GIS for Transportation: Principles, Data and Applications

7.1 Highway Safety


Highway safety is an important area of focus for state DOTs and the USDOT. There are few groups within the USDOT who are focused on improving highway safety. The first is the Office of Safety. The Office of Safety is comprised of two units. The Technologies Unit deals with safety-related highway design considerations and technologies which can be used to improve highway safety performance. The Programs Unit oversees federal and state safety programs. One of the key programs they administer is the Highway Safety Improvement Programs (HSIP). HSIP is a federal-aid program designed to provide funding to states for projects aimed at reducing fatalities and serious injuries on qualifying roadways. In 2016, the program will provide about 2.2 billion dollars to the states for safety projects.

Figure 1 - Highway Safety Improvement Program Funds
Fiscal Year 2016 2017 2018 2019 2020
Estimated Funding* $2.226 B $2.275 B $2.318 B $2.360 B $2.407 B

Reference: FHWA Website accessed 12/31/2016

To qualify for HSIP funds, a state is required to develop and maintain a Strategic Highway Safety Plan (SHSP). An SHSP is designed to guide the investment of funds to projects which have the greatest potential to reduce fatalities and serious injuries. To qualify for HSIP funds, states are also required to identify their priorities using a Data-Driven Safety Analysis (DDSA).

The second group within USDOT which is responsible for highway safety is the National Highway Traffic Safety Administration (NHTSA). NHTSA is an administration within USDOT whose mission is to reduce crash fatalities and injuries. We’ll take a close look at NHTSA later in this lesson.

At the end of Lesson 6, we learned how state DOTs collect and use crash data to identify areas of their roadway networks where there are unusually high crash rates. However, looking at crash data alone can be misleading and result in a less than optimal use of available state and federal dollars. To address this problem, AASHTO, in conjunction with the FHWA, developed the Highway Safety Manual (HSM), a document which many consider the definitive reference on highway safety. The HSM offers a comprehensive and balanced approach and set of tools which consider operations, the environment, and the cost of construction alongside safety considerations. A good overview of the HSM can be found here. The approaches provided in the HSM go beyond traditional approaches to identifying priority locations for safety improvements which rely solely on crash history data.

There are two fundamental problems associated with using crash data alone. First, crashes are statistical events and as such don’t occur at regular predictable intervals. Consequently, crash data alone can sometimes lead an agency to falsely identify sections of a roadway as high risk and, conversely, sometimes overlook a risky section. The second problem of looking solely at historic crash data is that it disregards the dependence of crash frequency on traffic. As traffic levels increase on a section of roadway due to changing travel patterns, crash rates can increase. To overcome these limitations, it is necessary to look not only at historic crash frequencies, but also at expected crash frequencies based on roadway characteristics and traffic data.

Tools have been developed which implement the approaches defined in the HSM. These include AASSHTO’s Safety Analyst and FHWA’s Interactive Highway Safety Design Model (IHSDM). However, states often lack much of the data required to effectively use these tools, such as horizontal and vertical curve data. Horizontal curves are roadway curves that turn to the left or right, and vertical curves are roadway peaks/hills and valleys. For my Capstone Project, I used roadway centerline data to extract horizontal curvature data from Pennsylvania’s roadways. I gave a lightning talk on the project at Penn State in November 2016 for GIS day. A link to the presentation is here (my presentation was just under 10 minutes in length and begins about 37 minutes into the recorded session).

Two model frameworks have been developed to help states structure the crash and roadway data needed for highway safety analyses in a standard format. The first is the Model Minimum Uniform Crash Criteria (MMUCC). MMUCC is a list of standard crash data elements and associated definitions developed by NHSTA. While the implementation of this model is voluntary, states are encouraged to adhere to the standard in collecting and compiling crash data. Similar in concept to the MMUCC, the Model Inventory of Roadway Elements MIRE is a list of over 200 roadway and traffic data elements critical to safety management developed by the FHWA.

Figure 2 - Categories and Subcategories for MIRE Data Elements:

I. Roadway Segment Descriptors

I.a. Segment Location/Linkage Elements
I.b. Segment Roadway Classification
I.c. Segment Cross Section

I.c.1. Surface Descriptors
I.c.2. Lane Descriptors
I.c.3. Shoulder Descriptors
I.c.4. Median Descriptors

I.d. Roadside Descriptors
I.e. Other Segment Descriptions
I.f. Segment Traffic Flow Data
I.g. Segment Traffic Operations/Control Data
I.h. Other Supplemental Segment Descriptors

II. Roadway Alignment Descriptors

II.a. Horizontal Curve Data
II.b. Vertical Grade Data

III. Roadway Junction Descriptors

III.a. At-Grade Intersections/Junctions

III.a.1. At-Grade Intersection/Junction General Descriptors
III.a.2. At-Grade Intersection/Junction Descriptors (Each Approach)

III.b. Interchange and Ramp Descriptors

III.b.1. General Interchange Descriptors
III.b.2. Interchange Ramp Descriptors

Credit: FHWA Website (Accessed 12/31/2016)

Collecting roadway data according to the MIRE model will not only benefit the state DOT in regards to traffic safety efforts, it will also help other core areas of transportation such as operations, asset management, and maintenance.


Once a section of roadway has been identified for needed safety improvements, an agency needs to decide which types of countermeasures would be the most effective. There are many types of safety countermeasures that could be implemented. Here’s a list of 9 proven countermeasures published by FHWA’s Office of Safety.

An interesting cost-benefit analysis of high-friction surface treatment was done by PennDOT in 2016. It found that the Benefit/Cost ratio was over 20:1. The report can be found here.

