Published on GEOG 497C: Transportation GIS (https://www.e-education.psu.edu/geog497c)

Home > Lessons > Lesson 6: Linear Referencing Systems (LRS)

Lesson 6: Linear Referencing Systems (LRS)

Introduction & Learning Outcomes

What will we learn?

By the end of Lesson 6, you should be able to:

  • use ArcMap’s Linear Referencing Tools to construct routes from roadway centerline features;
  • calibrate the measures along a route based on actual measures made in the field;
  • describe the purpose and characteristics of a Straight Line Diagram (SLD);
  • create an SLD given event data along a route;
  • discuss the key functions of the American Association of State Highway and Transportation Officials (AASHTO);
  • describe some of the crash data reporting and analysis practices used by state DOTs;
  • share something you learned about one of your classmates and/or some ideas you discussed with a classmate about the content of this week’s lesson.

Assignments

Lesson 6 will take 1 week to complete. Please refer to Canvas for specific timeframes, submission instructions, and due dates.

To finish this lesson, you must complete the assignments listed below. The details for each assignment are provided in the referenced section and in Canvas.

Lesson 6 Assignments
Assignment No. Assignment Description Section Grade Component / Points
6-1 Complete a tutorial on using ESRI’s Linear Referencing Toolbox. 6.1 Lesson Topic / 25
6-2 Create a Straight Line Diagrams (SLD) from event data. 6.1 Lesson Topic / 10
6-3 Explore AASHTO and summarize one of their areas of activity. 6.2 Transportation Organizations / 15
6-4 Participate in a 1-on-1 video conference with a classmate and submit a summary of the conversation. 6.3 Class Participation / 15
6-5 Participate in this week’s webinar and submit a summary of what you learned. 6.4 Guest Webinar / 15
6-6 Review the background material for next week’s webinar and respond to some questions. 6.5 Guest Webinar / 10
6-7 Submit 3 - 5 questions for next week’s speaker. 6.5 Guest Webinar / 5

 

6.1 Linear Referencing Systems

Last week, we explored the purpose and components of an LRS. This week, you’ll have an opportunity to solidify your understanding by completing some hands-on exercises to create routes, calibrate linear measures along a route, and use dynamic segmentation to convert event tables into event features. You’ll also see how GIS software can be used to reduce the burden associated with the creation and management of an LRS and event data.

Assignment 6-1 (25 points)

Complete ESRI’s ArcMap tutorial [1] on linear referencing. Submit an M.S. Word document to Assignment 6-1 in Canvas which addresses the following questions:

  1. In Exercise 2, you created a route feature class from the “base_roads” feature class. Why do you think some of the features in the “base_roads” feature class are lacking a route identifier? (2 points)
  2. In Exercise 2, you created a route feature class. In creating the route, you defined how measures along the route would be determined. You had three choices: LENGTH, ONE_FIELD, and TWO_FIELDS. In your own words, describe how you think the measures along the route are determined using each of these methods. (3 points)
  3. How does a route feature class differ from a general linear feature class? (2 points)
  4. How does roadway grade (i.e., hills and valleys) affect the measures along a route? (2 points)
  5. In Exercise 3, you learned how to locate a point or range along a route using the "Find" tool. Using this tool, locate the section of route 20000264 between milepost 8.45 miles and 14.93 miles. Using the functions available on the context menu, which is visible when you right click the identified section roadway in the "Find" dialog, draw, label, and zoom to this location on the map. Include a screen shot of the resulting map display. (3 points)
  6. Include a screen shot of the ArcMap window, showing both the table of contents and the map displaying the accident and pavement events you created in Exercise 4. (3 points)
  7. In completing the tutorial on linear referencing, did you perform dynamic segmentation? If so, identify the exercise(s) and step(s) where dynamic segmentation took place. (2 points)
  8. What is the difference between an event table and an event layer? (2 points)
  9. Include a screen shot of the map you created at the end of Exercise 4 showing the injury accidents which occurred on roadways with a pavement rating below 50. (3 points)
  10. Briefly, compare and contrast the route calibration in Exercise 2 to that in Exercise 5. (3 points)

In the next major release of ArcMap, LRS functions will be removed from the product. In the past few years, ESRI has been looking to shift users instead to their new Roads and Highways product which is designed to provide a fuller featured set of tools for transportation organizations to manage their LRS and roadway event data. A 57-minute introduction to this tool [2] was provided at the 2013 ESRI users’ conference.

