6. EVALUATION RESULTS

This section of the report presents and interprets the results of the evaluations conducted using the YC, CG, and EB approaches. Detailed results of all evaluations conducted as part of the study are presented in appendix C. This section focuses on those evaluation results that were found to be statistically significant. All tests of statistical significance in this report were performed at the 5 percent significance level (95 percent confidence level) unless otherwise stated.

The evaluation results are tabulated in several different ways in this section. First, results tables for each dependent variable and target area are presented. Then, the same results are tabulated and reviewed by project type.

Evaluation Results for Specific Safety Measures

Tables 28 through 40 present the evaluation results for specific safety measures. The results for four-leg intersections are presented first. There are more statistically significant analysis results for four-leg intersections than for three-leg intersections because there were more treated sites and more accidents per site for four-leg intersections. The tables and the safety measures presented for four-leg intersections include:

• Table 28—total intersection accidents.
• Table 29—fatal and injury intersection accidents.
• Table 30—project-related intersection accidents.
• Table 31—project-related fatal and injury intersection accidents.
• Table 32—total accidents for individual intersection approaches.
• Table 33—fatal and injury accidents for individual intersection approaches.
• Table 34—project-related accidents for individual intersection approaches.

Each table shows all treatment effectiveness measures that were obtained for the YC, CG, and EB approaches. Only those results that were statistically significant are included. There is no table for project-related fatal and injury accidents on individual intersection approaches because none of the evaluation results for that safety measure were statistically significant for the YC approach and, because of low accident frequencies, appropriate regression models to conduct the CG and EB approaches could not be developed.

The tables and the safety measures presented for three-leg intersections include:

• Table 35—total intersection accidents.
• Table 36—fatal and injury intersection accidents.
• Table 37—project-related intersection accidents.

Note: Only statistically significant evaluation results are shown.

Note: Only statistically significant evaluation results are shown.

Note: Only statistically significant evaluation results are shown.

Note: Only statistically significant evaluation results are shown.

^a Because of small accident frequencies, regression models could not be developed for this safety measure. Therefore, the CG and EB evaluations could not be performed.

Note: Only statistically significant evaluation results are shown.

Note: Only statistically significant evaluation results are shown.

Note: Only statistically significant evaluation results are shown.

Note: Only statistically significant evaluation results are shown.

Note: Only statistically significant evaluation results are shown.

Note: Only statistically significant evaluation results are shown.

• Table 38—total accidents for individual intersection approaches.
• Table 39—fatal and injury accidents for individual intersection accidents.
• Table 40—project-related accidents for individual intersection approaches.

These tables are comparable to those presented above for four-leg intersections. There is no table for project-related fatal and injury accidents at three-leg intersections because no evaluation results for that accident type were statistically significant.

Evaluation Results for Specific Project Types

The evaluation results for specific project types are presented in tables 41 through 46. Specifically, the evaluation results by project type for four-leg intersections are presented in the following tables:

• Table 41—projects involving added left-turn lanes.
• Table 42—projects involving added right-turn lanes.
• Table 43—projects involving added left- and right-turn lanes.
• Table 44—projects involving extension of the length of existing turn lanes.

The evaluation results by project type for three-leg intersections are presented in:

• Table 45—projects involving added left-turn lanes.
• Table 46—projects involving added right-turn lanes.

There were no statistically significant evaluation results for projects involving addition of both left- and right-turn lanes or extension of the length of existing turn lanes at three-leg intersections, so no tables of evaluation results are presented for these project types.

The results in tables 41 through 46 are drawn from, and are identical to, the results in tables 28 through 40. However, results for the safety measures involving project-related fatal and injury accidents are omitted because only the YC approach could be evaluated for those cases and, even for the YC approach, very few statistically significant results were obtained due to low accident frequencies analyzed.

The next section addresses the choice among the alternative analysis methods presented in these tables. Then, the results for the specific project types can be interpreted.

Note: Only statistically significant evaluation results are shown.

Note: Only statistically significant evaluation results are shown.