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 provided about 2.2 billion dollars to the states for safety projects.
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.
State DOTs commonly 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 the 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. My presentation was just under 10 minutes in length (embedded video below).
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.
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.
Countermeasures
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 20 proven countermeasures published by FHWA’s Office of Safety.