Straight Line Diagrams

Transportation organizations capture and maintain a large number of linearly referenced roadway events including:

  • Intersections
  • Bridges
  • Rail Crossings Locations
  • Legal Boundaries
  • Accidents
  • Signs
  • Speed Limits
  • Average Annual Daily Traffic (AADT)
  • Width of the Right of Way
  • Width of the Roadway Shoulders
  • Functional Class
  • Curves
  • Grades
  • Projects

Displaying more than a few of these on a single map can begin to clutter the map and make it difficult for the user to understand.

One tool which transportation organizations have used for many years to visualize road attribute information is a Straight Line Diagram (SLD). In an SLD, a roadway section of interest is presented as a straight line along with various roadway attributes or events. Often these roadway attributes are maintained by separate groups within the transportation organization, and sometimes they are linearly referenced using different LRMs. An SLD brings many attributes together with a uniform referencing method to facilitate visualization of the data and the potential identification of relationships between different data elements.

The specific layout of SLDs varies from one organization to another. One common layout for an SLD includes three components: a map component, a schematic component, and an attribute component. The map component often appears at the top of the SLD and presents the alignment of the route of interest. The schematic component, also sometimes referred to as a stick diagram, presents the route as a straight line and can incorporate roadway features such as intersections, bridges, ramp entrances and exits and legal boundaries. The attribute component includes roadway event data presented along the same horizontal axis. Linear events such as speed limit are displayed as a series of horizontal bars with the extent of each bar corresponding to the region over which the attribute has a constant value. Point events are displayed as point symbols positioned according to their location along the route.

Example layout of SLD with speed limits from 55 to 40, AADT, and where the crashes took place.
Figure 1 - Example SLD Layout

Historically, SLDs were manually created and assembled into books for reference across the organization. Given the effort required to generate SLDs in this manner, the books often reflected data which was somewhat dated. Today, most SLDs are created dynamically from current event data using sophisticated GIS software applications.

As an example, the Massachusetts Department of Transportation uses a web-based tool called Massachusetts Route Log [3] to generate Straight Line Diagrams (SLDs). Here is an example SLD generated from this application for a portion of State Route 9.

Massachusetts Route Log tool displaying a portion of State Route 9.
Figure 2 - Massachusetts Route Log
Credit: MassDOT

Vermont’s Agency of Transportation (VTrans) has a similar SLD tool called VTrans Routelogs [4].

VTrans Route Log and Progress Chart
Figure 3 - VTrans Routelogs SLD
Credit: VTrans

Assignment 6-2 (10 points)

In this assignment, you will manually create an SLD for route 40001200 in Pitt County, North Carolina (the same county you worked with in Assignment 6-1). Submit the SLD as a M.S. Word document to Assignment 6-2 in Canvas. In your SLD, the positions of the events should be reasonable, but you can eyeball them. There is no need to be super accurate for the purposes of this assignment. The SLD should cover the portion of the route between milepost 8.5 and 11.5 and should include the following elements:

  1. The top portion of the SLD should include a map of the corresponding roadway alignment. (2 points)
  2. The central portion should present a linear representation of the route and all interesting routes. Only include routes maintained by the state. (2 points)
  3. The bottom portion of the diagram should display the following event data:
    1. Accident data (2 points)
      Use the accident event data from Assignment 6-1 and limit the accidents to those with injuries (Hint: Use an attribute query to see which accidents you’re interested in. Limit the route, measures, and number of injuries accordingly).
    2. Pavement rating data (see Assignment 6-1) (2 points)
    3. Speed limit data based on the following table: (2 points)
      Route Speed Limit Data
      Route Speed Limit Beginning MP Ending MP
      40001200 25 0.0 3.0
      40001200 55 3.0 9.0
      40001200 35 9.0 10.0
      40001200 55 10.0 15.0

Note: You can use whatever tools you’d like to create the diagram as long as it is submitted as an M.S. Word document. If you’d like, you can hand sketch the diagram. Assuming you don’t create the SLD directly in Word, you would insert an image or paste an image of your SLD into Word. My personal recommendation is to use a combination of M.S. PowerPoint with its drawing tools along with the Snipper utility in Windows.

