Understanding Traffic Systems

Data Analysis and Presentation

Michael A.P. Taylor, Peter W. Bonsall

• Publisher: Routledge
• Year: 2017
• eBook ISBN: 9781351876858
• Topic: Technology & Engineering
• Subtopic: Geography
• Index: Geography

Road traffic and its impacts affect all aspects of modern life, leisure and industry, with safety, congestion and pollution being of greatest public concern. Transport planning increasingly emphasises travel demand management (TDM) and traffic calming - aided by dynamic, lower cost data from Intelligent Transport Systems (ITS) - to enable real time monitoring, control and traveller information. This second edition of a highly successful work has been fully updated since its first publication in 1996 to reflect developments in technology available to the traffic analyst and in the social, ecological and economic environment. New sections are included on shockwaves, data capture without surveys, traffic incidents, delay estimation, off-line use of on-line data, environmental sensitivity, and controlled crash tests. The authors introduce and demonstrate techniques with which the analyst, engineer or planner can examine traffic problems. The underlying theme is that proper understanding of traffic systems performance and traffic problems can only come from the intelligent processing, refinement, appraisal and evaluation of traffic data. Arranged in five parts, the book offers an integrated approach to tackling road traffic problems: ¢ How to gain information and understanding about traffic ¢ The theories of traffic flow ¢ The principles of good survey planning and management ¢ Specific types of traffic studies ¢ Analytical techniques for transforming raw data into useful information. Understanding Traffic Systems provides cogent insights into the techniques of traffic data collection and analysis, the application of traffic theory and the role of data in analysis and decision making. Its breadth and use of examples from several countries make it a useful reference text for students and researchers, as well as an essential tool for practising traffic engineers and planners.

Part E
Data Analysis and Modelling

15
From data to information

The results of traffic analysis must be transmitted to the user or client in a form that is understandable and efficient. Chapter 2 described the recent developments in database systems, spreadsheets and statistical packages that assist in this process. These tools are of considerable assistance in developing a picture of what a data set is trying to tell us. The important step is the transformation of data into information. To do this requires appropriate examination of the data, for which methods of data presentation, often graphically based, are used.

The first task in any analysis is to become familiar with the data. It is useful to have answers to questions such as: are there any outliers? Is the distribution of the data symmetric? Do data values accumulate in the middle or at the end? Are any values repeated? Answers to these questions can often be obtained by having a look at the data. Data may be viewed through the astute use of tables (Section 15.1), but one of the most powerful methods is the construction of diagrams (Section 15.2). This forms the basis of Exploratory Data Analysis (EDA, see Section 15.3).

The correct analytical procedure with any data set is to undertake EDA and then move into statistical analysis. EDA can also be used throughout the statistical analysis process to enrich understanding and interpretation (see Chapter 17). Modem methods of interactive data analysis allow analysts the opportunity to have many different views of the data, quickly. Then follows the use of descriptive statistics (Section 15.4).

15.1 Tables

The tabular form of presentation is a common and useful first step in data analysis. The simplest table is just a simple listing of the data. The listing of vehicle speeds in Table 15.1 is an example of this form of presentation. These speeds are those from the data set presented in Appendix B.

Table 15.1 Vehicle speeds (km/h) in residential streets

The unsystematic manner in which the data are presented in Table 15.1 makes it difficult to gain insights into the character of the data. A better view may be gained by arranging the data in some manner. The ordering of the data from the lowest to the highest value is presented in Table 15.2. This table provides more insight. It shows the extremes of the data and provides an indication of where the data tend to group together.

Table 15.2 Table of speeds (km/h) sorted in increasing order

These tables present information on one variable and are, therefore, referred to as one-dimensional tables. One-dimensional tables can be divided into the following components: the table number, the title or caption, the (column) headings, the stub (or left-hand column – a vertical listing of categories about which data are given in the other columns of the table) and, if necessary, the source. The table number, title/caption, column headings, stub and other columns of data make up the body of the table. Table 15.3 is an example of a simple one-dimensional table with the components marked.

Table 15.3 One-dimensional table

Two-way classification tables can be obtained by subdividing the stub. Two-way classifications are sometimes referred to as cross-tabulations. They are possibly the most common analytical method in the social sciences. The first step in the construction of cross-classification tables is to determine the primary emphasis. The data with the primary emphasis should be place...

Table of contents

• Cover
• Half Title
• Title
• Copyright
• Contents
• List of figures
• List of tables
• Preface
• Acknowledgements
• Part A: INTRODUCTION
• Part B: BASIC TRAFFIC THEORY
• Part C: DATA CAPTURE
• Part D: TRAFFIC STUDIES
• Part E: DATA ANALYSIS AND MODELLING
• Appendix A: Statistical tables
• Appendix B: Database of vehicle speeds on residential streets
• References
• Index