Warm-mix asphalt (WMA) describes a range of technologies that seek to lower emissions and reduce energy consumption by lowering the temperature at which asphalt mixtures are produced and placed. Despite these benefits, reduced mixture viscosity may be the most likely reason for widespread adoption of WMA technologies. Hot-mix asphalt (HMA) producers are unlikely to adopt WMA technologies solely to lower emissions, because current environmental regulations and the relatively clean nature of HMA plants make lower emissions unnecessary and unprofitable except in select air pollution areas. Producers are also unlikely to adopt WMA technologies solely to reduce energy consumption, because energy savings are less than the associated costs except in the most expensive energy markets. Reduced viscosity makes the best business case for widespread WMA technology adoption, because this benefit offers cost and risk reduction: it can (a) alleviate compaction problems associated with cool weather, (b) reduce compaction equipment needs at the job site, and (c) lower the risk of poor compaction when working with stiff mixtures. This conclusion is supported by basic economic calculations, a survey of the Icelandic pavement industry showing strong support for WMA technology use to improve cool weather paving, and two projects in Maryland showing the potential for WMA technology use to lower the risk of poor compaction of high reclaimed asphalt-pavement mixtures.

Greenroads ( www.greenroads.us ) is a performance metric for sustainable practices associated with the design and construction of roads. It assigns points for approved sustainable choices/practices and can be used to assess roadway project sustainability measures based on total points. Such a metric can (1) provide a quantitative means of sustainability assessment, (2) allow informed sustainability decisions, (3) provide baseline sustainability standards, and (4) stimulate improvement and innovation in integrated roadway sustainability. This paper describes Greenroads version 1.0, which consists of 11 requirements and 37 voluntary practices that can be used as a project-level sustainability performance metric. Development efforts and a Washington State Department of Transportation (WSDOT) case study suggest (1) existing project data can serve as the data source for performance assessment, (2) some requirements and voluntary actions need refinement, (3) projects need to treat sustainability in a holistic manner to meet a reasonable sustainability performance standard, (4), the financial impact of Greenroads use must be studied, and (5) several pilot projects are needed. The Greenroads sustainability performance metric can be a viable means of project-level sustainability performance assessment and decision support.

Each year the United States places about $100 billion of roadway construction. This level of activity suggests possibly significant sustainability implications in the construction activities for this work. One means to quantify some of these impacts is through life-cycle assessment (LCA). A review of 14 roadway construction LCA papers reveals some common ideas about the ecological impacts of roadway construction. Some key observations are that (a) the energy expended during roadway construction is roughly equivalent to that used by traffic operating on the facility for 1 or 2 years, (b) total energy use during roadway construction varies but is typically on the order of 3 to 7 TJ/lane mile, (c) total CO2 emissions during roadway construction vary but are typically 200 to 600 Mg/lane mile, (d) materials production makes up 60% to 80% of energy use and 60% to 90% of CO2 emissions associated with construction, (e) construction activities at the jobsite make up less than 5% of energy use and CO2 emissions, and (f) transportation associated with construction makes up 10% to 30% of energy use and about 10% of CO2 emissions associated with construction.

Numerous Washington State Department of Transportation (WSDOT) paving projects have experienced a cyclic occurrence of premature failure of open-textured asphalt concrete (AC) pavement sections by fatigue cracking, raveling, or both, generally called “cyclic segregation” or “endof-load segregation.” This resulted in an initial study in which mat temperature differentials were observed during laydown. In turn, this led to the current study and the reported results. Pavement temperature differentials result from placement of a cooler portion of the hot-mix mass into the mat. This cooler mass generally constitutes the crust, which can develop during hot-mix transport from the mixing plant to the job site. Placement of this cooler hot mix can create pavement areas near cessation temperature that tend to resist proper compaction (they may also exhibit tearing or roughness or appear to be open textured). These areas were observed to have decreased densities and a higher percentage of air voids (higher air voids). Four 1998 WSDOT paving projects were examined to determine the existence and extent of mat temperature differentials and associated material characteristics. An infrared camera was used to identify cooler portions of the mat, which were then sampled along with normal-temperature pavement sections. Gradation and asphalt content analysis showed no significant aggregate segregation within the cooler areas. However, these cooler portions of the mat consistently showed higher air voids than the surrounding pavement. On the basis of numerous studies that have related AC deterioration and high air voids in a mix, it is known that the areas of a mat with higher air voids may experience premature failure compared with the time to failure of the mat as a whole.

Greenroads, a system used to rate the sustainability of roadway projects, was used to evaluate 105 roadway and bridge projects in the United States for sustainable design and construction practices at various life cycle stages. A sustainability rating system can be a practical tool to help quantify and measure sustainability for a roadway project. The purpose of the investigation was to determine the state of the practice in sustainable roadway design and construction by application of Greenroads to a variety of actual projects. Forty projects identified as sustainable were compared with 65 typical projects representing conventional practice. The objectives of this study were to (a) identify trends in Greenroads project ratings, (b) benchmark the current state of the practice and identify potential areas for improved sustainability performance, (c) determine whether Greenroads can differentiate among projects on the basis of their sustainability efforts, and (d) identify the implications of these findings to practice. The results show that (a) some credits and categories are easily achieved, although achievement of others is more challenging and offers opportunities for improved environmental performance; (b) typical roadway projects tend to meet environmental regulatory standards but rarely do much more even when possible; therefore, they score fewer points for credits that focus on environmental benefits beyond the regulatory minimum; (c) contractors and materials suppliers appear to have unrealized opportunities to contribute; and (d) an early emphasis on the environment during project development appears to differentiate between typical and sustainable projects and manifest as higher Greenroads scores.