1. Road Safety Management Process
After discussing data issues in Unit 3 last week, we are now going to talk about factors that contribute to crashes; methods for selecting effective countermeasures; strategies for prioritizing countermeasures; and the necessity of doing an evaluation.
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2. Roadway Safety Management Process4 5 6 7 8 9
Prioritization of Improvement Projects
Network Screening
Countermeasure Selection
Network Screening 4 5 6 7 8 9
Here is the slide that we saw earlier. Based on the Highway Safety Manual, the process is a 6 step process. In this module we are going to mainly talk about network screening.
Part B covers the roadway safety management process. Offering tools across the following tasks:
Network screening
Diagnosis of sites with potential for improvement
Countermeasure selection
Economic appraisal
Prioritization of improvement projects
Safety effectiveness evaluation.
Diagnosis
Economic Appraisal
Safety Effectiveness Evaluation

3. Methods for Identifying Sites
The identification, examination and effective treatment of well-chosen sites will yield safety improvements…
The identification and examination of well chosen sites will yield safety improvements.
Key Words: “Well-chosen” sites
“Effective” Treatments
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4. Methods for Identifying Sites
Goal – Identify and rank “sites with promise”
Those sites that, if treated, will experience decreases in crashes
Example methods
Public involvement? Political pressure?
High crash frequency history
High crash rate
Severity-weighted frequency (based on crash costs)
Excess crashes
Etc.
This module discusses statistical models for identifying “sites with promise” or those sites that will be improved if treated. Indeed, since we are trying to maximize the “bang for the buck,” the best sites would be those that show the most effect for the least dollars spend. Define those sites (before we treat) is very difficult.
So how should we choose sites for potential treatment?
Public involvement? Political pressure?
High crash frequency history
High crash rate
Severity-weighted frequency (based on crash costs)
Excess crashes
Etc.
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5. Example: Excess Crashes
Compare actual crashes to expected crashes for this category of sites (e.g., two-lane rural intersections)
We will discuss methods for identifying the expected number of crashes more in Unit 4. For our purposes at this point, it is important to just know that good methods exist for selecting sites with promise or those sites where significant safety improvements can be predicted. For example, the prediction model shown on the slide is for calculating the expected number of intersection crashes on two-lane rural roads. The elements considered in the equation include: average annual daily traffic on a major road (vehicles); average annual daily traffic on a minor road (vehicles); median width of major road in feet; and number of driveways within 250 feet of the intersection center point.
If for example, the predicted number of crashes is .38 or about one every three years, and the site experiences 0 or 1 crash in a particular year, you wouldn’t worry very much about it. On the other hand, if the site experienced 8 crashes in a single year, it might indicate that the site should be scrutinized more closely.
It is through the routine comparison of expected safety performance and observed safety performance that sites are identified for further scrutiny. While statistical models are often used to identify potential sites, other methods also are used such as political pressure, public involvement, etc.
More details in Unit 4
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6. Network Screening
Identify sites that may benefit the most from a treatment
Establish Focus
Specific crash types (e.g., wet weather crashes)
Specific facility types (e.g., intersections)
Specific area/corridor
Select reference population
Groups of sites with similar characteristics
Select performance measures
Select screening method and do the screening
The intent of network screening is to identify sites that may benefit the most from a treatment.
Here are the steps involved in network screening.
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7. Performance Measures
13 performance measures listed in the Highway Safety Manual
Range from very simple measures based on average crash frequency to advanced measures based on the empirical Bayes method
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8. How to Select a Performance Measure?
Data Availability
Is traffic volume data available?
Are Safety Performance Functions available? If no, can they be estimated?
Does the performance measure account for Regression-to-the- Mean Bias
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9. How to Identify Sites with Promise?
Expected Number of Crashes
Excess Expected Difference compared to the average for comparable sites (also called deviation from the norm)
Can be used Identify deviant sites
Can use empirical Bayes method to estimate expected crashes
Once you select a performance, how can you use that information to identify sites with promise. Here are a couple of examples. One is to select sites based on the expected number of crashes. Second is to use something called excess expected difference compared to the average value for comparable sites – this can be used to identify deviant sites
You could use the empirical Bayes method to estimate the expected crashes. We will see a hypothetical example in the next slide

10. Determining deviant sites
Expected crashes (based on EB method)
Excess A
Crashes per Unit Time
SPF representing average for comparable sites (norm)
The vertical axis shows the crashes per unit time and the horizontal axis shows traffic volume. The Curve is the SPF which represents average crash frequency for comparable sites (which is also called the norm)
The point A is the expected crashes for site A (based on the EB method)
Excess expected is this gap between A and the average for this traffic volume. Excess is also called deviation from the norm.
Traffic Volume

