As outlined in Chapter 2, HTA (Annett 2004) is primarily concerned with goals (an objective or end state) and their decomposition into sub-goals and the requisite physical and cognitive operations (Annett and Stanton 1998). HTA works by decomposing systems into a hierarchy of goals, sub-ordinate goals, operations and plans. It focusses on ‘what an operator . . . is required to do, in terms of actions and/ or cognitive processes to achieve a system goal’ (Kirwan and Ainsworth 1992, p. 1). Note that an ‘operator’, like an actor in CWA, may be a human or a technological operator (e.g. equipment, devices and interfaces). HTA outputs therefore specify the overall goal of a system, the sub-goals required to achieve this goal, the operations necessary to achieve each of the sub-goals specified and the plans that describe the ordering of sub-goals and operations.

HTA has previously been undertaken to describe the full driving task (see Walker et al. 2015). The analysis undertaken for the current project therefore focussed specifically on drivers’ interactions with rail level crossings.

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