Unit 4

Contributing Crash Factors, Countermeasure Selection, and

Module 4.5Cost Effectiveness of Alternative Countermeasures

Module 4.5Cost Effectiveness of

Alternative Countermeasures

Learning Objective Duration 25 MinutesAt the conclusion of this module, participants will be able to:

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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Module 4.5Cost Effectiveness of Alternative Countermeasures 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, which 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

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 any ongoing cost required over the time period in question, such as maintenance NCHRP 17-40, June 2010

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Module 4.5Cost Effectiveness of Alternative Countermeasures 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.

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Module 4.5Cost Effectiveness of Alternative Countermeasures 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.

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.

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, NCHRP 17-40, June 2010

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Module 4.5Cost Effectiveness of Alternative Countermeasures 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.

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 NCHRP 17-40, June 2010

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Module 4.5Cost Effectiveness of Alternative Countermeasures 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.

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.

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 NCHRP 17-40, June 2010

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Module 4.5Cost Effectiveness of Alternative Countermeasures 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.

As discussed above, many considerations beyond safety typically enter into project selection. Some of these considerations may be quantified, but many are NCHRP 17-40, June 2010

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Module 4.5Cost Effectiveness of Alternative Countermeasures 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.

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.

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Module 4.5Cost Effectiveness of Alternative Countermeasures 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.

Let’s once again revisit our 4 intersections to see how we might use the SPF to evaluate the effectiveness of a countermeasure.

We decided sites A and C were our SWiPs. Let’s assume we have conducted our benefit-cost analysis and decided to treat site C.

For sake of convenience and visual clarity we’ll drop other data points and focus on the mean crash frequency at site C.

Let’s implement a countermeasure and see what the new average # of crashes is at the site.

Notice there was also an ADT change with the countermeasure

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Module 4.5Cost Effectiveness of Alternative Countermeasures

Let’s again drop the individual data and just show the meanSo, the question is: How do we evaluate the effectiveness of the countermeasure applied to site C?

One might assume the effectiveness is simply the difference between the frequency before the treatment and after.However, as discussed before, this does not account for regression-to-the-mean, variation, or the change in exposure. It also does not ask the right question:

What is the effectiveness of the countermeasure compared to what would have happened had the countermeasure not been implemented?

A more accurate basis for comparison goes back to the SPF and compares the crash frequency with the treatment to what we reasonably could expect if the countermeasure were not in place– all other things being equal except the countermeasure. Comparison of the expected crash frequency with the after crash frequency provides the more appropriate calculation since using the expected frequency accounts for regression to the mean, variance, and increased exposure. This turns out to be AMF W rather than AMF B. Which measure would show a greater change in crash frequency? (AMF B)

As indicated earlier this evaluation produces an AMF which, when aggregated with other AMFs across several locations, offers an estimate of the mean AMF for a treatment that can be used in future countermeasure selection and prioritization analyses.

Whenever possible, safety professionals should strive to use quantitative analysis to aid in the development of the road safety program. One of the most commonly used quantitative analysis methods is benefit-cost analysis. It involves the systematic comparison of all the countermeasure benefits NCHRP 17-40, June 2010

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Module 4.5Cost Effectiveness of Alternative Countermeasures (including reductions in injuries and fatalities and other benefits) to all of its costs (including the cost of implementing and maintaining the countermeasure over a given time period). Comparison of the benefits and costs yields a “benefit-cost ratio”. If the ratio is greater than one, the countermeasure is considered to add value.

The benefit-cost ratio alone is not sufficient to define the road safety program. The road safety professional must select among one of several mechanisms to translate the benefit-cost ratio or other indicators into a prioritized list of projects. These range from a simple list in which projects are ranked and implemented on the basis of their benefit-cost ratio, to sophisticated mathematical tools that allow selection of a package of projects that collectively optimize achievement of a set of objectives (safety, mobility, etc) while minimizing costs. Beyond the benefit-cost ratio, qualitative considerations also enter into the selection of the road safety program. Selection and political factors include design standards, tradeoffs, familiarity, and constituent concerns.

Post-countermeasure evaluation is a critical component of an viable safety program. Rather than using before-after analysis that does not account for regression-to-the-mean, variability, or changes in exposure, SPFs can be used to conduct more accurate with-without measures of effectiveness.

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