11. Diagnosis Crash Factors Collision Type Human Roadway Vehicle
Environmental
Collision Type
Run-off Road
Rear End
Head On
Sideswipe Same Direction
Once you identify the sites based on the screening process, you need to examine these sites more carefully to find out why they have a problem and what are the contributing factors – whether they are human, roadway, vehicle, or environmental. This process can repeated for different crash types.
To do this you can field studies or audits and also closely individual police crash reports.
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12. Site Review Methods Engineering Road Safety Audits Crash history
Immediate improvements (maintenance)
Low cost safety improvements
High cost safety improvements
Crash history
Collision diagram
When high crash locations and road segments are identified through data analysis, safety engineers typically conduct an engineering study to determine what can be done from an infrastructure perspective. Increasingly these reviews are supplemented by a road safety audit to bring a more multidisciplinary and multimodal perspective.
As discussed previously, Road Safety Audits, traditionally at least were aimed at systematic review of new highway designs and changes in design during the design process; well before any construction was undertaken and continuing throughout the completion of the project. Road Safety Audit Reviews, on the other hand, focus on existing locations. [CORRECTION: FHWA defines RSAs as the process that can be conducted at every stage in the lifecycle of a transportation facility including pre-construction, construction, and post-construction as discussed in the FHWA Road Safety Audit Guidelines, FHWA-SA-06-06]
The output of an RSAR is likely to be a set of alternative actions to improve safety at the site in question. The recommended actions are likely to be divided into 3 categories:
Immediate safety improvements – countermeasures that can be implemented immediately (e.g. clearing vegetation and sight obstructions)
Low cost improvements – relatively low cost actions that can improve safety such as signing
High cost improvements
The multidisciplinary aspects of the review are largely a function of the composition of the review team and the commitment of the organizing entity to establish a multidisciplinary team. This may be a weakness inherent to the process because the road owner may not be committed to the process.
Most of the examples provided in the reviewed literature emphasize engineering, specifically design features. Perhaps this is a legacy of the RSA origins; however, addressing pedestrian risks, particularly for older pedestrians, is one aspect mentioned in RSARs that could easily reflect human factors and other disciplinary interests.
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13. Example Collision Diagram