 

6.2 Getting to Know a Transportation Organization

This week, you’ll take some time to get to know the American Association of State Highway and Transportation Officials (AASHTO). AASHTO is an association comprised of representatives from the state transportation agencies in all 50 states, the District of Columbia, and Puerto Rico. AASHTO seeks to promote transportation excellence and integration across the U.S. and to foster effective communication and cooperation between the state DOTs and the federal government. Founded over a century ago, it was originally named the American Association of State Highway Officials (AASHO). As with state DOTs, its focus has broadened over the years, and in 1973 it was renamed the American Association of State Highway and Transportation Officials (AASHTO) to reflect the fact that its scope of activities spans all modes of transportation.

AASHTO administers a variety of technical programs. A few of their more significant areas of activity are briefly discussed below.

Standards and Publications

AASHTO establishes technical standards and guidelines which are generally adhered to by the state DOTs in addition to many organizations outside the U.S. It has published many highly respected and widely used reference documents spanning a variety of transportation disciplines including the following:

  • A Policy on Geometric Design of Highways and Streets (also known as “The Green Book”)
  • The Highway Safety Manual (HSM)
  • Standard Specifications for Transportation Materials and Methods of Sampling and Testing
  • AASHTO LRFD Bridge Design Specifications.
  • Manual for Assessing Safety Hardware [5] (MASH)

AASHTOWare

AASHTO manages a program aimed at providing exceptional enterprise level software to transportation agencies. These products incorporate the experience and expertise of its member organizations and have been developed using pooled funds from state DOTs and the FHWA. The suite of software developed in this program is collectively known as AASHTOWare and its products span 5 core business areas:

  • Project
  • Bridge
  • Safety
  • Pavement
  • Right of Way

An overview of the AASHTOWare program is provided in this 7-minute video [6]. AASHTO also publishes a catalog of AASHTOWare products [7]. Many of the AASHTOWare software products incorporate varying levels of spatial technology. For example, the bridge products use the Google Maps API for spatial analysis and visualization.

Research

AASHTO is very active in the area of transportation research. A substantial portion of the research AASHTO promotes is carried out by the National Cooperative Highway Research Program (NCHRP).

AASHTO Materials Reference Laboratory

The AASHTO Materials Reference Laboratory [8] (AMRL) develops protocols for testing construction materials and accredits laboratories who test these materials. Many state DOTs require laboratories to be AMRL accredited before they will do business with them.

Centers of Excellence

AASHTO also operates the following three centers of excellence, each of which is designed to provide information and expertise in a specific area of transportation:

  • Center for Environmental Excellence
    This center focuses on environmental considerations associated with transportation.
  • National Operations Center of Excellence (NOCoE)
    This center focusing on topics relevant to transportation operations.
  • Build America Transportation Investment Center (BATIC) Institute
    This center focuses on funding and financing transportation projects.

Assignment 6-3

Spend some time exploring one of AASHTO’s specific programs or activities. It can be one of the areas I touched upon in the lesson or another area that catches your interest. Submit a 300-500 word summary of what you learned (as an M.S. Word document) to Assignment 6-3 in Canvas.