Assignment 7-1 (15 points)

Read FHWA’s August 2013 publication titled Assessment of the Geographic Information Systems’ (GIS) Needs and Obstacles in Traffic Safety. Submit an M.S. Word document to Assignment 7-1 in Canvas which addresses the following items:

  1. What did the 2012 Map-21 legislation and August 7, 2012 memorandum issued by FHWA’s Office of Highway Policy Information and Office of Planning, Environment, and Realty require states to do in regards to their base maps and LRSs? (2 points)
  2. According to the authors, what are some of the ways state DOTs use GIS as part of their highway safety programs? (3 points)
  3. List some of the techniques state DOTs are using to improve the collection crash data. (2 points)
  4. In their discussion of emerging technologies, the authors talk about the potential use of crowdsourcing to collect MIRE/roadway inventory data. How successful do you think that would be? (3 points)
  5. What are some of the challenges states face in collecting and integrating local data? (3 points)
  6. The authors discuss some opportunities for FHWA to improve states’ use of GIS in highway safety. If you had to pick one, which opportunity do you think makes the most sense and why? (2 points)

The Fatality Analysis Reporting System (FARS)

FARS is a system used to collect, store and analyze fatalities on U.S. roadways. The system is administered by the National Center for Statistics and Analysis (NCSA) which is part of the National Highway Traffic Safety Administration (NHTSA). The system includes data from all 50 states, the District of Columbia, and Puerto Rico. The primary purpose of the system is to monitor the effectiveness of vehicle safety standards and highway safety programs which are implemented at the state level. Only crashes which result in at least one fatality and occur on a roadway which is open to the public are included in FARS.

The Fatality Analysis Reporting System Encyclopedia. The type of fatality, the amount of fatalities, and and the year it took place from 1994-2014.
Figure 3 - NHTSA's Fatality Analysis Reporting System (FARS)
Credit: NHTSA Website (accessed on 1/1/2017)

Pennsylvania Crash Information Tool (PCIT)

Some states make crash data available to the public and other interested parties via a web portal. As an example, Pennsylvania makes crash information available via the Pennsylvania Crash Information Tool (PCIT).

Pennsylvania Crash Info Tool on the PCIT website
Figure 4 - Pennsylvania Crash Information Tool (PCIT)
Credit: PCIT Website (accessed on 1/1/2017)

Many of the reports on this site are similar to those in FARS. PennDOT is in the process of adding mapping capabilities to the next version of PCIT scheduled for release in the spring of 2017. Similar to FARS, PennDOT also makes raw crash data available. The PCIT site simply guides users to the PennDOT’s GIS Data Portal for this data.

Figure 5 - PennDOT's GIS Data Portal
Credit: PennDot's Data Portal Website (accessed on 1/1/2017)

Pennsylvania crash data is available from 1997 to 2015. Differences between the FARS crash data and PennDOT’s crash data include:

  • crash data from PennDOT include all reportable crashes and not just fatal crashes;
  • crash data from PennDOT includes many more attributes or “flags” which can be used to filter the crashes;
  • PennDOT’s GIS Data Portal provides very limited querying options (year and county only) and, consequently, the burden is on the user to filter the data to meet their needs.

Assignment 7-2 (20 points)

In this assignment, you’ll have an opportunity to work with crash data from FARS and PennDOT’s GIS Data Portal. Submit an M.S. Word document to Assignment 7-2 in Canvas which addresses the following items:

  1. Using the FARS system, create a thematic map (they refer to it as an intensity map) which shows how fatal crashes varied by state in 2015. Include a screen shot of the thematic map you produced in FARS. Which 3 states had the most fatal crashes? (5 points)
  2. Export crash data from FARS in Excel format which includes all 2015 fatal crashes in Centre County, Pennsylvania. Include the number of fatalities for each crash in the output. (Hint: Use query option 3 to get driver attributes. Also, don’t forget to include county so you can restrict the data to Centre County.) Import the crash data into ArcMap and create a map of the crashes where the symbology varies by the number of fatalities. The map should include county boundaries and one of the base maps ESRI makes available. Include a screen shot of your map. (5 points)
  3. Imagine you work for the Pennsylvania State Police and you are trying to identify good locations for DUI checkpoints in Centre County. To do so, you’re going to look at crash data for 2015 to see where alcohol-related crashes occurred. Since you want to consider all crashes which involved alcohol and not just fatal crashes, the FARS database will not be sufficient. Instead, use 2015 Centre County crash data available from PennDOT’s GIS Data Portal.
    1. Create a map which shows the crashes of interest. Include a screen shot of your map. This exercise will require you to convert the crash data to a feature class, join the crash feature class with the crash flags and use an attribute query to create the set of crashes you want. While there are a number of flags which you could use to identify these crashes, use the “alcohol_related” flag for this exercise. (5 points)
    2. Using the crash data, select 3 locations for DUI checkpoints. Create a screenshot of the map with the checkpoints designated on the map. You can either create a feature class for the checkpoints or simply place graphic symbols, available on the draw toolbar in ArcMap, where you want the checkpoints to be. Provide a brief rationale for your choices. (3 points)
    3. What additional information would be useful in helping you to establish good DUI checkpoints? (2 points)

GIS Uses and Benefits in Highway Safety

As we learned in Lesson 6, spatial technologies are used to locate crashes and perform crash analysis to locate crash hotspots, otherwise known as crash clusters. Spatial technologies also play a critical role in expanding network screening to include roadway characteristics and traffic data in addition to historic crash data as called for in the HSM. Spatial analyses not only help in identifying priority sections of roadway for safety improvements, but they can also be used to determine the countermeasures which are most likely to be effective and to assess their impact once they have been in place for a period of time. Finally, and perhaps most importantly, GIS plays a huge role in vehicle to vehicle communications and autonomous car technologies. These initiatives promise to have revolutionary impacts on highway safety and make the goal of 0 fatalities seem not so far-fetched.