14. Motives for Action Economic Efficiency
Professional and Institutional Responsibility
Fairness
Once the diagnosis is completed, there may be different motivations on which sites should be targeted for action:
Motive 1: Economic efficiency -- identify sites at which a treatment would be cost-effective. To do this, you need to know the how effective a treatment will be and what we will be the cost of installing and maintaining the treatment.
Motive 2: Professional and institutional responsibility -- Identify and correct sites that are deficient because of how they were built or because they have deteriorated (i.e., eroded shoulder lanes).
Motive 3: Fairness -- Identify sites that pose an unacceptably high risk to a specific set of users (i.e., older drivers). These are often low exposure sites that would not otherwise appear on a “list” based on crash frequency.
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15. Countermeasure Selection
In this module we will discuss and examine helpful tools and methods for selecting effective countermeasures and targeting specific audiences.
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16. Tools For Identifying Countermeasures
Engineering studies
Road safety audits
The Australian Safe Systems Approach
The Haddon matrix
So that’s one method for identifying potential sites for treatment. How do we then choose the right countermeasure for a given site or corridor? What are potential tools for identifying countermeasures?
Engineering studies
Road safety audits
The Australian Safe Systems Approach
The Haddon matrix
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17. Engineering Studies Step 1: Examine the Crash Data
Step 2: Conduct a Field Study
Step 3: Identify Potential Countermeasures
Step 4: Prioritize Countermeasures
Step 5: Implement the Chosen Countermeasure(s)
Step 6: Evaluate the countermeasure impact
Highway safety professionals seek to identify the most effective countermeasures for improving road safety. One method is through a typical engineering study which involves several steps:
Examine the crash data.
Conduct a field study.
Identify countermeasures.
Prioritize the countermeasures by establishing which will bring the most benefit for the fewest resources.
Implement the countermeasures.
Evaluate the effectiveness of the countermeasures.
Engineering studies may be supplemented by road safety audits (RSA).
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18. Road Safety Audits
Used for Roadway Corridors, Both Existing and New (Canada)
Characteristics of RSAs
A formal examination with a structured process;
Conducted independently by professionals who are not currently involved with the project;
Completed by a team of qualified professionals representing appropriate disciplines;
Focuses solely on safety issues; and
Examines the transportation site with respect to all potential road users.
Engineering studies are often used when we are analyzing specific sites. They may be supplemented by road safety audits (RSA) when we are analyzing corridors. They can be used after a road is in use (to determine possible modifications, or even before a newly-constructed road is open to traffic (as is done in parts of Canada)
The road safety audit (RSA) is typically a proactive tool for improving safety. When combined with modeling information, the Haddon matrix, engineering studies, etc., RSAs serve as an important activity for continually assessing and improving safety within a jurisdiction. RSAs typically have the following characteristics: (NCHRP, 2004):
1. A formal examination with a structured process and not a cursory review;
2. Conducted independently by professionals who are not currently involved with the project;
3. Completed by a team of qualified professionals representing multiple disciplines;
4. Focuses solely on safety issues; and
5. The RSA examines the transportation site with respect to all potential road users.
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19. The Australian “Safe Systems Approach”
Can’t Prevent All Crashes
But Try To Assure No Serious Injuries or Deaths
How?
Safer vehicles
Safety roads and roadsides
Controlling speeds
Australians have developed the “safe systems” approach. The implication is that while we may not be able to prevent all crashes, we should be able to assure that, given involvement, no one is injured or killed. This is accomplished by controlling speeds, designing safer vehicles, and constructing safer roads and roadsides. The idea is to turn our thinking on its head. Instead of saying, “Why did that bloody idiot hit that utility pole?” We should be thinking, “Why did that bloody idiot put that utility pole there to be hit.”
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20. The Haddon Matrix Crash-Related Factor Categories Crash Time Human
Vehicle
Roadway
Environmental
Crash Time
Pre Crash
Crash
Post Crash
The Haddon Matrix is commonly used to approach safety analysis at a site in a systematic fashion. The Haddon Matrix was developed in 1980 by William Haddon (Haddon, 1980), and contains nine or more elements for possible focus for road safety.
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21. The Haddon Matrix (cont.)
Can be use to
Categorize existing treatments to identify cells with few
Categorize factors (e.g., fatigue, ambulance delay) to generate new treatments.
Element
Pre Crash
Crash
Post Crash
Human
Vehicle/
Equipment
Road/Physical Environment
The Haddon matrix can be used in a number of ways with two of the most prevalent being:
Categorize existing treatments to identify cells with few
Categorize factors (e.g., fatigue, ambulance delay) to generate new treatments.
The nine cells of the matrix represent time phases of the crash in addition to human, vehicle, and road factors related to the event. It is common to add a fourth row element that represents environmental conditions such as weather, etc., socio/economic conditions, etc.
The Haddon matrix is completed through the evaluation of sites and/or crash details associated with a site or sites. When completed, it provides insight into the range of possible safety issues and concerns as well as possible solutions.
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22. The Haddon Matrix -- Exercise
Graduated Drivers Licensing
Airbags
Driver risk-taking propensity
Seat Belt Use
Distance to hospital
Electronic stability control
Driver age
Emergency Med. Svs. Training
GPS automatic crash notification
Rumble strips
Median barrier
Distance to roadside object
Element
Pre Crash
Crash
Post Crash
Human
Vehicle/
Equipment
Road/Physical Environment
This exercise is to use the Haddon matrix in countermeasure generation. Recall that we noted that the cells can be filled with both existing treatments, or existing factors needing (better) treatments. Please write down the list on the left and beside each one, chose the cell that it fits in (e.g., Pre-crash, human).
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23. The Haddon Matrix (cont.)
Element
Pre Crash
Crash
Post Crash
Human
GDL
Risk Taking
Driver Age
Seat Belt Use
Vehicle/
Equipment
Electronic Stability
Airbags
GPS Auto-Notification
Road/Physical Environment
Rumble Strips
Distance to Object
Median Barrier
Distance to Hospital
EMS Training
The nine cells of the matrix represent time phases of the crash in addition to human, vehicle, and road factors related to the event. It is common to add a fourth row element that represents environmental conditions such as weather, etc., socio/economic conditions, etc.
The Haddon matrix is completed through the evaluation of sites and/or crash details associated with a site or sites. When completed, it provides insight into the range of possible safety issues and concerns as well as possible solutions.
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24. Sources for Potential Countermeasures
Roadway Countermeasures
NCHRP Series 500
Highway Safety Manual, Part D
FHWA Crash Modification Factor Clearinghouse
FHWA list of suggested (proven) countermeasures
NCHRP Report 617, Accident Modification Factors for Traffic Engineering and ITS Improvements
Behavioral Countermeasures
Countermeasures That Work
These are some of the potential sources of countermeasure for use. Most are roadway related, but the bottom one is an excellent guide (updated regularly) which concerns behavioral countermeasures. We will now discuss some of these in a little more detail.
DANIEL, I didn’t include a slide spacer for the 617 report. Here is your information from later if you want to say it now:
NCHRP Report 617 documents several AMFs from previous studies to determine which could be used with a high or medium-high level of certainty. The study also developed AMFs for 35 high priority treatments or treatment combinations widely used by states and local agencies. The process documented in this study could be used in future efforts to develop or improve AMFs. .
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25. Countermeasure Sources: NCHRP Series 500 Guides
Countermeasures classified as:
Proven,
Tried, or
Experimental
Examples:
Relocate roadside objects (P)
Install shoulder rumble strips (T)
Delineate poles with retroreflective tape (E)
The NCHRP 500 series guidebooks were developed to support implementation of the AASHTO Strategic Highway Safety Plan. (safety.transportation.org/guides.aspx). The idea was to provide tools and encourage all the states to develop SHSPs. Subsequently, of course, SAFETEA-LU included a requirement for all states to develop and implement a SHSP and as of October 1, 2007, all states and the District of Columbia had approved SHSPs.
The guidebooks are organized around the concept of safety problems (e.g., aggressive driving, run-off-road crashes, etc.). A process for addressing the problem is described in each of the reports and includes issues in plan development such as building a constituency, identifying champions and other steps in the planning process. These are discussed in more detail in the final module of this course.
For each problem several countermeasure are proposed and discussed. These have been developed from a review of the available literature and the experience of the project team. Each countermeasure is classified in one of three categories: proven; tried or experimental.
Proven countermeasures have shown a demonstrated effect on the problem being addressed.
Tried countermeasures have been attempted, but for which definitive evidence of effectiveness is not available or uncertain.
Experimental treatments have been suggested and/or implemented but have received little if any field evaluation.
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26. Countermeasure Sources: Highway Safety Manual
First edition released in 2010
Provides practitioners with the best factual information and tools regarding safety consequences of design decisions.
Sections
Part A: Safety knowledge
Part B: Safety management
Part C: Crash prediction models
Part D: Countermeasure selection and CMFs

