Head-On Collisions: Appendix 13

Choosing the Roadway-Related Strategy

The earlier sections have provided details of proven, tried, and experimental strategies aimed at reducing crashes, injuries, and deaths resulting from Head-On crashes. After a "location" (i.e., system, corridor, section, spot) has been identified for potential Head-On (HO) crash treatment, the question arises as to which of the strategies, or combinations of strategies, is most appropriate. The choice of strategy to be implemented will depend upon many factors-the existing character of the roadway and roadside at the site, available roadway width, strategies already in place, available funding, neighborhood considerations, and jurisdiction treatment and maintenance policies, among others. Thus, the choice of appropriate strategy or strategies cannot be provided by a "formula," but must be based on safety considerations, engineering analysis, and knowledge.

The usual approach to selecting a strategy, when working in a responsive mode, is to begin by considering the nature of the crash history. For example, if there is an overrepresentation of skidding crashes on wet pavement, one might immediately consider the need to provide skid-resistant pavement surfaces as a candidate.

However, identifying candidate strategies to study is not always so straightforward. For example, one might find that examination of the "Most Harmful Event" or "Sequence of Events" indicates an overrepresentation of HO crashes at a site. This knowledge might point one to a strategy such as "install buffer median". However, even though this strategy would likely be very effective, one may also be able to prevent the vehicle from leaving its lane in the first place. In fact, jurisdictional treatment-policy may direct that the first priority be given to keeping vehicles in their lane. Thus, a range of crash characteristics must be used. Furthermore, all potentially appropriate strategies should be considered, whether they directly or indirectly deal with the problem. The result will often be a list of candidate strategies, which should be studied for possible use, either singly or in combination. The best method for determining the appropriate combination of strategies to apply is some form of cost-effectiveness or cost-benefit analysis.

This process involves the examination of the crash data for the "location" being analyzed, searching for crash factors that might be frequently present or over-represented in HO crashes, and choosing strategies which are related to these specific crash factors. Exhibit 1 lists various crash data elements, and links them to candidate strategies for addressing a HO crash problem. Strategies for both basic objectives are included in the table.

Since the content of state reporting forms is currently quite variable, a standard has been used to identify the factors included in the table. That standard is the Model Minimum Uniform Crash Criteria (MMUCC)¹. Where that standard is not sufficiently comprehensive, reference is also made to the ANSI D20 standard for crash report elements².

This examination of crash characteristics will often result in the identification of more than one strategy that might be appropriate for a given "location." In these cases, the sum of strategies associated with each of the factors, as listed in Exhibit 1, should be considered. For example, if the analysis suggests that there is an overrepresentation of sites with skidding on wet pavement and vehicles overtaking/passing maneuvers associated with HO crashes, then strategy 15.1 A7, dealing with pavement skid resistance, should be included in the list of candidate strategies along with such strategies as 18.1 A3 and 18.1 B1 (which are associated with providing passing lanes).

The linkage between crash factors and candidate strategies that is provided in the table is the simplistic approach to the task of identifying appropriate strategies to use. It is not feasible to provide anything with greater depth or detail. The process that the analyst must go through will be different for each case, due to the complexity of the considerations and factors involved. Therefore, in making the final choice of which of the potential strategies to implement, the analyst would further examine all potential strategies in terms of the factors noted earlier-the existing character of the roadway at the site, available roadway width, strategies already in place, available funding, agency policies and practices, stakeholder requirements, etc.

Finally, it should be remembered that the table contains only roadway-oriented strategies. As discussed above, there are potentially applicable strategies related to enforcement, public information and education, emergency medical services, and system management, which may also be considered to improve the HO crash situation. For more on this, please refer back to the section entitled "Related Strategies for Creating a Truly Comprehensive Approach."

¹ Final Model Minimum Uniform Crash Criteria (MMUCC), established by NHTSA and FHWA in August of 1998 (http://www.nhtsa.dot.gov/people/perform/trafrecords/pages/mmucc/mmucc_documents.htm)

² ANSI D20 is a comprehensive data dictionary for crash reports, available from the American Association of Motor Vehicle Administrators (AAMVA)