Safety and Driver Behavior Studies at Multiple Lane Approaches to Stop-Controlled Intersections

Multiple-lane approaches (MLAs) controlled by stop signs are becoming increasingly common in Nebraska. Installation of MLAs occurs when a single approach lane can no longer adequately serve the minor road traffic volume, and a signal is unwarranted because Manual of Uniform Traffic Control Devices (MUTCD) warrants are not satisfied (7, FHWA, 2003). A common example of a location at which MLA stop-controlled intersections can occur in Nebraska is the rural intersection of two state or federal highways. Forty such intersections in Nebraska were available for study in this research. Additionally, such intersections are often located in suburban areas of Nebraska municipalities where the local-collector network of a residential development connects to an arterial roadway. The objective of this research was to investigate driver safety and behavior at two-way stop-controlled MLA intersections. The reason for the investigation is to gain a better understanding of potential sight distance limitations due to side-by-side stopped vehicles at stop signs, as described earlier. Below is a summary of recommendations based upon safety study aspects of the project: Results of the before-after comparison group safety studies concerning crash frequency indicated that signalization of MLA-type intersections results in improved safety, however no statistically significant difference was found at the 95 percent confidence level. Results of the before-after comparison group safety study of the conversion of one MLA-type intersection to an SLA configuration showed that the crash frequency was reduced when the approach was changed to a single lane. However, the study of average crash rates indicated that the MLA-type intersection had a statistically significant lower average than the SLA intersection at the 95 percent level of confidence. Also, the reduction of the number of approach lanes from two to one can increase driver delay and user costs. Comparison of 3-year average crash rates at MLA intersections with 2-lane major roads with similar statewide intersection averages indicates that they have a higher than average rate when the roadway design necessitates a horizontal curve along the major road or minor road horizontal alignment in the near proximity of the point of intersection. Comparison of 3-year average crash rates at MLA intersections with 4-lane major roads with similar statewide intersection averages indicates that they have a higher than average rate when in urban areas. Therefore, use of this type of intersection along 4-lane urban roadways should be limited. If MLA-type intersections are determined to be the intersection type of choice: Provide consistent and redundant positive visual guidance to promote the positioning of right-turning drivers in advance of leftturning drivers at MLA-type intersections. Each visual cue issue, recommendation for improvement, explanation of recommendation and official guideline resource is summarized following FIGURES 38 and 39 in TABLE 24. FIGURE 40 shows a plan view of the proposed recommendations. Develop a combined text and iconic STOP AT LINE sign. Several designs should be tested with a pool of Nebraska drivers to determine the most easily interpreted design. Positioning of the sign should follow the guidelines in FIGURE 39 and TABLE 24. Provide better driver information about the new proposed sign and the appropriate stop position at a stop bar location in the Nebraska Driver’s Manual. Additional information should be provided on page 40 of the current Nebraska Driver’s Manual to better inform drivers about the desired stopping position at a painted stop bar on the pavement of a driving lane. Update an MLA-type intersection using the proposals defined in the research report and conduct a before-after field study. To better understand if the proposed recommendations result in a significant improvement in driver behavior, it is highly recommended that a field study be performed to quantify the improvement, if any