27. Countermeasure Sources: Crash Modification Factors Clearinghouse

28. Countermeasure Sources: FHWA Suggested Countermeasures (2008)
Road safety audits
Rumble strips and rumble stripes
Median barriers
Safety edge
Roundabouts
Left and right turn lanes at stop-controlled intersections
Yellow and all red change intervals at traffic signals
Median and pedestrian refuge areas in urban and suburban areas
Walkways
In 2008 FHWA fine tuned the “hit list” and published Consideration and Implementation of Proven Safety Countermeasures ( This 2008 FHWA memorandum identifies when and where certain processes, techniques, and countermeasures should be used. It provides detailed information on nine proven effective countermeasures for addressing safety issues including:
Road safety audits;
Rumble strips and rumble stripes;
Median barriers;
Safety edge;
Roundabouts;
Left and right turn lanes at stop-controlled intersections;
Yellow and all red change intervals at traffic signals;
Median and pedestrian refuge areas in urban and suburban areas; and
Walkways.
Ask: What is the difference between a roundabout and a traffic circle?
Answer: A roundabout is one of several types of circular road junctions or intersections at which traffic is slowed down and enters a one-way stream around a central island. Technically these junctions sometimes are called modern roundabouts, to emphasize the distinction from older circular junction types which had different design characteristics and rules of operation. In the United States those older designs commonly are referred to as "rotaries" or "traffic circles". Modern roundabouts are particularly common in Australia, the United Kingdom, Ireland, and France. Half of the world's roundabouts are in France (over 30,000 as of 2008).[2] The first modern roundabout in the United States was constructed in Summerlin, Nevada in 1990[3], and roundabouts have since become increasingly common in North America.
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29. Countermeasure Sources: NHTSA “Countermeasures That Work”
NHTSA’s Countermeasures That Work: A Highway Safety Countermeasure Guide For State Highway Safety Offices (3rd Edition, 2008) is a basic reference to assist in selecting effective, science-based traffic safety countermeasures relevant to road user crash factors. The guide summarizes major strategies and countermeasures, their effectiveness, costs, and implementation time, and provides references to research summaries and individual studies.
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30. Question
When faced with many potential countermeasures, how does one choose which one(s) to implement?

31. Comparing Countermeasures
Subjective comparisons
Which will garner the most public support?
Which is most appropriate for the area?
Objective comparisons
Expected effectiveness -> decreases in crashes (CMFs)
Expected costs -> installation and maintenance