Review and Respond (15 points)
Criteria Ratings Pts
Followed Instructions Excellent: Student carefully followed all instructions for the assignment.
4.0 pts
Satisfactory: Student's submission exhibited some minor deviations from the instructions for the assignment.
2.5 pts
Poor: Student's submission exhibited major deviations from the instructions for the assignment.
1.0 pts
4.0 pts
Content Quality Excellent: Student's submittal fully addressed the topics of the assignment and demonstrated insight and thoughtful reflection on the part of the student.
7.0 pts
Satisfactory: Student's submittal partially addressed the topics of the assignment and demonstrated some insight and thoughtful reflection on the part of the student.
5.0 pts
Poor: Student's submittal did not address the topics of the assignment and demonstrated little or no insight or thoughtful reflection on the part of the student.
1.0 pts
7.0 pts
Writing Quality Excellent: Student’s writing was organized, clear, and concise and was free from spelling and grammatical errors.
4.0 pts
Satisfactory: Student’s writing exhibited some deficiencies in the area of organization, clarity, and conciseness and/or contained a few spelling or grammatical errors.
2.5 pts
Poor: Student’s writing exhibited major deficiencies in the area of organization, clarity, and conciseness and/or contained many spelling or grammatical errors.
1.0 pts
4.0 pts
Total Points: 15.0

 

6.3 Getting to Know Each Other

This week, you’ll have a one-on-one chat with one of your classmates (or me) as per the schedule you were provided in Week 1. The discussion should be at least 30 minutes in length. If it’s the first time you’ve chatted with each other, spend the majority of time getting to know each other. Otherwise, focus on discussing the lesson content.

Assignment 6-4 (15 points)

Submit a brief summary of the conversation (no more than 300 words) as an M.S. Word document to Assignment 6-4 in Canvas. The summary you’ll submit is an individual assignment and is not intended to be a joint activity. If it’s the first time you’ve spoken with each other, your summary should primarily address what you learned about each other (e.g., what do you have in common?). Otherwise, your summary should focus on ideas and insights about the lesson content which came out of the conversation.

One-On-One Rubric (15 points)
Criteria Ratings Pts
Followed Instructions Excellent: Student carefully followed all instructions for the assignment.
4.0 pts
Satisfactory: Student's submission exhibited some minor deviations from the instructions for the assignment.
2.5 pts
Poor: Student's submission exhibited major deviations from the instructions for the assignment.
1.0 pts
4.0 pts
Content Quality Excellent: Student's submittal reflected a conversation which was highly thoughtful and productive and provided substantial benefit in getting to know each other better and/or exploring lesson topics.
7.0 pts
Satisfactory: Student's submittal reflected a conversation which was somewhat thoughtful and productive and provided some limited benefit in getting to know each other better and/or exploring lesson topics.
5.0 pts
Poor: Student's submittal reflected a conversation which had little value in getting to know each other better and/or exploring lesson topics.
1.0 pts
7.0 pts
Writing Quality Excellent: Student’s writing was organized, clear, and concise and was free from spelling and grammatical errors.
4.0 pts
Satisfactory: Student’s writing exhibited some deficiencies in the area of organization, clarity, and conciseness and/or contained a few spelling or grammatical errors.
2.5 pts
Poor: Student’s writing exhibited major deficiencies in the area of organization, clarity, and conciseness and/or contained many spelling or grammatical errors.
1.0 pts
4.0 pts
Total Points: 15.0

 

6.4 Weekly Webinar

This week’s speaker is Mr. Bill Schuman. For details about Bill’s current role and background, refer to Lesson 5. For the specific date and time of the webinar, please refer to Canvas. While you are expected to attend the webinar live if at all possible, it is understood that, in some cases, work schedules and other conflicts may make it impossible to do so. If you will not be able to attend, please send me an e-mail ahead of time. I will make the recorded webinar available for you to review.

Assignment 6-5 (15 points)

After attending the webinar, prepare a brief write-up (300 – 500 words) summarizing the session and submit it in M.S. Word format to Assignment 6-5 in Canvas. In your summary, address the following:

