Use of reasoning maps in evaluation of transport alternatives: inclusion of uncertainty and “I Don’t Know”: demonstration of a method

Selection of a transport alternative is usually a messy process. The traditional approaches consider the relationships as either deterministic or probabilistic, neither of which incorporates the degree of ignorance (i.e., “I don’t know” opinion). Further, different stakeholders seek to justify their preferences with reasoning that suits their agenda. This paper proposes and demonstrates a method that evaluates the validity of the reasoning process and derives the degrees of belief that stated goals are achieved. The paper demonstrates a ‘reasoning map’ method for evaluating transport alternatives, where the analysts accept and employ the notion of “I don’t know” about an issue. The reasoning map depicts the relational chains from the attributes of an action to the stated goals, and recognizes the notion of “I don’t know”. This paper uses the theory of evidence to account for ignorance; it calculates the propagation of uncertainties along the reasoning chains. The context chosen for this demonstration is the selection of a public transit mode, personal rapid transit, over Bus, in a commercial complex in Washington DC. The paper has a limited objective and is not a comprehensive evaluation of alternatives. It merely explains how to compute a numerical value for the strength of reasoning, how to deal with analyst’s notion of “I don’t know,” how to interpret the overall reliability of the reasoning process, how to measure the goal achievement of an alternative, and how to find the critical paths linking the planning options to goals. For use in planning practice, consultation of experts and affected citizens and aggregation of their views is needed to develop the reasoning maps.