32. Market Research for Targeting Countermeasures
Identifying sub-population characteristics
Easing language barriers
Customizing campaigns and programs
Market research techniques can be used to target countermeasures to particular high risk groups. These strategies have the potential to foster a stronger relationship between transportation safety planning and high risk groups and reduce the crash risks of these groups.
Ask: What are the potential impacts of targeting high risk groups?
Answer:
Identify sub-population characteristics – Using market research techniques to target sub-populations may help safety planners, highway safety practitioners, transportation officials, engineers, et al, understand unique cultural, socioeconomic, or behavioral characteristics to consider when developing countermeasures and programs. Many safety program campaigns are designed to target a general population and do not take advantage of the opportunity to target high risk sub-groups.
Ease language barriers – Specialized market research techniques can offer safety programs the opportunity to communicate with sub-populations in the language that they are most comfortable reading and speaking. It may be necessary to use the techniques to identify the language most commonly spoken or the variation of the language most often used by the group.
Customizing campaigns and programs - Educational materials to discourage teen driving under the influence of alcohol should have a different message than one designed to target the general adult population. The teen program would highlight the dangers of driving under the influence and the laws that prohibit alcohol consumption by individuals under the legal drinking age. The teen campaign might also talk about peer pressure and how to say no to drugs and alcohol. Such messages are not as appropriate for adults.
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33. Market Research Techniques
What types of market research techniques can be used to target high crash risk groups?
Ask: What types of market research techniques can be used to target high crash risk groups?
Answer:
Focus Groups - A facilitator or group leader uses scripted questions or topics to lead a discussion among a group of people. These sessions should be held in a neutral location because the location can influence the participation of sub-population groups. Focus groups can be used to gather a sub-population’s opinion of public information and education materials and ads; discuss transportation safety issues relative to the sub-population; and to hear their opinions of countermeasures used to address the problems.
Surveys – Mail or phone surveys can be used to collect information related to sub-population groups. Surveys help identify characteristics of high crash risk sub groups, risk factors, opinions on safety issues, and exposure to media.
For example, the Florida DOT conducted a public opinion telephone survey to gather information related to motorcycle rider characteristics, risk factors, public opinion of safety, and recollection of media campaigns. The survey asked questions that gauged internet use and television channel and radio station preferences. Behavioral practices such as helmet use and speeding were also integrated into the survey.
Observational Studies – Responses to surveys and focus groups are sometimes not indicative of people’s actual behavior. Observational studies allow groups to be observed for certain behavioral characteristics and habits. This techniques is typically used to conduct safety belt use observation studies.
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34. Market Research Techniques
Focus groups
Surveys
Observational studies
Ask: What types of market research techniques can be used to target high crash risk groups?
Answer:
Focus Groups - A facilitator or group leader uses scripted questions or topics to lead a discussion among a group of people. These sessions should be held in a neutral location because the location can influence the participation of sub-population groups. Focus groups can be used to gather a sub-population’s opinion of public information and education materials and ads; discuss transportation safety issues relative to the sub-population; and to hear their opinions of countermeasures used to address the problems.
Surveys – Mail or phone surveys can be used to collect information related to sub-population groups. Surveys help identify characteristics of high crash risk sub groups, risk factors, opinions on safety issues, and exposure to media.
For example, the Florida DOT conducted a public opinion telephone survey to gather information related to motorcycle rider characteristics, risk factors, public opinion of safety, and recollection of media campaigns. The survey asked questions that gauged internet use and television channel and radio station preferences. Behavioral practices such as helmet use and speeding were also integrated into the survey.
Observational Studies – Responses to surveys and focus groups are sometimes not indicative of people’s actual behavior. Observational studies allow groups to be observed for certain behavioral characteristics and habits. This techniques is typically used to conduct safety belt use observation studies.
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35. Cost Effectiveness of Alternative Countermeasures
Prioritize interventions and countermeasures based on effectiveness.
Once you have identified the SWiPs, contributing crash factors, and a list of candidate countermeasures, you will need to prioritize the list. This module suggests methods for prioritizing a list of proposed countermeasures or interventions.
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36. Major Topics Countermeasure Costs and Benefits Programming Projects
Qualitative Considerations
Countermeasure Evaluation
Solutions to a safety problem may be low or high cost; may take an educational, engineering, or enforcement approach; may involve a ‘quick fix’ or a long term strategy. Safety professionals are constantly challenged to weigh the menu of possible solutions and to prioritize those that best address the problem at hand given existing constraints. The prioritized list of projects together forms the road safety program.
Whenever possible, safety professionals should strive to use quantitative analysis to aid in the development of the road safety program. This analysis typically consists of identification and comparison of the cost both installation and maintenance), effectiveness, and resilience (how long it is effective) of each countermeasure or program, using the latest information available from the research literature.
Quantitative information lends objectivity to a decision-making process that might otherwise be dominated by political considerations or subjective judgment. It helps ensure that the maximum safety benefit will be obtained for the amount of funds invested.
This module discusses quantitative concepts, such as cost, effectiveness, and resilience, that can be used in prioritizing a list of safety projects or programs. It also presents considerations beyond project costs and benefits that often enter into prioritization decisions.
Major topics include:
Quantitative concepts
Countermeasure benefits and costs
Programming projects
Qualitative considerations
Countermeasure evaluation
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37. Countermeasure Costs Startup or installation costs
Example?
Ongoing operational or maintenance costs
Resilience/staying power (“usable life”)
Which countermeasures would have shorter staying power? Which would be longer?
Some safety interventions cost much more than others. Geometric improvements to the roadway, such as straightening a tight curve to reduce run-off-road crashes, tend to be very expensive. Installing a “curve warning” sign addresses the same problem, but at a much lower cost. Safety professionals take these relative costs into consideration when prioritizing among countermeasures.
Part of calculating the cost of a countermeasure is considering how those costs might vary over time. This includes considering not only the original installation cost, but also any ongoing cost required over the time period in question, such as maintenance costs, as well as the relative resilience or “lasting power” of the countermeasure. One countermeasure may be just as effective as another in the short term, but less cost-effective over a longer time horizon. For example, installing speed cameras along a corridor requires significant up-front cost, but over time may be less than the cost of paying for enforcement each year along the corridor.
Formal benefit-cost analysis takes resilience into account by calculating all of the project benefits and costs over a given time horizon. That way, different countermeasures can be compared even though the timing of their impact varies. The engineering community has some catching up to do in measuring resilience. Good metrics are generally unavailable.
Particularly important given limited resources, quantitative concepts help safety professionals develop a road safety program that maximizes “bang for the buck”. One method of determining “bang for the buck” is to calculate the “benefit-cost ratio” for each countermeasure and to use those ratios to select and prioritize countermeasures for implementation. The benefit-cost ratio is the ratio of all of the benefits associated with the countermeasure (e.g. crash reduction, etc), expressed in monetary terms, to the cost of implementing the countermeasure. At a minimum, the benefit-cost ratio for a project should be greater than one for the project to be accepted. The resulting ratio can then be used to rank competing countermeasures. Understanding what the benefit-cost ratio means requires considering costs and benefits in more detail.
Sometimes a safety countermeasure will produce benefits beyond safety benefits, e.g. mobility improvements, reduced congestion, etc. With safer, less congested roadways, indirect benefits can also occur, such as improved environmental quality and economic prosperity.
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38. Countermeasures Benefits
Crashes prevented – use CMFs to estimate if available
Changes in crash severity
Signals and red light cameras
Cable median barriers
Other benefits not related to safety (e.g., reduced delay)
As mentioned above, the calculation of a benefit-cost ratio requires all project benefits to be expressed in monetary terms. This requires predicting both (1) the number of crashes that will be avoided as a result of implementing the countermeasure and (2) the cost in monetary terms of each crash avoided.
Estimating crashes avoided is often difficult, since it requires knowing the effectiveness of each countermeasure being considered. Countermeasure effectiveness is established through research studies undertaken by academic institutions or other organizations. These studies aim to determine the percent reduction in crashes resulting from a given countermeasure, which we’ve learned is referred to as the “accident modification factor” (AMF), or the “crash reduction factor” (CRF).
Unfortunately, as we’ve also learned, reliable AMFs or CRFs are not always available for a countermeasure, especially for non-engineering countermeasures such as educational or enforcement strategies or for experimental engineering treatments. In these cases, safety professionals must use a greater degree of subjective judgment when selecting countermeasures. They may also consider whether any proven treatments exist that could meet the established goal, or whether experimental / untried treatments can be used alongside proven ones.
Another complication when considering the limitations of benefit-cost analysis is the fact that fewer crashes is not necessarily a positive outcome. If a countermeasure reduces the number of crashes but increases crash severity, the overall result may be a reduction in safety. For instance, cable median barriers are a well-accepted strategy for reducing the incidence of head-on collisions in run-off-road crashes. They do not necessarily reduce the number of run-off-road crashes, but do improve safety by reducing crash severity. This example illustrates the fact that it is always important to consider both the likely change in number of crashes and the likely change in crash severity when calculating the benefits of a safety countermeasure.
Safety countermeasures have many direct safety benefits, including reductions in injuries, fatalities, and damage to personal property. They may also provide direct benefits not related to safety. For example, signal synchronization can improve both safety and mobility by reducing queuing.
A full accounting of all the benefits associated with a countermeasure would also include many indirect benefits, since crashes cause substantial indirect harm to individuals and society. One recent report identified 11 types of costs associated with crashes, including property damage; lost earnings; lost household production; medical costs; emergency services; travel delay; vocational rehabilitation; workplace costs; administrative; legal; pain, and lost quality of life. These costs amount to several hundred billion dollars a year in the United States alone.
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39. Countermeasure Benefits: Crash Modification Factors
Crash modification factor (CMF) is a multiplicative factor used to compute the expected number of crashes after implementing a given countermeasure at a specific site.
CMF =
CMF > 1 indicates an expected increase in crashes
CMF < 1 indicates an expected decrease in crashes
Expected crashes with countermeasure
Expected crashes without countermeasure
One tool for assessing countermeasure benefits in terms of crash reduction is an accident modification factor or AMF. AMFs are defined as: the expected number of crashes with a countermeasure divided by the expected number of crashes without a countermeasure.
This comparison with and without is traditionally conducted at one location and then aggregated across several locations to obtain an estimate of the mean AMF for a treatment.
Note that the ratio involves expected values not counts, so the discussions in prior modules concerning estimation of mean crash frequency apply here. The expected number of crashes without should be obtained by using the Bayes estimate of the expected number of crashes at the site without the countermeasure in place (often this is the SPF value for a specific facility type and ADT).
It is also likely that the AMF has been defined in terms of this ratio for specific crash types. For example, when considering AMFs for changes in shoulder width, it seems logical to consider run-off-road events or crash events that evolve from changes in lane-keeping such as head-on and side-swipe.
As part of the development of the broad theme of the science of safety, strong concerted effort is taking place to develop quantified AMFs based upon actual field data. This should be recognized as a departure from the position of assuming a facility is safe if certain safety guidelines or standards are met. The quantification of the safety implications of our actions are translated to hard numbers through the AMF.
Accident modification factors pivot around the number 1.0 which conveys no change in expected number of crashes. AMFs greater than 1.0 imply an increase in the number of crashes; AMFs less than 1.0 imply a reduction. Both numbers are from a given baseline.
So, in addition to the AMF, any discussion of their use must include the baseline value from which the adjustments are to be made. For example, for lane width, the baseline is 12 feet; for shoulder width either 6 feet or 8 feet have been used. It is essential in any AMF use that the baseline value be clearly identified and correctly applied to the action to be taken.
NCHRP 17-40, June 2010

