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thumb_Designing Geodatabases for TransportationTransportation networks are highly spatial in nature and dependent upon a high level of planning in their design, operation and maintenance. Accordingly, they are well suited to geographical information systems (GIS) tools. While we tend to think of transport networks in a continuous fashion, primarily to get us from Point A to Point B, these networks are, in practice, made up of smaller segments, many of which are managed independently or in integrated fashion. J. Allison Butler provides readers with in depth knowledge about these networks and how they can be designed, planned and operated through the use of GIS tools.

 

 

Designing Geodatabases for Transportation

 

by
J. Allison Butler

ESRI Press

 

468 pages; 2008

ISBN-10: 158948164X – ISBN-13: 978-1589481640

Review by Jeff Thurston

 

 

 

 

 

J. Allison Butler is an experienced and accomplished transportation expert.  His work over 30 years has resulted in more than 75 publications. These have been oriented toward the built environment, transport planning and information systems related to safety and design. This book begins on the topics of transport databases, data models and Agile methods for design. The later invokes a separation of the geodatabase – the model, from the applications derived from the data. This should come as no surprise, since transportation data is well suited for numerous applications, dependent upon individual user needs.

The book begins by describing data models. It delves into the functioning of databases and how they operate. Relational types are discussed and the author expands upon conceptual data models, logical and physical data models. A description of the relationship of Unified Modeling Language (UML) is provided. “Although it is common to do so, it is really a bit of a stretch and mismatch to use UML steady-state diagrams as a data model,” Butler says.  He argues that diagrams do not reflect the variety of uses, and flexibility, inherent in the data through graphics. As one might imagine, all of us should remain alert to the limitations of graphics when working with dynamically changing, and capable of changing, spatial information.

In chapter 3 the book describes geodatabases. This is a topic that receives consistent coverage in most ESRI Press books given that ArcGIS software is obviously used as the GIS software for the work supporting most of the books. The geodatabase framework is outlined, data dictionary discussed along with other topics like attribute domains, valid value tables, subtypes, relationship classes, origin and destination tables, nomalization and tracking events. Two additional geodatabase classes, relevant ot transport GIS are included – the junction feature class and edge feature classes as part of geometric networks. A turn feature class is also mentioned.  To describe these data tables, examples based on pavement condition, bus tracking and traffic counts are included.

Best practices in transportation geodatabase design are included in chapter 4. Centerlines, intersections, realignment, segmentation, mapping, census, multiple street names, emergency and designing a pavement management system are provided. The graphics in the book are exceptionally helpful in providing an understanding of detailed ‘linear facility geometry’ – roadwork. The author moves between GIS theory and application type, back and forth, guiding the reader to understand how scale, intersections and junctions impact abstraction. He speaks about added ‘intelligence’ within the data model, as a matter of design. Realignment methodology is discussed, and although a relationship to surveying is made, it is not too detailed, instead focusing again on the design elements of road building. Details are included for application types such as limited-access highways, limited access-highway ramps, roads and streets as well as various types of intersections.

A common difficult every city seems to have is related to naming of steets along with left and right addressing. Rightfully, the author describes streets that have multiple names (I live on one in Berlin as a matter of fact). The issue of emergency response to street names is provided and enhanced 3-digit emergency phone response is included. 

Many of us do not think about pavement management systems when driving our cars. However, GIS provides a methodology for managing street repair and surfaces. Rating, depth, inspection, type and segments are just a few of the pieces of information such a system relies upon. The segmentation of a road network for this purpose requires some consideration and planning, since, the size of the database itself can expand based upon the system management design. This in turn impacts performance. But ultimately it amounts to ensuring the road network is adequately managed and maintained in a system that enables consistent management – a term that is identified as ‘Project Involvement’ within the database, defining the relationshiop of many projects to individual segments. A considerable amount of attention includes traffic analysis zones (TAZs). These involve travel demand models and pathfinding.

A chapter on data editing provides the reader with an overall understanding of editing needs from a transportation perspective. This discussion expands into a wider understanding of editing across a network where many users are involved and each performing different operations on the same dataset. Short and long transaction editing are included. Versioning is discussed for those interested or needing to update default versions or rollback to previous versions. An example based on code ratings for editing purposes is provided and described. Similarly, the management of the data dictionary itself is also included. The relationship of these operations to wider Service Oriented Architecture (SOA) is also included.

Dynamic segmentation receives considerable attention within the book. A ‘traversal’, for example, is a route composed of part or all of other routes. However, the author outlines advanced dynamic segmentation functions. A short description about issues related to signage is not something many of us often think about. But, a GIS databases for transportation purposes would include signage and eahc of those signs must be located at the correct location and facing the correct way. This sounds simple enough, but consideration with respect to road curves and slopes is also included in optimally locating signage. Alternatively, segementation may also involve several overlays and include different numbers of lanes, speeds and lane types for a given section(s) of roadway.  The book describes how a GIS data table can be designed to accomodate all of these variables.

Traffic monitoring systems are useful for not only understanding the dynamics of traffic flow- the patterns, but also provide a means to management the underlying infrastructure that enables them. Automated traffic recorders (ATR) enable the determination of numbers of vehicles and types. The book describes these devices in detail.

An extensive example of a traffic monitoring system is modeled, included event factors and seasonal information. Readers will learn about the UNETRANS data model which was developed at the University of California and funded by ESRI. That model includes design factors and some of the philosophy about how and why the model was developed. The work of this model forms the bulk of detailed modeling for transportation within the book. Rail systems are also included. Material also includes considerations for crash modeling along transport corridors.

This book includes information about inventory control and the calibration of infrastructure along transport corridors. It describes the measurement and calibration of devices along road segments – noting the requirement that accurate geometry lends itself to better measurements. Essentially it includes provision for the use of new instruments, many of which are more capable of providing higher accuracy, into the data model as time progresses. Transit systems and the development of tolls and charging across schedules is also included within the model and discussed. The book does describe waterway networks and outlines the inclusion of data relating to water levels, beacons, lighting and other infrastructure along these channels. A similar discussion follows in the last chapter for railroad networks.

In summary this book is an excellent overview of transportation networks and the many factors that describe their operation. The author’s experience and knowledge are clearly revealed within the book through their expression in the level of detail within the transportation data modelling. This book does not read solely on the basis of a transportation study. Instead, the author links GIS to transport with significant understanding of GIS software, database knowledge and transport design factors. The graphics in this book are very clear. Even the smallest tables can be read, and that is evidenced in the many data tables.

This book would serve undergraduate students studying transportation very well. It provides a well-rounded discussion of transport elements and design for roads, rail and waterways. At the same time, it provides experienced transportation professionals who may not have GIS knowledge or who are beginning to integrate GIS with transportation data with a thorough understanding of how the two come together and where they can begin to design their own GIS transport operations and networks using these tools.

Jeff Thurston is Co-founder Vector1 Media and editor, Europe, Middle East, Africa and Russia for V1 Magazine and V1 Energy Magazine.

 

 

 

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