  • What did you learn and/or find most interesting?
  • What was unclear in the presentation/discussion?
Webinar Rubric (15 points)
Criteria Ratings Pts
Followed Instructions Excellent: Student carefully followed all instructions for the assignment.
4.0 pts
Satisfactory: Student's submission exhibited some minor deviations from the instructions for the assignment.
2.5 pts
Poor: Student's submission exhibited major deviations from the instructions for the assignment.
1.0 pts
4.0 pts
Content Quality Excellent: The student's submittal demonstrated that the student paid close attention during the webinar and carefully reflected on the key topics which were covered.
7.0 pts
Satisfactory: The student's submittal demonstrated that the student was somewhat attentive during the webinar and engaged in limited reflection on the key topics which were covered.
4.0 pts
Poor: The student's submittal provided little or no evidence that the student paid careful attention during the webinar or reflected on the topics which were covered.
1.0 pts
7.0 pts
Writing Quality Excellent: Student’s writing was organized, clear, and concise and was free from spelling and grammatical errors.
4.0 pts
Satisfactory: Student’s writing exhibited some deficiencies in the area of organization, clarity, and conciseness and/or contained a few spelling or grammatical errors.
2.5 pts
Poor: Student’s writing exhibited major deficiencies in the area of organization, clarity, and conciseness and/or contained many spelling or grammatical errors.
1.0 pts
4.0 pts
Total Points: 15.0

 

6.5 Next Week's Webinar

Speaker

Next week, our guest speaker will be Mr. Jeff Roecker. Jeff graduated from Penn State with a degree in Geography and joined PennDOT in 2008. Jeff plays a lead role in the Department's Crash Data Analysis and Retrieval Tool (CDART), and he is the project manager for PennDOT's Strategic Highway Safety Plan (SHSP).

Crash Data Collection

FHWA requires all states to maintain a database of crashes in order to support the analysis of crash locations. There is variation from state to state on how they define reportable crashes, how they collect the information and how readily they share the information. Many states publish annual summaries of crash data for the prior year and also provide trending information for various crash statistics. The Pennsylvania Department of Transportation (PennDOT) publishes an annual report entitled Crash Facts and Statistics. The 2015 version of this publication can be found here [9].

Crash data is important to state DOTs for a number of reasons. First, without this data, an agency doesn’t know if things are improving. Second, this data can offer clues to where safety improvement or countermeasures are most needed. Crash patterns can also be used to help law enforcement design initiatives associated with seat belt usage and checkpoints for impaired drivers.

Law enforcement officials are generally responsible for reporting crashes. In Pennsylvania, the Commonwealth of Pennsylvania Police Officers Crash Report Manual provides law enforcement agencies instructions on reporting crash data including definitions of which types of crashes are reportable to PennDOT. The police use a multipage form (AA 500 [10]) to report crash data. The form captures extensive information about the crash including the location, all vehicles and individuals involved in the crash, the number and nature of any injuries, weather and road conditions at the time of the crash, a diagram of the crash and statements from any witnesses. PennDOT also provides a detailed reference document [11] for completing the form.

PennDOT also has a web based system called the Crash Reporting System (CRS) which provides an electronic alternative to submitting crash data. A user’s guide for the system can be found here [12]. CRS is also used by PennDOT to review and validate all data which is automatically retrieved from paper forms which are received from law enforcement agencies. Any meaningful analysis of crash data requires that the data is accurate and complete.

Crash Analysis

State DOTs use crash data to identify locations where there are unusually high crash rates and also to determine measures which will likely lower these crash rates. One of the most useful types of crash analysis, which is used by many state DOTs, is a spatial technique known as cluster or hot spot determination. This type of determination is done using GIS software by stepping along each route and identifying sections of roadway which meet the definition of a crash cluster based on established parameter settings for the analysis.

In Pennsylvania, crash data submitted by law enforcement agencies electronically via CRS or the AA500 paper form, are processed and stored in a system known as the Crash Data Access and Retrieval Tool (CDART). CDART is a geospatial application which allows PennDOT to perform a variety of crash analyses including crash cluster analyses. It performs two basic types of crash cluster analysis. The first is a standard cluster analysis where each road is considered separately. The second is an intersection based cluster which examines the number of crashes which occur on all associated roads within a certain distance of the point of intersection. One of the other interesting analyses CDART performs is a “before and after” analysis which compares crash frequencies for a section of roadway before and after a safety improvement was implemented to determine its effectiveness. For each of the analyses CDART performs, the system allows the user to generate tabular or map based outputs. CDART is an internal tool to PennDOT and is not available for public use.

