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Pavement Marking Demonstration Project: State of Alaska and State of Tennessee-Report to Congress

Chapter 6. Conclusions

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This report, prepared in response to requirements in SAFETEA-LU § 1907, provides a summary of findings regarding a pavement marking demonstration project carried out in Alaska and Tennessee.

Impacts of Wider Pavement Markings

Earlier crash studies conducted on wider pavement markings have been inconclusive, showing no particular benefit. The research summarized herein is based on two independent analyses of the potential benefit of wider pavement markings on rural two-lane highways-one using an EB before-after analysis and the second using a cross sectional analysis based on a binomial regression model.

• An EB before-after evaluation of crash data in Michigan resulted in positive safety effect estimates for total, F + I, PDO, daytime, daytime F + I, nighttime F + I, wet, wet night, single vehicle wet, and opposite direction crashes.
• A negative binomial regression analysis based on crash data in Illinois aggregated for 6 years resulted in positive safety effect estimates for F + I, daytime, daytime F + I, nighttime F + I, wet, single vehicle wet, and fixed object crashes.

The crash surrogate study results support previous findings, which show that there are either no real vehicle operational impacts or, at most, only subtle vehicle operational impacts as a result of adding or widening edge line markings, even for narrow two-lane highways and day and night conditions.

Cost effectiveness of Pavement Markings

The Anchorage, AK, test deck 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 was responsible for the accelerated degradation of the tape product. The only marking that maintained adequate retroreflectivity through the first two winters was the tape on the edge line. The tape was the most expensive alternative marking installed on the Anchorage, AK, test deck and required application in a groove in areas where snow plow operations were expected. If maintained retroreflectivity and presence are deemed to be necessary throughout the winter months and into the spring, then the in-laid tape marking is the only tested system that was able to achieve these performance levels for only 1 year on the lane lines.

One strategy that the DOT&PF uses is applying a durable MMA marking in a groove and remarking 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 the 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.

Two test decks were installed in Tennessee, one near Nashville and another near Tusculum. Essentially all of the markings evaluated on the Tennessee test decks continue to provide adequate presence and retroreflectivity. While the markings have not degraded at the same rate, none have reached a point where the retroreflectivity has fallen below the minimum level of 100 mcd/m²/lux established for this project. As a result, the cost effectiveness of the alternative pavement marking systems installed on the Tennessee test decks cannot be determined at this point. These markings continued to be evaluated through the 2009–2010 winter.

State Procurement and Bidding Practices

In a review of State transportation department practices, it was discovered that there is a wide disparity in how the 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 result in higher quality installations.

State agencies are moving to performance- or warranty-based specifications to obtain higher quality, longer lasting, and more effective pavement markings.

Environmental Concerns

State agencies are changing to lead-free and chromate-free thermoplastic markings, thereby satisfying the most recent environmental regulations. The latest EPA airborne lead regulation may cause a concern for agencies that try to remove lead-pigmented thermoplastic pavement markings. No research has been conducted to determine the amount of airborne lead released when encapsulated lead-pigmented thermoplastic is removed (by grinding or waterblasting).

Some multicomponent materials tested on the Alaska and Tennessee test decks are qualified as hazardous materials. Depending on the results of the Tennessee durability information and the final recommendations made from that information, there may be other environmental concerns resulting from this effort. However, the durability test decks in Tennessee are not yet old enough to make recommendations concerning specific pavement marking materials.

An evaluation of the potential environmental and health impacts of heavy metals in glass beads used in pavement markings was beyond the scope of this study. The magnitude of environmental and safety hazards of heavy metals in glass beads is somewhat uncertain. Heavy metals in glass beads do not appear to be leachable under the conditions of the EPA TCLP test which defines toxicity under current hazardous waste regulations. In fact, vitrification appears to be an acceptable method of disposing of heavy metal wastes. An ongoing project at Rowan University is studying total heavy metal levels in various batches of domestic and foreign sourced beads as well as leaching under a variety of conditions, including the presence of snow and ice control chemicals. This project will be completed in June 2010.

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