Chapter 4 - Executive Judgment, Delphi, Scenario Writing, and Survey Methods

Abstract

This chapter deals with the employment of qualitative methods for the forecast of transport demand. First, the executive judgment method is presented, more specifically the assumptions, characteristics, scientific background, and applications for transport demand problems. Next comes the Delphi method, which examines a transport problem by exploiting, analyzing, and synthesizing the anonymous judgments of a group of experts in successive rounds (from two up to five), during which the experts are informed about other experts' views and can change and improve their previous statement. Simple statistical methods, such as the degree of consensus and Kendall's coefficient of concordance, are analyzed and permit the evaluation of the validity of the Delphi method. Several cases of application of the Delphi method for transport problems are presented. Assessment of future demand can also be achieved with the construction of alternative scenarios, which describe plausible or desired situations as well as processes that can lead to future levels of transport demand. Various types of scenarios (projective, perspective, etc.) are explored, and statistical methods to check inconsistencies within the parameters of each scenario are attempted. Applications of the method for assessing the effects of factors of the internal and external environment on mobility and transport demand are presented. Survey methods based on a questionnaire are used to accurately monitor and detect present and plausible future characteristics, attitudes, and trends of demand. The various methods of sampling (random, stratified, cluster) are studied. The relationship between the sample explored and the population surveyed, the margin of error, the confidence level, and the required number of questionnaires are identified and quantified. The appropriate design of a questionnaire is suggested. The use of many types of scales to quantify respondents' answers is investigated. Stated preference and revealed preference methods are analyzed, and the theoretical background, characteristics, and areas of application of each one are conceptualized. Characteristics and representative types of questionnaires are given for each sector of transport: airports, airlines, railways, sustainable urban mobility, and sea transport.