Coatings World - November 2015

By Mike Kaufman, Senior Applications Development Leader, Arkema Coating Resins

Abstract

White and yellow traffic markings, used for the demarcation of traffic, are a common sight on most roads. In North America the majority of traffic markings are applied as paint to the road surface.

Before traffic marking paint can be approved for use it must be submitted for evaluation to ensure that it conforms to federal and/or state specifications. Testing includes the application of transverse traffic marking to test decks exposed to a high volume of vehicular traffic and the elements, as part of the National Transportation Product Evaluation Program (NTPEP), and may last as long as three years.

In an effort to reduce the time and cost associated with developing higher performance traffic marking paints, abrasion resistance has been proposed as an accelerated method for evaluating the durability of traffic markings. It is a simple and inexpensive technique which yields highly reproducible results in a short period of time. These results correlate well with available NTPEP test deck retroreflectivity and durability ratings.

Abrasion resistance testing suggests that traffic markings with 3 year durability could be achieved with a 15 wet mil line if a high durability latex binder was employed in the traffic marking paint formulation.

White and yellow traffic mark- ings, used for the demarcation of traffic, are a common sight on almost all roads. These markings enhance driver safety under varying weather and lighting conditions by continuously providing drivers with information concerning vehicle speed, lane delineation, road direction, warnings about upcoming conditions, and indications of where passing is allowed.

The daytime visibility of traffic markings relies on the color contrast between the marking and the road deck. Color contrast alone is inadequate to ensure acceptable night time visibility. Instead, embedded glass beads function as retro-reflective elements reflecting light from vehicle headlights. Over time, mechanical abrasion by vehicles reduces traffic marking performance by damaging or dislodging beads and ultimately removing the markings from the road deck.

In North America the majority of
traffic markings are applied as paint to
the road surface. Before traffic marking
paint can be approved for use it must be
submitted for evaluation to ensure that
it conforms to federal and/or state speci-
fications. Specifications for pavement
markings usually consist of some com-
bination of chemical composition and
performance requirements. The cost and
availability of some chemical components
used in paint manufacture vary dramati-
cally and, as a result, detailed composi-
tion specifications favored by highway
agencies in the past are being replaced by
performance specifications. In some cas-
es, a combination performance-composi-
tion specification is used which indicates
the percentage by weight of each ingre-
dient, by generic classification, without
specifying a brand name or chemical for-
mula. Performance testing involves the
application of transverse traffic marking
to test decks exposed to a high volume of
vehicular traffic and the elements, as part
of the National Transportation Product
Evaluation Program (NTPEP), and test-
ing may last as long as three years.

Once a traffic marking has demonstrated its conformance with the specification, it is included on federal and state approved product lists (APLs). Traffic marking manufacturers with products on an APL can then bid on projects.

This testing process was designed to ensure that all traffic markings meet a minimum quality level and has been very effective in achieving this objective, but it has also had several unintended consequences. The relatively high cost associated with sample submission has resulted in only a limited number of test paints being placed on the test deck every year. Compositional restrictions have limited the paints to a very narrow formulation window which, when coupled with the long testing cycle, has substantially constrained the development of new technology. The net effect is that overall product performance has not dramatically increased and potential enhancements for