Pavement Marking Demonstration Projects: State of Alaska and State of Tennessee
CHAPTER 7. RESEARCH SUMMARY AND FINDINGS
This chapter provides a summary of findings regarding a pavement marking demonstration project carried out in Alaska and Tennessee. The findings of the four major elements of the project are provided in the following sections.
COST EFFECTIVENESS OF PAVEMENT MARKINGS
Findings on cost effectiveness of pavement markings are as follows:
- Three pavement marking test decks (one in Alaska and two in Tennessee) were installed to evaluate the durability of various pavement marking materials, including advanced acrylic pavement markings. The results of the test decks, combined with pavement marking material and installation costs, were used to study the cost effectiveness of the pavement marking materials studied.
- Using key pavement marking degradation factors, a framework for a PMST was developed. The PMST was populated with data from the test decks in Tennessee to demonstrate the usefulness of such a tool.
- The test deck in Alaska proved to be a harsh environment for pavement markings of any type. Most of the markings tested on this test deck were deemed inadequate after the first winter, even when installed in a recessed groove to minimize plow damage. Paint-based pavement marking systems, including the advanced acrylic pavement markings, were unable to maintain retroreflectivity and presence past the first winter season. The only markings that maintained adequate presence through the first two winters were extruded MMA and tape. The tape product did not provide the same level of presence on the lane line as compared to the edge line. It is believed that the added weaving to which lane lines are exposed is responsible for the accelerated degradation of the tape product. The markings that maintained adequate retroreflectivity the longest were the structured MMA (not the splatter pattern but a longitudinal raised dual rib pattern) and the tape on the edge line.
- One strategy that AKDOT uses effectively is to apply a durable MMA marking in a groove and then remark the MMA with low-VOC paint each spring to provide adequate retroreflectivity through the summer and fall. This procedure provides a marking with year-round presence and retroreflectivity from the time the markings are restriped with paint in the spring until the paint wears away during the winter. Without considering the indirect costs of traffic delays and risk of crashes involved with more frequent striping activities, this may be the most cost effective method for the conditions tested on the Alaska test deck. One option that may be equally effective and reduce potential environmental concerns is the use of low-temperature advanced acrylic paint in place of the low-VOC paint for the spring painting activities.
EFFECTS OF WIDER EDGE LINE PAVEMENT MARKINGS
Operational effects include the following:
-
Earlier operational effect studies conducted on wider pavement markings have been inconclusive, showing inconsistent and/or insignificant findings.
- The crash surrogate study results are not different from previous research findings. After converting edge lines from 4 to 6 inches, small differences were detected in the mean and variance of vehicle speeds and lateral position (and of speed change from the beginning to the midpoint of curves). However, these changes were subtle and based on previous research and are not practically significant.
Safety effects include the following:
-
Earlier crash studies conducted with wider pavement markings have shown no particular benefit, partly because of a lack of adequate data.
- This study provided a unique opportunity to obtain the data needed to conduct a methodical examination of the safety benefits of wider edge lines. Two different approaches were used. One was based on crash frequency, and another was based on crash severity. The results are as follows:
- Crash frequency analyses for two-lane rural highways: Because of the different nature of data from each State, a different statistical analysis approach was employed for each State-an EB, before-after analysis of Kansas data, an interrupted time series analysis of Michigan data, and a cross-sectional analysis of Illinois data. Although it is well known that causation is hard to establish based on observational studies, the results from three extensive statistical analyses all led to the same findings that wider edge line pavement markings on two-lane rural highways lead to lower crash frequencies.
- Crash frequency analyses for multilane highways: Interrupted time series analyses of Michigan data and cross-sectional analyses of Illinois data were performed. The findings from these analyses do not support the use of wider edge line pavement markings for multilane highways.
- Crash severity on two-lane rural highways: This innovative analysis approach found positive safety effects for wider edge line pavement markings for two-lane rural highways, supporting the findings from the crash frequency analyses. More specifically, the findings demonstrate a shift from more to less severe crashes for two-lane rural highways with wider edge line pavement markings.
ENVIRONMENTAL CONCERNS
Environmental concerns are as follows:
- A review of past and ongoing research includes a description of a study aimed at supporting decisionmaking concerned with regulating the presence of heavy metal (specifically arsenic and lead) in recycled glass beads used in pavement marking systems.
- A discussion of LCA is included to suggest a framework that can be used to include environmental health and safety considerations in the process of selecting pavement marking products for application.
- BMPs for storage, handling, application, and removal of pavement marking materials are described.
- Recommendations are included to standardize the information present on the MSDSs accompanying products and develop specification guidelines for the storage, handling, application, and removal of pavement markings.
STATE PROCUREMENT AND BIDDING PRACTICES
Information on State procurement and bidding practices includes the following:
- In a review of State transportation department practices, it was discovered that there is a wide disparity in how agencies procure pavement markings. There is no research that conclusively demonstrates that a move to performance- or warranty-based specifications for the procurement of pavement markings will result in higher-quality installations.
- State agencies are moving to performance- or warranty-based specifications in hopes of obtaining higher-quality, longer lasting, and more effective pavement markings.
RECOMMENDATIONS FOR FUTURE RESEARCH
Despite having several objectives, this study allowed researchers to thoroughly analyze various aspects of pavement marking, including performance, safety, environmental concerns, State bidding practices. The results of the environmental portion of this study have already spurred additional research pertaining to the human health risks associated with glass beads used for pavement markings. Additional recommendations for research are as follows:
- One of the most interesting findings from this study is the estimated safety benefit, measured by expected reductions in expected crash frequency, of using wider edge lines on RTLTW highways. It is interesting because the safety surrogate study (i.e., the operational effects study) resulted in subtle differences in driver behavior when 4-inch edge lines were converted to 6-inch edge lines. Additional research is needed to better understand how the use of wider edge lines can have such a significant safety impact while not influencing traditional measures of driver behavior. Ideally, this study would involve real-time coordination between the research team and State agencies to develop a study design that includes locations of wider lines implementation, reference site locations, and real-time monitoring of other characteristics (e.g., retroreflectivity) during the course of the study. While the study would take 3 years or more to compile adequate after data, the benefits would include safety estimates with fewer caveats than the current study.
- An opportunity exists for additional research to better understand how different types of low-cost safety treatments affect different crash types and severities. This will result in more precise considerations when prioritizing their use at specific locations. For instance, it is unlikely that one could experience an additive safety impact by installing both rumble strips and wider edge lines. Do these low-cost safety treatments impact all crashes similarly, or are there some crash types that are more affected by one treatment than the other?
- This study focused primarily on the use of wider edge lines and not on wider centerlines (the Illinois data did provide the opportunity to look at 5-inch edge lines and centerlines, but within a cross-sectional study). A follow-up question that has already surfaced is, "What would be the result of increasing both the edge line and centerline width?" Similarly, would the impact on rural two-lane highways be even greater if 8-inch edge lines were used?