CHAPTER 5
Conclusions and Suggested Research

Conclusions

The safety effects of delineating roadside hardware and objects were evaluated through a crash data analysis and a human factors study. This project began with a review of previous research related to the delineation of linear roadside hardware and objects and the collection of delineation practices through a state survey. These practices were synthesized to identify common delineation types for roadside hardware and obstacles.

A crash data analysis focused on the safety effects of installing delineator panels on concrete barriers and post-mounted delineators on guardrails. Crashes were evaluated in select states that had installed these practices on their roadways. A simple before-and-after analysis approach was used to determine whether any safety benefit could be attributed to installing these delineation practices. In general, a reduction in crashes occurred at sites where delineator panels had been installed on concrete barriers and post-mounted delineators had been installed on guardrails. However, a couple of limitations were observed during the analysis. First, several states had small sample sizes (i.e., fewer than 20 crashes). Thus, it was difficult to substantiate the effectiveness of the delineation practices because the data were more susceptible to randomness. Of the eight states evaluated, only three had datasets with more than 20 crashes. Second, additional safety improvements were made at specific sites with the implemented delineation practice. For example, the roadway was repaved at some sites with post-mounted delineators installed on a guardrail system. Thus, an observed reduction in crashes could not be attributed solely to the influence of installing post-mounted delineators. While the safety trend does appear to be positive (i.e., a reduction in crashes) when these delineation practices are installed, additional investigation is recommended because of the limitations in the analysis. Specific suggestions for future investigation are discussed in the next section.

Also, a two-part human factors study evaluated driversʼ behavior and responses to different delineation practices for concrete barriers, guardrails, and culverts. The study comprised a closed-course and a computer-based study to evaluate the delineation practices, gathering data from vehicles driving through a representative roadway course and from a video and questionnaire-style survey. A total of 29 delineation practices were evaluated in the human factors study. Key findings from the study suggested an increased safety benefit when the roadside hardware devices and roadside obstacles were delineated. Additionally, specific delineation practices indicated a greater degree of effectiveness than others. For concrete barriers, the continuous retroreflective paint stripe and top-mounted delineator practices improved driver performance as drivers approached the curve. For guardrails, post-mounted delineators improved driver performance as drivers approached the curve. The evaluation of delineator panels installed on concrete barriers and guardrails was limited in the closed-course study; however, it had the highest driver-subjective preference among the delineation practices. For culverts, object markers improved

driver performance compared to delineator posts in detecting a roadside object. In addition, the driver-subjective preference was greater for object markers.

In summary, the delineation of roadside hardware and obstacles has shown improved safety benefits through reduced crashes and better driver behavior and responses. This effect was observed and evaluated for curved roadways and in dry daytime and nighttime conditions.

Suggested Research

Conducting additional research is suggested to continue evaluating the effects of delineating linear roadside hardware and obstacles. Additional topics and applications are summarized as follows:

1. The effects of delineation on other roadside hardware and obstacle types should be considered. This study evaluated concrete barrier, guardrail, and culvert delineation practices. A future study could focus on delineating other types of roadside hardware or consider other types of concrete barrier, guardrail, or culvert delineation practices not evaluated in this study.
2. The human factor study evaluated the delineation practices in a closed-course environment. A future human factors study could evaluate the delineation practices in a field environment. This approach would allow for improved, realistic roadway and environmental conditions.
3. The evaluation of the delineation practices was focused on curved roadways and dry daytime and nighttime conditions. Other driving conditions (e.g., wet, fog) should be considered when evaluating the effects of roadside hardware and roadside obstacle delineation practices.
4. One of the limitations of the crash data analysis was the lack of sites with delineation practices installed and the lack of information regarding the delineation installation (e.g., installation date, installation type). This limitation reduced the amount of available crash data to analyze and prevented the use of advanced crash analysis techniques. If more delineation practices are implemented and installed as a result of this research effort, a follow-up study could further analyze the safety effects of these practices.
5. Developing CMFs for delineation practices is encouraged. Similar to the previous suggested research topic, additional time may be needed for these devices to be implemented in the field.
6. Developing and evaluating delineation practices for work zones may help improve the safety of these conditions. The practices evaluated in this study were focused on standard roadway conditions. Modified and improved practices may be needed to appropriately delineate roadside hardware and obstacles for work zones.