40. Countermeasure Benefits: Issues in developing CMFs
Isolating specific treatments or populations
Data availability
Detailed data not collected (e.g., installation date, etc)
Countermeasure not installed anywhere yet
Time
Money
Cost and time have been major problems in developing AMFs from the rigorous definitional approach of implementing a single countermeasure and then estimating a AMF as the ratio of the expected number of crashes divided by the expected number without. Among the difficulties are:
Countermeasures are often implemented in combination with other actions, and it is difficult to separate the effect of the countermeasure from the effect of additional actions;
It may be difficult to wait long enough to accumulate a sufficient crash record to conduct with–without comparison;
This type of evaluation tends to be much more costly than naïve before and after evaluation; and
Often the expertise is not available on staff.
In response to these concerns researchers have tried a variety of approaches to expand our knowledge base of quantified AMFs.
NCHRP 17-40, June 2010

41. Countermeasure Benefits: Tools and Resources for CMFs
Highway Safety Manual
CMF Clearinghouse
SafetyAnalyst
The Interactive Highway Safety Design Model (IHSDM)
NCHRP Report 622, Effectiveness of Behavioral Highway Safety Countermeasures
Having listed the potential issues associated with AMFs, it is important to point out that when valid they provide a key component of existing safety tools and resources used by state and local agencies in prioritizing safety programs. Some tools and resources that agencies can utilize for credible AMFs include:
The Highway Safety Manual (HSM) ( which is currently under development, provides safety practitioners with information on the effects of various safety treatments in chapters on roadway segments, intersections, interchanges, special facilities and geometric situations, and roadway networks. A screening process was used to evaluate AMFs for the manual which included a review by a panel of experts to determine if the results were sufficiently reliable.
AMFs are being incorporated into the economic appraisal tool in FHWA’s SafetyAnalyst ( which is currently being tested by several states.
The Interactive Highway Safety Design Model (IHSDM) is a product of the FHWA’s Safety Research and Development Program, utilizes AMFs to predict the expected safety outcomes of various roadway or rehabilitation designs (
With the current absence of reliable behavioral AMFs, NCHRP Report 622: Effectiveness of Behavioral Highway Safety Countermeasures builds on NHTSA’s Countermeasures that Work by providing more specific metrics for estimating the costs and benefits of emerging, experimental, untried, or unproven behavioral countermeasures. (
NCHRP 17-40, June 2010

