Trees in Hazardous Locations: Appendix 17

Index of Strategies vs. Related Crash Factors

Exhibit 1 is an index of strategies for addressing crashes involving trees. The strategies listed are covered in the guide for the AASHTO Strategic Highway Safety Plan that addresses crashes involving trees in hazardous locations. In many cases, sites with tree crash problems may be amenable to correction using strategies designed to keep vehicles on the road. Strategies designed to mitigate ROR crashes may be found in the run-off-road accidents guide.

Crash reports will be the primary source of data for identifying and detailing problems, whether the analysis is being conducted for the entire road system, a large portion of it, or specific sites. Therefore, the table lists potential crash factors that may be present or over-represented in ROR crashes and related to them. The strategies that may be suggested for consideration by the over-representation of each factor are listed opposite them.

The crash factors in the table can be derived from a state or local police crash reporting form. Since state reporting forms are quite variable, a standard was used to identify the factors included in the table: the Model Minimum Uniform Crash Criteria (MMUCC).¹ Where that standard is not sufficiently comprehensive, the ANSI D20 standard for crash report elements is also referred to.²

Roadway inventory data may be available as an additional source to help relate problems to strategies. Where the scope of the analysis is limited to a relatively small portion of the road system, field studies can provide needed details to help select the appropriate strategies to consider. Other sources of data are sometimes available, which can help in the analysis. Details of the problem identification process are covered in the discussion of Step 1 of the Model Implementation Process.

All of the strategies listed in the guide for tree crashes could be applied to several of the crash factors. Even where this is not the case, more than one crash factor will be identified as significantly associated with the problem. 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 over-representation of both ROR crashes and vehicle striking trees planted on a non-recoverable slope, one should study the application of not only the strategies in the run-off-road accidents guide, but also Strategy 16.1 B3 (Modify Roadside Clear Zone in the Vicinity of Trees) in the guide for tree crashes, as well as such Strategies 16.1 B1 and 16.1 B2, which deal with removing the trees or shielding motorist from striking trees.

¹ Final Model Minimum Uniform Crash Criteria (MMUCC), established by NHTSA and FHWA in August 1998.

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