of the influence of nonstandard vehicle types or behavior on traffic performance.