42. Countermeasure Benefits: Assigning Monetary Value to Crashes Prevented
Complex Process
Rules of Thumb
Fatal plus Serious Injury vs. minor injury plus PDO Costs
Cost Effectiveness
Once the number of crashes avoided is known, it is transformed into a monetary value by multiplying by the cost of each crash. The process of assigning monetary values to avoided crashes is complicated and will not be discussed here.
For simplicity, most transportation organizations have developed “rules of thumb” to use when assigning costs to avoided crashes. Typically, costs are tiered based on the expected crash severity, but they can also be differentiated by the type of vehicle involved (motor carrier versus passenger vehicle); the roadway location (rural versus urban) or by the roadway functional class since all these factors could potentially influence the cost of the crash. In reality, we probably need two AMFs when calculating cost-benefit: one for serious injury and fatal crashes and one for property damage only crashes.
In situations where it is not possible or practical to monetize countermeasure benefits, a “cost-effectiveness” metric can be used in lieu of the cost benefit ratio. Cost effectiveness is simply the amount of benefit (not expressed in monetary terms) per dollar invested. It is often expressed as the number of crashes avoided for every dollar invested in a certain countermeasure.
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43. Countermeasure Benefits: Example Crash Costs
Killed – K
$4,008,900
Disabling Injury – A
$216,000
Evident Injury – B
$79,000
Possible Injury – C
$44,900
Property Damage Only – O
$7,400
This table shows an example of the costs of crashes prepared by the FHWA. As one would expect, fatal crashes “cost” much more than less severe crashes, so the benefit associated with avoiding fatal crashes is much greater. Note: in 2008 FHWA recalculated the cost of fatalities and increased the amount to over $5M. However, the agency has not yet published equivalent metrics for other severity levels.
In 1994, Ezra Hauer published an article titled: Can one estimate the value of life or is it better to be dead than stuck in traffic? In an analysis of whether to replace STOP signs by YIELD signs, the value of a life lost was pegged at $1,500,000 and the value of time at $6.71/hour. These numbers imply that when the sum of traffic delays accumulated by many drivers is equal in duration to the average lifetime lost in a fatal crash (37.3 years), the cost of such delay is higher than the cost of an average lost life.
Source:  Highway Safety Manual, First Edition, Draft 3.1, April 2009.
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44. Benefit and Cost Analysis
Striving for the most effective use of limited safety funds (“bang for the buck”)
Rank competing projects
Methods
Benefit-cost ratio
Present value of benefits

45. Example Benefit-Cost Ratios
Countermeasure benefits
Benefit-cost ratio =
Countermeasure costs
This graphic shows an example of typical benefit-cost ratios from the Minnesota Department of Transportation Traffic Safety Fundamentals Handbook. We must be cautious and make sure we take the context into account when using benefit-cost ratios. Difference contexts, such as road type, average daily travel, rural/urban, etc. will produce varying cost-benefit ratios.
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46. Project Programming Techniques
Ranking
Weighting
Linear Programming
Calculating benefit-cost ratio or a cost-effectiveness metric helps identify whether a project or set of projects are worthwhile. As stated previously, if the benefit-cost ratio exceeds one, the project may be considered to add value. Benefit-cost ratios alone, however, do not tell the safety professional how to rank and implement a set of projects within a given budget. The safety professional must select among several different techniques to do this. One simple technique is to rank the projects based on their benefit-cost ratio and to go down the list of projects until the budget is depleted. Another technique is to invest all available funds in the types of projects with the highest benefit-cost ratio.
The ranking process becomes more complicated when other factors beyond safety are taken into consideration. In fact, as will be discussed in the next section, it is common for safety to be just one among many priorities that public organizations must balance, such as mobility, environmental concerns, economic development needs, and so on.
Several tools are available to assist in selecting projects while taking into account multiple objectives. One is to incorporate those objectives into the benefit-cost analysis itself by estimating and monetizing any non-safety benefits such as congestion mitigation, air pollution reduction, and other benefits. The resulting benefit-cost ratio will reflect all of the additional benefits included. Projects can then be implemented in order based on their benefit cost ratio.
A simpler, but less scientific method is to score each project for how well it meets the objectives (e.g., safety improvement, mobility improvement, etc), and then multiply the score in each category by a weight that corresponds to the importance of the objective. Projects can then be implemented in order based on their composite score.
An alternative to simply implementing projects in order based on a single metric (score, benefit-cost ratio, etc) is to select a package of projects that together provide the maximal benefit at minimal cost. A mathematical technique known as linear integer programming can be used for this purpose.
Software programs are under development that will assist in the selection and ranking of countermeasures. Whatever technique is selected, safety professionals must work to ensure safety has a place within the prioritization scheme. Without a safety champion, the organization may not consider safety at all when selecting projects. Or the organization may consider safety, but assign it a low priority compared to other objectives.
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47. Other (Qualitative) Considerations
What are other considerations that can play a role in which countermeasures are implemented?
As discussed above, many considerations beyond safety typically enter into project selection. Some of these considerations may be quantified, but many are subjective and political. Nevertheless, they still play an important role in the project selection process. Some of these considerations include:
Design standards. Some safety countermeasures, especially untested or innovative countermeasures, may conflict with established design standards. Violating design standards may be politically risky, and may bring exposure to lawsuits if a crash occurs in the area where the standard was violated. For these reasons, decision-makers may avoid innovative or untested countermeasures that potentially violate design standards.
Trade-offs. As discussed above, transportation organizations have many concerns beyond improving safety, such as improving mobility or reducing the environmental impact of transportation systems. Countermeasures perceived to conflict with other priorities may meet with resistance. For example, installation of a protected left-turn signal arrow may be opposed because it increases the amount of time drivers have to wait at the intersection.
Familiarity. Some individuals or organizations may oppose implementation of certain countermeasures simply due to lack of familiarity. Decision-makers and stakeholders often come to the table with different perspectives on how to solve a problem or may have a vested interest in a specific solution. For example, engineers might oppose educational or enforcement solutions to a safety problem because they are unfamiliar with the potential benefits.
Constituent concerns. Elected officials may be in favor of or oppose certain countermeasures due to the concerns of their constituents. If the constituents demand a particular solution to a safety problem, the politician may support it regardless of cost-effectiveness.
These are important concerns, but the question is how to integrate these into science-based safety decisions – how do we combine these with data-driven inputs? We probably don't yet have a great answer yet, If two or three potential countermeasures have similar BC ratios, then clearly these other considerations such as constituent concerns would be a great “tie-breaker.” However, until we get a better means of incorporating these, science-based safety requires that we use data-based findings as the primary input to decisions.
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48. Other (Qualitative) Considerations
Design Standards
Tradeoffs
Familiarity
Constituent Concerns
How do we integrate these into science-based safety decisions?
As discussed above, many considerations beyond safety typically enter into project selection. Some of these considerations may be quantified, but many are subjective and political. Nevertheless, they still play an important role in the project selection process. Some of these considerations include:
Design standards. Some safety countermeasures, especially untested or innovative countermeasures, may conflict with established design standards. Violating design standards may be politically risky, and may bring exposure to lawsuits if a crash occurs in the area where the standard was violated. For these reasons, decision-makers may avoid innovative or untested countermeasures that potentially violate design standards.
Trade-offs. As discussed above, transportation organizations have many concerns beyond improving safety, such as improving mobility or reducing the environmental impact of transportation systems. Countermeasures perceived to conflict with other priorities may meet with resistance. For example, installation of a protected left-turn signal arrow may be opposed because it increases the amount of time drivers have to wait at the intersection.
Familiarity. Some individuals or organizations may oppose implementation of certain countermeasures simply due to lack of familiarity. Decision-makers and stakeholders often come to the table with different perspectives on how to solve a problem or may have a vested interest in a specific solution. For example, engineers might oppose educational or enforcement solutions to a safety problem because they are unfamiliar with the potential benefits.
Constituent concerns. Elected officials may be in favor of or oppose certain countermeasures due to the concerns of their constituents. If the constituents demand a particular solution to a safety problem, the politician may support it regardless of cost-effectiveness.
These are important concerns, but the question is how to integrate these into science-based safety decisions – how do we combine these with data-driven inputs? We probably don't yet have a great answer yet, If two or three potential countermeasures have similar BC ratios, then clearly these other considerations such as constituent concerns would be a great “tie-breaker.” However, until we get a better means of incorporating these, science-based safety requires that we use data-based findings as the primary input to decisions.
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49. Post-Implementation Evaluation
Evaluation is essential to establish countermeasure effectiveness
Funds should be set aside for scientific evaluation
Once road safety professionals have achieved political support for a list of countermeasures, they need to plan for post-implementation evaluation. This is a very important step because it is the best mechanism for determining the effectiveness of the countermeasure. Without it, there is no information on the actual benefit of the countermeasure and no data to justify its future use.
Unfortunately, post-implementation evaluations are often neglected because all funds are consumed in implementing the countermeasure itself. Safety professionals must make the case early on that funds should be set aside for evaluation. If they wait until the countermeasure has been implemented, in all likelihood, no remaining funds are available for the evaluation.
Enough funds should be set aside to allow a proper, scientific evaluation of the countermeasures whenever possible. If funds are not sufficient, the sponsoring agency may resort to a simple comparison of the number of crashes that occurred before and after the countermeasure was applied.
This type of comparison may lead to erroneous conclusions regarding the effectiveness of the countermeasure. A proper evaluation must take into account other variables that could have an effect on the number and/or severity of crashes, such as any change in the number of vehicles using the corridor (e.g., exposure), changes in demographics (proportion of older or younger drivers in the area), and so on.
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50. Example Collision Diagram – After Countermeasure Was Installed
Crashes decreased. Was all of the decrease due to the conversion to all way stop?

