This project will develop and test biochar amendment to roadway soils across a wide range of geographic locations to increase soil aggregation, stormwater infiltration, and runoff reduction. Stage 1 work focuses on laboratory measurements to evaluate the effect of biochar amendment on soil aggregation and stormwater infiltration. Coordinating with California, Delaware, and North Carolina DOTs and Maryland Transportation Authority, roadway sites will be selected and roadway soil samples collected. Laboratory tests will be conducted over a 6-10 month period to assess if biochar amendment increases soil aggregation and infiltration, and if so, by how much, for representative soils. These data will be used to develop guidelines for biochar application. A pilot-scale highway greenway was designed and constructed at the University of Delaware Greenhouse in the previous IDEA project (NCHRP-182). In this Type 2 project, the pilot-scale experiments initiated in the previous IDEA project will be continued for two years to quantify time-dependent changes of biochar amendment on stormwater treatment. Effort in Stage 2 will focus on synthesizing the results from Stage 1 laboratory work with field data from an ongoing investigation at a roadway site in Delaware. These data will be used to develop an engineering and construction cost analysis and preliminary specifications for DOTs to incorporate biochar in roadway soils. The laboratory/pilot-scale experiments conducted in Stage 1 will provide a fundamental understanding of the influence of biochar amendment on time-dependent soil aggregate formation and hydraulic properties for a range of representative roadway soils. Field-scale measurements will be conducted to document the long-term (> 1-2 year) effects of biochar on hydraulic properties. These data are necessary to estimate the frequency of biochar replacement. An Engineering and Construction Costing Analysis will be expanded from the work completed in the previous IDEA study (NCHRP-182), which used only HSG ‘B” soils, to include HSG ‘A’, ‘B’, and ‘C’ for four different regions in the US to determine the overall constraints, benefits and cost implications including operations and maintenance of biochar-amended highway greenways. A draft final report will provide all relevant data, findings, and conclusions along with recommendations on biochar use and preliminary specifications for its selection and application.