United States Department of Transportation
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Edition:Final report; Oct. 27, 2005-Apr. 30, 2009
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NTL Classification:NTL-HIGHWAY/ROAD TRANSPORTATION-HIGHWAY/ROAD TRANSPORTATION;NTL-HIGHWAY/ROAD TRANSPORTATION-Materials;NTL-OPERATIONS AND TRAFFIC CONTROLS-Traffic Control Devices;
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Abstract:This report presents an evaluation of Double Drop Bead (DDB) edge lines used on ALDOT-maintained highways. It compares DDB to three other pavement marking types in terms of service lives, life-cycle costs, and both dry-night retroreflectivity and wet-night retroreflectivity. The other three marking types are standard flat thermoplastic marking (FTM), Rumble Stripes, and profiled pavement marking (PPM).
Wet and dry retroreflectivity for the four pavement marking types was field-measured for marking ages ranging from a few months to approximately four years. The project estimated the average dry retroreflectivity of DDB to be significantly higher than the other marking types for the entire four-year test term, followed in order by Rumble Stripe, FTM, and PPM. In terms of wet retroreflectivity, DDB was again highest, followed by PPM and Rumble Stripe. A valid decay rate for wet FTM could not be established.
An estimate of the longevity of the markings generally indicates that DDB has the longest useful life on similar ADT roads, followed by Rumble Stripe, FTM, and PPM materials. The life-cycle cost analysis showed that over an eight-year life cycle, the cost per mile of marking was lowest for FTM, followed in order by DDB, Rumble Stripe, and PPM.
The Double Drop Beads edge marking exhibits the highest dry retroreflectivity of the four markings throughout the range of marking ages tested and for limited future projections. It provides this increased retroreflectivity for a relatively small increase in cost per mile. For those reasons, the report recommends that ALDOT should strongly consider making DDB edge markings its standard edge marking. However, because ALDOT has so far tested only one type of DDB marking, it should also work to optimize such characteristics as bead sizes, proportions of high refractive index beads, etc. before establishing a standard.
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