  The logistics of urban areas are becoming more sophisticated due to the fast
city population growth. The stakeholders are faced with the challenges of the
dynamic complexity of city logistics(CL) systems characterized by the
uncertainty effect together with the freight vehicle emissions causing
pollution. In this conceptual paper, we present a research methodology for the
environmental sustainability of CL systems that can be attained by effective
stakeholders' collaboration under non-chaotic situations and the presumption of
the human levity tendency. We propose the mathematical axioms of the
uncertainty effect while putting forward the notion of condition effectors, and
how to assign hypothetical values to them. Finally, we employ a spider network
and causal loop diagram to investigate the system's elements and their behavior
over time.
