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UCPRC Life Cycle Assessment Methodology and Initial Case Studies for Energy Consumption and GHG Emissions for Pavement Preservation Treatments with Different Rolling Resistance

  • Author(s): Wang, T.;
  • Lee, I. S.;
  • Harvey, J.;
  • Kendall, A.;
  • Lee, E. B.;
  • Kim, C.
  • et al.
Abstract

This report describes a pavement life cycle assessment (LCA) model developed to initially evaluate total energy use and greenhouse gas (GHG) emissions from pavement maintenance and rehabilitation (M&R) strategies. This LCA model allows analysis of the energy consumption and GHG emissions associated with material production, construction, and vehicle operation during pavement use, which includes the effects of pavement roughness and texture on vehicle operation; at this time the model does not include the effects of pavement deflection. Other types of treatments and the materials used for them, as well as other effects of the pavement on the environment in the pavement Use Phase will be considered in future studies. The model was used to evaluate four case studies of Caltrans pavement preservation treatments for both asphalt and concrete surfaces with different roughness and texture and traffic levels. The case studies were performed to provide a preliminary indication of the net effect of changing the roughness and texture on the analysis period performance of pavements, not to compare asphalt and concrete pavements. At this time, asphalt and concrete pavements cannot be directly compared because submodels are not yet included in the LCA model for factors in the Use Phase other than roughness and texture. For this reason, it was assumed that the pavement preservation treatments would not change the pavement structure type (asphalt or concrete). Energy and GHG-emissions savings from pavement preservation treatments with CAPM treatments as an example (CPR B involving diamond grinding with 3 percent slab replacements for concrete and pavement preservation overlays for asphalt, performed using nighttime closures) were then compared with an alternative strategy where no treatment occurs, except for routine maintenance of damaged pavement. A preliminary indication of the sensitivity of the case study results to the level of smoothness achieved during pavement preservation construction was evaluated. A preliminary indication of the sensitivity of the net effect on GHG emissions and energy use to the level of traffic in the Use Phase was also evaluated by inclusion of a high and a low traffic case study for both concrete and asphalt pavements. The potential benefits of the treatments are also compared with energy and emissions savings from projected improvements in vehicle fleet fuel economy and reductions of vehicle miles traveled, which are strategies adopted by the California Air Resources Board for reducing GHG emissions. For highways with high traffic volumes, results of the case studies show that the energy and GHG savings accrued during the Use Phase (due to reduced roughness and macrotexture change) can be significantly larger than the energy use and GHG emissions from material production and construction. The extent of the benefit was dependent on constructed smoothness with a much smaller benefit from change of texture. These savings can be larger than those from other strategies meant to reduce highway transportation energy use and emissions for a given route, such as projected improvements in fleet average vehicle fuel economy within the period analyzed for the project location, depending on the amount of traffic using the pavement. For low traffic volume highways, the smoothness obtained by the contractor and the materials used determine whether the net effect on GHG emissions and energy use is positive or negative, and may result in a net increase in energy use and GHG emissions if low traffic volumes and poor construction quality (rough pavement produced by construction) occur together. These initial case studies only represent example sections, and application of the LCA model to the network remains to be done. The materials datasets for the case studies used data from several sources outside California that were adjusted to California electrical energy supplies. Sensitivity analysis with the different data sets did not change the conclusions. All materials mix designs (taken from meetings with industry) and construction were representative examples. The method used to combine pavement characteristics (IRI and texture) and emissions models has not been validated, although the fuel economy models have been validated by Michigan State University. This report was reviewed by concrete and asphalt industry experts through their respective California industry organizations, and errors and omissions in the original draft have been addressed based on those comments, which are gratefully acknowledged.

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