On May 30, 2013, Sharon Hawkins of the Arkansas DOT gave a 42-minute presentation on some of the GIS tools [13] they use to locate and analyze crashes. The presentation was part of the FHWA GIS in Transportation webinar series. The webinar provides an excellent perspective on the importance of GIS in collecting and analyzing crash data. Many states have gone through a similar evolution and set of problems in their efforts to manage and utilize crash data to improve highway safety.

Assignment 6-6 (10 points)

Review the Pennsylvania Police Crash Reporting form and associated guidance for reporting crashes and watch the Arkansas DOT’s May 2013 webinar on GIS tools they’ve used to locate crashes and analyze crash data. Address the questions listed below and submit your responses as an M.S. Word document to Assignment 6-6 in Canvas.

  1. How does Pennsylvania define a reportable crash? (1 point)
  2. What are some types of information a police officer can provide to locate a crash in Pennsylvania? (2 points)
  3. Why is it important for PennDOT (or any state DOT) to ultimately associate a crash with a specific location along a roadway as opposed to simply capturing the coordinates of the crash? (2 points)
  4. In Arkansas’s evolution of locating crashes, they deployed GPS units to the police to help them accurately locate a crash. What was one of the problems they identified after providing these units to the police? (1 point)
  5. What are some of the GIS tools Arkansas DOT has rolled out to help law enforcement locate crashes? (2 points)
  6. How does Arkansas DOT benefit from law enforcement’s ability to more accurately locate crashes? (2 points)

Assignment 6-7 (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 6-7 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

 

6.6 Summary of Lesson 6

In this lesson, we explored how GIS tools can be used to help maintain an LRS and event data.  We also examined dynamic segmentation, a process used to convert event data into event features, and some very useful diagrams known as Straight Line Diagrams (SLDs).

Our transportation organization of the week was AASHTO. We reviewed some of the important roles AASHTO plays in establishing policy, producing important guidance documents, conducting and promoting research and in creating exceptional software products for a number of functional areas in transportation.

In our weekly webinar, we had the chance to interact with Mr. Bill Schuman, Sr. Vice President of Project Delivery for Transcend Spatial Solutions, and benefit from his expertise and many years of experience in the area of LRS.

In preparation for next week’s webinar, we looked at how state DOTs collect and analyze crash data.

Finally, you had the opportunity to get to know one of your classmates a little better and share some of your ideas and questions about this week’s lesson materials.

Questions and Comments

If there is anything in the Lesson 6 materials about which you would like to ask a question or provide a comment, submit a posting to the Lesson 6 Questions and Comments discussion in Canvas. Also, review others’ postings to this discussion and respond if you have something to offer or if you are able to help.

 


Source URL: https://www.e-education.psu.edu/geog497c/node/517

Links
[1] http://desktop.arcgis.com/en/arcmap/10.4/manage-data/linear-referencing/an-overview-of-the-linear-referencing-tutorial.htm
[2] http://www.esri.com/videos/watch?videoid=2679&channelid=LegacyVideo&isLegacy=true&title=esri-roads-and-highways---an-introduction
[3] http://services.massdot.state.ma.us/mrla/RouteSelection.htm
[4] http://vtransmaps.vermont.gov/routelogs/map.htm
[5] http://safety.fhwa.dot.gov/roadway_dept/policy_guide/road_hardware/ctrmeasures/mash/
[6] http://www.youtube.com/watch?v=iF7htviiQNI&t=33s
[7] http://www.aashtoware.org/Documents/FY2017_Catalog-Final.pdf
[8] http://www.amrl.net/
[9] http://www.penndot.gov/TravelInPA/Safety/Documents/2015_CFB_linked.pdf
[10] https://www.reportbeam.com/RBInfo30/states/pdfsamples/PennsylvaniaSample.pdf
[11] https://www.dot6.state.pa.us/crsapp/html/AA500RefManual/whnjs.htm
[12] http://www.penndot.gov/TravelInPA/Safety/Documents/WebManual.pdf
[13] http://connectdot.connectsolutions.com/p2xo4mimbcs/?launcher=false&fcsContent=true&pbMode=normal