51. Countermeasure Evaluation: A Limited Primer
Methods for developing CMFs (i.e., evaluating countermeasures)
Study of sites/groups where a treatment is implemented (a “before-after” evaluation where a change has occurred)
Comparison of some sites/subjects with treatment vs. other similar sites/groups without treatment (e.g., median widths)
No real change has occurred
Usually involves developing a predictive model with lots of factors
There are difficulties with developing true measure of the treatment effect
We will just look at first type – evaluations where something really changed (i.e., a treatment was implemented)
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52. Countermeasure Evaluation: Goal and False Causes
Goal – Measure true effect of a countermeasure
We want to be sure that the observed change is due to the countermeasure alone
What other factors could cause the change?

53. Countermeasure Evaluation: Goal and False Causes
Goal – Measure true effect of a countermeasure
We want to be sure that the observed change is due to the countermeasure alone
What other factors could cause the change?
Other “treatments” at the same time (e.g., primary seat-belt law at the same time as adding a protected left-turn phase to intersections)
Changes in AADT
Regression to the mean
Underlying trends in crashes (e.g., economy-related changes)
Others
So how do we control for/discount these other “causes”?

54. Countermeasure Evaluation: Controlling for Other Causes
“Before vs. After” is misleading
Should be, “Estimated After (without treatment) vs. Observed After (with treatment).
How well we estimate the after (without treatment) crashes defines the strength of the evaluation
Different ways to estimate the after (without treatment) crashes
Use only the observed after treatment crashes (assume nothing changes – weakest)
Use of similar comparison groups to estimate (can use SPF prediction based on comparison group)
Use of Empirical Bayes to estimate (weighted between predicted and observed)
Randomly assign large group of similar sites to treatment or control group (like a drug study) and estimate based on non-treated control group

55. Evaluation – Summary That’s all!
Lots of hard work in planning, collecting data, statistical analysis and interpretation of results
BUT, when you are reading evaluation reports, just remember:
The strength of the study results depends on how well After-Crashes Without Treatment were estimated!