United States Department of Transportation
i
Task Decomposition Model for Dispatchers in Dynanic Scheduling of Demand Responsive Transit Systems
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2000-06-01
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[PDF-1.40 MB]
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Abstract:Since the passage of ADA, the demand for paratransit service is steadily increasing. Paratransit companies are relying on computer automation to streamline dispatch operations, increase productivity and reduce operator stress and error. Little research has been performed to understand the task complexity of dispatchers interacting with their computer systems.
This research was conducted to provide an in-depth understanding of the task complexities and requirements for paratransit dispatchers. To achieve this, we organized, modeled, and analyzed a complete paratransit dispatching task sequence for a Los Angeles area paratransit service provider. Extensive field observations, video recordings, and expert dispatcher interviews were conducted to sketch out a dispatcher?s task sequence model during a high workload period. Using Hierarchical Task Analysis (HTA), this skeleton model was further refined into a comprehensive decision hierarchy (decision tree). The HTA was further extended to capture the sequence of activities between two dispatchers, a paratransit van dispatcher and a lead dispatcher, in the same operation room. The results of this analysis have shown that the dispatchers undergo intensive and complex cognitive processes. Their task performance seems to be heavily influenced by the type of software interface they use. We found HTA to be a useful tool to model these interactions. The sequential decision tree format of HTA also shows promise for training system design. In particular, we recommend the use of this model for part-task training for entry-level dispatchers.
In addition to task modeling, we further analyzed the design of the software interfaces used in this operation from a human factors standpoint: a DOS-based screen design and a Windows-based graphical user interface design. The DOS-based design had the advantage of information simplicity. However, this design produced long information scanning and navigation time, potentially long learning curve and screen design inconsistency. The Windows-based system had the advantage of a more natural spatial and iconic representation, well-designed popup menus and cursor sensitive information display. The most significant disadvantage of this design was a very long system lag time (e.g., it sometimes took up to 30 seconds for the system to respond to an input). This problem alone was the reason why the dispatchers did not use this system during high-demand periods. Other disadvantages were high-density clutter at low zoom level, layout inconsistency between zooms, inappropriate color-coding and no direct (active) driver interaction with the system in case of GPS failure. We believe that dispatch software developers should be encouraged to look into a more natural and quick response software interfaces. In general, we recommend a redesign of the current system based on the principles of user-centered interface design.
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