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Wildlife-Vehicle Collision Reduction Study: Report To Congress

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Chapter 10. Evaluation of mitigation Methods by Technical Working Group

The WTI-Berger Team convened a Technical Working Group Meeting on January 25, 2007, at FHWA Headquarters. The Technical Working Group consisted of a panel of seven national experts in the area of WVCs. The experts were identified and selected by the FHWA Project Committee during the June 30, 2006, kickoff meeting. An effort was made to include representation from academia, State transportation departments, Federal agencies, and nongovernment organizations. The Technical Working Group members are listed in table 9.

*Participated by phone

The Technical Working Group reviewed a draft version of this report and helped identify other sources of information that would be beneficial. Another purpose of this meeting was to have a group of national experts evaluate the effectiveness of the mitigations based on their knowledge. Initially, the Project Committee (FHWA) and the WTI-Berger Team wanted to use the NCHRP 500 categories for safety mitigations. The categories defined in the NCHRP 500 report are:

Tried (T)—Those strategies that have been implemented in a number of locations and may even be accepted as standards or standard approaches but for which valid evaluations have not been found. These strategies, while in frequent or even general use, should be applied with caution, carefully considering the attributes cited in the guide and relating them to the specific conditions for which they are being considered. Implementation can proceed with some degree of assurance that there is not likely to be a negative impact on safety and very likely to be a positive one. As the experiences of implementation of these strategies continues under the AASHTO Strategic Highway Safety Plan initiative, appropriate evaluations will be conducted, so that effective information can be accumulated to provide better estimating power for the user, and the strategy can be upgraded to a "proven" one.⁽³⁹⁷⁾

Experimental (E)—Those strategies that have been suggested and that at least one agency has considered sufficiently promising to try on a small scale in at least one location. These strategies should be considered only after the others have proven not to be appropriate or feasible. Even where considered, their implementation should initially occur using a very controlled and limited pilot study that includes a properly designed evaluation component. Only after careful testing and evaluations show the strategy to be effective should broader implementation be considered. As the experiences of such pilot tests are accumulated from various state and local agencies, the aggregate experience can be used to further detail the attributes of this type of strategy so that it can be upgraded to a "proven" one.⁽³⁹⁷⁾

Proven (P)—Those strategies that have been used in one or more locations and for which properly designed evaluations have been conducted that show it to be effective. These strategies may be employed with a good degree of confidence, but with the understanding that any application can lead to results that vary significantly from those found in previous evaluations. The attributes of the strategies that are provided will help the user judge which strategy is the most appropriate for the particular situation.⁽³⁹⁷⁾

A properly designed evaluation for the "proven" category has a fairly strict definition in the safety field, including a Bayesian analysis of crash data. (Note: Bayesian analysis evaluates the consistency or inconsistency of new evidence with a given hypothesis.) Bayesian analysis does require the a priori assignment of probabilities to hypotheses, which, depending on the question, may be subjective. As an example, a mitigation that has been proven to keep animals off the road would not be proven if no studies on WVCs with a Bayesian analysis were completed, even though logically these would be known to be effective. The Technical Working Group concluded that under this definition, none of the mitigations would be defined as proven, and almost all of the mitigation measures would be classified in the "tried" category. The Working Group members felt that the strict safety definitions would not do justice to their experience with certain mitigation measures and effectiveness data gathered on them. The meaning of "properly designed evaluation" was left up to the individual members of the Technical Working Group and did not require a Bayesian analysis of crash data. To avoid confusion with the safety definitions, the names of the above three definitions were changed. Also, two categories were added. The new definitions adopted by the Technical Working Group for this evaluation were:

• Successful (similar to "proven" safety definition): Mitigation measures that have been used in one or more locations and for which properly designed evaluations have been conducted that show them to be effective.

• Demonstrated (similar to "tried" safety definition): Mitigation measures that have been implemented in multiple locations and that may even be accepted as standards or standard approaches but for which valid evaluations have not been found.

• Attempted (similar to "experimental" safety definition): Mitigation measures that have been suggested and that at least one agency has considered sufficiently promising to try on a small scale in at least one location. However, data on effectiveness have not been documented or have not yet been published.

• Unknown: Mitigation measures that have not been tried or that have been tried, but not for WVC reduction, were not implemented correctly, or are only recently being tried.

• Failed: Mitigation measures that have been used in one or more locations and for which properly designed evaluations have been conducted and show them NOT to be effective.

