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Focusing on Crash Severity in HSIP Project Selection

Publication Year: 2015


Virginia and Maryland

Description

Crash data remains a fundamental component of virtually any safety analysis. States use it to identify spot safety improvements, screen for systemic safety improvements, diagnose specific safety concerns, select countermeasures, and justify HSIP investments. But which crash data should States use? And how should they consider the severity of a crash when making safety decisions?

Since the passage of Moving Ahead for Progress in the 21st Century Act (MAP-21), States have placed greater focus on measuring safety performance, particularly in reducing the number and rate of traffic fatalities and serious injuries. This increases the focus on crashes most severely impacting society and human life while reducing the significance given to crashes resulting only in property damage or minor injury. States have worked to accommodate these changes in their Strategic Highway Safety Plans (SHSP) and are also finding ways to place greater emphasis on fatal and serious injury crashes throughout their HSIP processes.

States most commonly use the “KABCO” severity scale, developed by the National Safety Council to measure the observed injury severity for any person at the scene of a crash, to classify the severity of roadway injuries. The Fourth Edition of the Model Minimum Uniform Crash Criteria codes crashes as Fatal Injury (K), Suspected Serious Injury (A), Suspected Minor Injury (B), Possible Injury (C), and No Apparent Injury (O). Many States have interpreted “fatal and serious injuries” as including just “KA” or “KAB” injuries, and the most aggressive States only use data for these crashes in all aspects of their safety analysis.

As an example, the Virginia Department of Transportation (VDOT) gives highest improvement considerations to locations that have experienced “K” and “A” injuries. They develop statewide listings and maps of high crash routes and intersections following the SHSP Emphasis Areas. VDOT's central office provides these to district staff to identify candidate locations for project development, including intersections ranked by Deaths (type “K”) plus Severe Injuries (type “A”) in the most recent three years within each jurisdiction. Those locations in the top 5% are first priority. Those between the top 5% and 15% are second priority, and the remainders are lower priority.

map of the Annandale, Virginia area from VDOT TREDS Mapping 2014

Figure 1. Sample VDOT Freeway High Crash Location Map (Source: VDOT TREDS Mapping 2014)

Other States primarily use fatal and serious injury crash data, but also apply broader ranges of crash data and different screening criteria for certain crash types. For example, the Illinois DOT uses “all crashes” in their identification of high-risk horizontal curves, one of their SHSP priority emphasis areas. However, they use “all crashes” as part of the Highway Safety Manual (HSM) methodologies to identify curves where the observed crash frequency exceeds the expected frequency (calculated using the State's safety performance functions [SPFs]), or where there exists an excess proportion of specific crash types.

A third approach used by many states utilizes a weighted severity index or Equivalent Property Damage Only (EPDO) methodology, in which crashes are given different, pre-determined values depending on their severity. For example, a property damage only (PDO) crash may only have a value of one, but an incapacitating injury crash may have a value of 10. This would effectively give a crash with a category “A-injury” ten times the weight of a crash with no injury. In the Maryland DOT, this kind of weighting system is used to identify Critical Safety Improvement Locations (CSILs) and prioritize them for review and improvement. Figure 2 provides the weights Maryland uses when calculating their CSIL list. Although the system does not dismiss less severe crashes, it gives much higher weight to intersections and segments that have more serious injury crashes.

Severity Weighting Factors
Fatality 15
Incapacitating Injury 7
Non-incapacitating Injury 4
Possible Injury 2
Property Damage Only 1

Figure 2. Maryland Crash Weighting Factors (Source: Maryland SHA)

Finally, States also place greater weight on fatal and serious injury crashes in their analysis by either using dollar amounts to document the costs and benefits or limiting their analysis to only fatal and serious injury crashes. In addition, some states focus on countermeasures that have a particular effectiveness in preventing some of the most serious crashes (e.g., cable medial barrier to prevent cross-over head-on collisions).

Key Accomplishments

  • Safety issues posing the greatest risk of fatal and serious injury crashes receive higher priority
  • States place greater emphasis on investments to reduce the most serious crashes

Results

States are shifting away from simply focusing on reducing crashes and toward identifying the best opportunities and countermeasures for reducing crashes resulting in fatalities and serious injuries. This contributes to HSIP funding decisions that move states closer to achieving the national goal in MAP-21 “to achieve a significant reduction in traffic fatalities and serious injuries on all public roads.”

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Contacts

Tracy L. Turpin
Highway Safety Improvement Programs Manager
1401 E. Broad St., Room 207
Richmond, VA 23219
(804) 786-6610
Tracy.Turpin@VDOT.Virginia.gov

William (Bill) Macleod
Maryland State Highway Administration
707 North Calvert Street
Baltimore, Maryland 21202-3601
WMacleod@sha.state.md.us

Publication Year: 2015

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