GIS for Transportation: Principles, Data and Applications

5.5 Next Week's Webinar



Next week, our guest speaker will be Mr. Bill Schuman. Bill is the Sr. Vice President of Project Delivery for Transcend Spatial Solutions. His responsibilities include project manager oversight, providing subject matter expertise for road inventory, asset management, linear referencing systems (LRS) and road data models, business operations, and guiding the company’s strategic direction. He has over 28 years of transportation and GIS experience. He is a recognized LRS and transportation data expert and has worked with state and local governments on IT strategic plans, spatially enabled database and data warehousing projects, LRS design and implementation projects, and many custom data maintenance and data presentation applications.

Bill holds a B.S. in Civil Engineering from the University of Wyoming and is a GIS Professional.

Linear Referencing Systems (LRSs)

Transportation agencies capture a wide variety of information about their roadways in addition to information about assets or occurrences along their roadways. Some of these attributes relate to a specific location (e.g., crashes) while other attributes relate to a section of roadway (e.g., speed limit). Collectively, these point or linear attributes are referred to as events.

The crash takes place in a 35mph speed limit area and in between the speed limit areas of 55 mph.
Figure 7 - Crash and Speed Limit Events

The large number of events which need to be associated with the geometry of the roadway creates a challenge due to the fact that they often change values at different locations. For example, the locations where speed limit changes occur generally doesn’t correspond to the points where changes in payment type, the number of lanes, or the condition of the roadway occur.

The amount lanes, material, speed, and quality. Asphalt has fair and good quality in speeds ranging from 35 to 55, whereas concrete has poor quality in the 45 mph range and good at 35 and 55.
Figure 8 - Route Events
Credit: ESRI

Consequently, if we were to attempt to segment the roadway in such a way to ensure all attributes were constant over the length of each segment we would wind up with a highly segmented roadway. Alternatively, if we were to create a separate linear feature class for each roadway attribute we would have a large number of feature classes which would need to be maintained. One solution to this problem is to separate the events data from the route geometry and maintain them in separate tables which relate to the route geometry according to the route name and a linear measure (for point events) or pair of measures (for linear events) which indicate the location of the event along the route.

There are many different ways one can locate an event along a route. For example, an event could be located according to its distance along the route in miles from the county line. Alternatively, the distance could be measured from the beginning of the route or some other established marker or datum. These different approaches are referred to as Linear Referencing Methods (LRMs).

Given the relationship between the events in the events table and the route features, GIS software can dynamically create feature classes for any specific event or combination of events. This process is known as dynamic segmentation. The standard set of geoprocessing tools can then be applied to these dynamically generated features just as they can be applied to a persistent feature class.

The entire system which an organization uses to allow for the separation of event data and dynamic generation of feature classes is known as a Linear Referencing System (LRS). LRSs have been used extensively with road networks but they are applicable to other types of linear networks as well including pipelines and hydrologic networks.

Assignment 5-6 (10 points)

Read the article “A Comprehensive Process for Linear Referencing” (URISA Journal Vol. 19, No. 2, 2007). The article begins on page 41. After you have read the article, submit an M.S. Word document to Assignment 5-6 in Canvas which answers the following questions:

  1. According to the authors, what four elements comprise a LRS? (2 points)
  2. Is an address an example of an LRM? Why or why not? (2 points)
  3. How does Richardson’s decision to maintain a “quasi-carriageway” representation of their street network impact the number of event records they need to maintain? (2 points)
  4. What do the authors mean when they say “the GIS data is the datum”? (2 points)
  5. Why are certain geoprocessing tools like routing and geocoding lost when a road network is linearly referenced? (2 points)

Assignment 5-7 (5 points)

After reviewing the background material for next week’s webinar and the biography for next week’s speaker, come up with 3-5 questions which are clearly stated and are relevant to the webinar topics. Submit the questions to Assignment 5-7 in Canvas.

Webinar Questions Rubric (5 points)
Criteria Ratings Points
Question Quality
Excellent: Questions were clearly worded, demonstrated a thorough review of the background material and thoughtful reflection and insight on the part of the student.
5.0 pts
Satisfactory: Questions were somewhat clear, demonstrated some review of the background material and some reflection and insight on the part of the student.
3.0 pts
Poor: Questions were unclear and/or demonstrated little or no review of the background material and/or demonstrated little or no reflection and insight on the part of the student.
1.0 pts
5.0 pts
Total Points: 5.0