Techniques for Transit Data Visualisation

One of our goals in this research is to take advantage of AVL capabilities by collecting a huge amount of transit vehicle operational data to improve the analysis of displaying transit data graphically and pictorially. Visualisation is a process of transforming data into a visual form, enabling the user to better understand and extract information. Visualisation gained widespread currency in the mid-1980s when for the first time computer graphics was linked to supercomputer processing, particularly in scientific contexts (Michael, et al, 2004). Visualisation is a very broad term and its styles vary enormously with context. In transit industries, visualisation encompasses many definitions and uses, it plays a key role in displaying raw transit data as well as operations performance data that contains detailed and accurate information. Visualisation is not only valuable in identifying potential problems; it also helps to improve service reliability.

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Many transit agencies have found that visualising transit data is necessary for planning, management and analysis purposes. (Langendorf, R., 2010) Argues that the ability to understand complex phenomena often requires investigation from multiple viewpoints using a variety of data sources and that visualisation can serve to enhance communication among the participants in the problem solving process. Transit performance monitoring applications can readily embrace visualisation techniques and concepts, with beneficial results. Transit data can be visualised through static or dynamic frameworks using tables, maps, data plots and other graphical outputs which provide users and operators with a variety of information in easy to understand ways. (Wei F. et al, 2010) provide ways to summarize and visualise bus route operations data using colour counter diagrams and a dynamic interactive bus monitoring visualisation framework based on the Google Maps platform. Figure (3-5) shows on-time performance data using a box-plot graph. Each box-plot shows the range of the schedule adherence (actual departure time minus scheduled departure time) values for each stop during the time of measurements.

Figure 3-5 On-time performance data using a box-plot graph (Source: Wei F. et al, 2010)

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Figure (3-5) illustrates the use of a box-plot graph to visualise on-time performance data. The names of bus stops are represented on the x-axis while the departure times in seconds are represented on the y-axis. Various visual tools ranging from graphical views to 3D-animation and virtual reality have been used by transit agencies for better managing and the planning of transit operations. Information graphics in the form of charts are typically used to convey information about a single attribute measured at regular time intervals. Most map-based transit applications focus on a particular aspect of a transit service occurring within a geographic space at a single point in time. Transit operators need to visualise their transit fleet performance to monitor and detect any negative service symptoms such as schedule/headway deviation and bus bunching. (Thomas J, 2007) developed new analysis and visualisation techniques for presenting important information to decision makers. The author stated that the visualisation of bus transit performance information was not exploited enough. Efforts to make use of transit data have often been hampered by problems with data collection and post processing as well as budget limitations.

Visualisation techniques such as time-distance diagrams (K., Kuhn, 2011) have been used as a tool to visualise transit performance information. Time-distance diagrams are used to show transit vehicle locations as a function of time. Mapping of quantities as shown in Figure (3-6) is one commonly used method in the transit sector for visualising transit data.

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Figure 3-6 The Mapping of Quantities method for transit data visualisation (Source: Thomas J., 2007)

This method basically renders the quantities of an attribute by varying its symbology; either by colour-coding graduated symbols or by using proportional symbols or dot density. As can see in Figure (3-6) dwell time values for each bus stop are rendered by different sized circles.

Linear referencing (Figure 3-7) is another method used in the transit sector. It is used in the area of asset management and transit vehicle performance monitoring purposes. In linear referencing visulasation technique the locations of features are identified by a relative measure along a linear element.

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Figure 3-7 Linear referencing method for transit data visualisation (Source: Thomas J., 2007)

As can see in Figure (3-7) bus stop locations are identified by on-time performance values along the bus route.

3-D visualisation is also applicable to visualise transit data (Thomas, J., 2007). It can be used to analyse and display transit performance that cannot be realized in two dimensions alone. In general, visualisation techniques do not create new data, but rather allow attributes inherent in the data to be expressed intuitively. Visualisation techniques can improve the perceived quality of transit data and ease information extraction. For dynamic visualisation, a web-based interface can be considered as one of the main tool which has been used for visualising transit data. With such a tool, transit users are able to see routes, stops and moving buses on digital maps simultaneously. Zoom and pan controls, as well as satellite imagery, allow users to apply their personal knowledge to achieve faster and more accurate transit results. Web-based applications are generally interactive, so users can quickly navigate to a geographic area of interest, (e.g., place of work or home) or view only a specific bus route. (Ricardo H., 2009) developed a web-based application for the public transport system of Calgary, Canada. The application was developed to explore alternative

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techniques of schedule dissemination. In this application, Google maps were used to visualise transit information. Figure (3-8) shows a screenshot of the Calgary (Canada) public transport system.

Figure 3-8 Screenshot of Calgary (Canada) public transport system (Source: Ricardo H., 2009)

As we can see in Figure (3-8) which represents a public interface of Calgary Canada public transport system transit vehicle are depicted on transit map and on the right side input box tools is provided for faster transit data retrieval and allow users to select and add particular buses they are interested in. These tools called location search and bus lists. To enhance and improve the usability of a public transport system through visualisation, (B, Ferris, et al., 2011) developed a web-based OneBusAway transport application. The Authors described the application as a set of transit tools focusing on providing real-time information to transit riders in the Puget Sound region of Washington State. Figure (3-9) shows a screenshot of the OneBusAway transport system (Source: B.Ferris. et al., 2010)

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Figure 3-9 A screenshot of OneBusAway transport system (Source: B.Ferris. et al., 2010)