Develop Highway Safety Performance Function Calibration Factors for Alaska
Summary
Title: Develop Highway Safety Performance Function Calibration Factors for Alaska
Proposing Agency: University of Alaska Anchorage
Proposal Date: December 2014
Principal Investigator (PI): Prof. Osama Abaza, Ph. D., Professor of Civil Engineering
Project Funds: $150,000.00
Project timeframe: Starting January 1, 2014, and expected to be completed by December 30, 2016
Full Report: https://goo.gl/kXXNHQ
Introduction
The Highway Safety Manual (HSM) is used to give safety appropriate consideration in the development of transportation projects, and was developed to help measure the reduction of frequency and severity of crashes on American roadways. The HSM acts as a predictive tool for designers, engineers, and planners in selecting countermeasures and prioritizing projects, comparing alternatives, and quantifying and predicting the safety performance of roadway elements (i.e. lane width, shoulder width, curve radius, control devices, signal phasing . . . etc.) considered in planning, design, construction, maintenance, and operation. The HSM was originally published in 2010 and now incorporates a most recent 2014 supplement.
The American Association of State Highway and Transportation Officials Highway Safety Manual provides a system to quantitatively analyze the safety of existing roadways and identify which geometric characteristics of current sites are correlated with high crash rates. To raise awareness about the frequency, severity, and locations of crashes and provide a tool to mitigate the occurrence of crashes, the Highway Safety Manual was calibrated specifically for Alaska.
The ability to measure and predict roadway safety is an important component of local agencies’ and community efforts to maintain and enhance their road systems safety. Historically, there have been a number of tools developed to help owners/agencies monitor and evaluate the safety of their roadway systems. 
The HSM was developed to quantitatively evaluate the different features of roadways. The methods advocated by the HSM have proven useful across the United States. However, some areas of the United States have features and characteristics that are notably different from the locations where the models were originally developed. A comparison of the predicted accident rate versus the actual accident rate at locations dissimilar to these areas would be useful for effectively utilizing HSM methods in those areas.
Alaska is different from many other states within the United States in many ways. Some are related to Alaska's northern climate. However, not all of Alaska's unusual features can be attributed to its latitude. Like every geographic area in the United States, Alaska has developed its own unique culture that is influenced by its climate, wildlife, location, history, and the people who live here.
Nature of the problem
Alaska's current Highway Safety Improvement Program (HSIP) practice uses previous crash experience to identify locations for safety projects. However, previous crash experience does not necessarily predict future crash events. Moving Ahead for Progress in the 21th Century (MAP- 21) says states should identify projects to improve safety, not only on the basis of crash history, but also on crash potential. Federal Highway Administration (FHWA) encourages states to adopt "a more comprehensive and proactive approach to prevent the most severe crashes by using risk analysis techniques within a data driven process to identify sites for potential safety improvement. FHWA calls this process Systemic Safety Project Selection. While Alaska has begun mining data sources to help identify system elements for possible improvements, there are tools available, such as the HSM, to help analyze all the risk factors and evaluate various countermeasures to maximize safety performance. The American Association of State Highway Transportation Officials (AASHTO) published the first edition of the HSM in 2010. The stated purpose of the HSM is to provide "safety knowledge and tools in a useful form to facilitate improved decision making based on safety performance. The importance of the HSM lies in its ability to assign quantitative crash values to road segments, intersections and entire road systems based on the physical attributes of the roadways in question. The HSM methods are tools which may benefit Alaska's HSIP, but state-specific calibration factors are needed for the best results. Application of the HSM depends on calibrating generic Safety Performance Functions (SPFs) to crash experience on Alaska's facilities. This requires application of HSM calibration techniques, availability of crash and volume data, and information on geometric features.
Research Objectives
The following two objectives will be addressed in this study:
1) Calibration of HSM predictive models using Alaska data for two-lane rural highways, four-way signalized intersections and stop control intersections.
2) Develop guidelines for future calibration of HSM predictive methods for other facilities not covered in this project or which may be addressed by the future edition of the HSM.
Expected Outcomes
The project will use the HSM Part C to develop local calibration factors for Alaska for two lane rural highways, four way signalized and stop control intersections. Local calibration factors for each facility per region will be developed if applicable.