The procedure for voting was as follows. The mitigation was described by the WTI-Berger Team. The panel members were asked to base their vote on the effectiveness in reducing DVCs. The vote was not based on mitigation for other effects related to roads and traffic (e.g., barrier effect) or for species other than deer (white-tailed and mule deer combined). Deer are involved with the majority of all reported WVCs (chapter 2). If panel members had been asked to consider multiple species representing very different species groups, the procedure would have had to have been repeated for each species or species group. Limited data are available to evaluate the effectiveness of many of the mitigation measures for species other than deer.

After hearing a description of each individual mitigation measure, the Technical Working Group voted. If the vote was unanimous, the next mitigation was considered. If there was contention, the panel discussed the rationale for their votes, and the members were allowed to change their votes based on new information provided by the other panel members. However, a unanimous vote or consensus was not required.

The results of this process are shown in table 10. The mitigation "reduce speed by posting advisory speed signs" was not included since the Group felt this was very similar to warning signs. The mitigation "carcass removal" was also not included since the Group felt that this mitigated for scavengers only and not for deer. The mitigation "increase visibility of animals to drivers: reduce height of snow banks" was not included because this section was added to the report after the ranking meeting. Most of the mitigations that provide crossing opportunities are not included, since their purpose is to mitigate the barrier effect of fencing and are not mitigations for WVCs by themselves.

*Although this mitigation has not been proven through evaluation procedures, it is intuitive that it definitely works.

**Although this technique has been tried, it was not implemented appropriately.

Note: ROW = right of way.

Although the above table gives good insight into what works and what does not, most of the mitigations fall into the uncertain categories (demonstrated, attempted, or unknown). Also, it does not take into account costs of implementation, feasibility of implementation, and overall effectiveness. As a follow-up, the Technical Working Group was asked (by email) to categorize the same mitigation measures as the following:

• Recommended for implementation.
• Recommended for further research.
• Not recommended for implementation or further research.

The results of this categorization are presented in table 11. Note that, relative to this second categorization effort, there are some mitigations where one or more members of the group did not vote.

Note: ROW = right of way.

Referring to table 11, the panel voted on whether each mitigation measure should or should not be implemented or whether further research should be undertaken. A majority of votes (four or more) was required to make a positive recommendation for implementation of the mitigation measure. Also, a majority of votes (four or more) for "not recommended" resulted in the rejection of the mitigation measure. Finally, if a majority did not cast votes to recommend implementation, but at least four votes were divided between "recommended" and " further research," the panel's recommendation was that further research should be undertaken for that particular mitigation measure.

When interpreting the results, it is important to keep in mind that these opinions only relate to deer and to mitigating DVCs. The opinions do not necessarily relate to other species or mitigating other effects associated with roads and traffic such as habitat loss, reduced habitat quality, and barrier effect (except for direct road mortality). The subsequent outcome of this process is as follows:

• Where feasible and appropriate, the following mitigations should be implemented:

• Public information and education.

• Wildlife fencing.

• Underpasses and overpasses with fencing.

• Research or construction resources should not be used for the following mitigations:

• Standard wildlife warning signs.

• Deer reflectors and mirrors.

• Audio signals in the right of way or deer whistles on vehicles.

• Olfactory repellents.

• Deer flagging models.

• Hazing.

• Intercept feeding.

• Wildlife relocation in order to reduce population size.

• Anti-fertility treatment in order to reduce population size.

• Seasonal road closures.

• Reflective collars placed on wildlife.

• Mitigations that may be promising, but require further investigation include the following:

• Reduce traffic volume on road network.

• Reduce speed by reducing the posted speed limit.

• Reduce speed by traffic calming or reducing the design speed.

• Wildlife crossing guards.

• Large, nonstandard wildlife warning signs.

• Seasonal wildlife warning signs.

• Animal detection systems.

• In-vehicle warnings: roadside animal detection system communicating with on-board computers.

• In-vehicle warnings: on-board animal detectors.

• Increase visibility through roadway lighting.

• Increase visibility through vegetation removal.

• Investigate deicing alternatives.

• Influence plant species in the roadside to limit nutritional value.

• Reduce population size through wildlife culling.

• Reduce population size through habitat alteration.

• Boulders forming a barrier.

• Long tunnels and long bridges.

• Overpasses and underpasses by themselves.

• Wider more reflective striping along white line.

• Expanded median.

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