A two-layer Monte Carlo lookup table-based inverse model is validated with two-layered phantoms across physiologically relevant optical property ranges. Reflectance data for source-detector separations of 370 μm and 740 μm were collected from these two-layered phantoms and top layer thickness, reduced scattering coefficient and the top and bottom layer absorption coefficients were extracted using the inverse model and compared to the known values. The results of the phantom verification show that this method is able to accurately extract top layer thickness and scattering when the top layer thickness ranges from 0 to 550 μm. In this range, top layer thicknesses were measured with an average error of 10% and the reduced scattering coefficient was measured with an average error of 15%. The accuracy of top and bottom layer absorption coefficient measurements was found to be highly dependent on top layer thickness, which agrees with physical expectation; however, within appropriate thickness ranges, the error for absorption properties varies from 12-25%.
Very short duration maintenance operations (VSDOs) last for 15 minutes or less and usually involve operations such as removing an object from the roadway (either on the pavement or adjacent shoulder) or pothole patching. These activities have the potential to interrupt traffic flow and can pose a safety risk for both workers and drivers. Specific guidance for VSDOs is undocumented and workers tend to use their own judgment in making critical time sensitive decisions. Identifying risk factors in VSDOs helps maintenance workers better judge the immediate conditions and make more informed decisions on whether to conduct an operation as a VSDO or not. This study sought to define a VSDO and identify typical VSDOs. In addition, this study identified risk factors that maintenance workers may face during VSDOs. Moreover, this study prepared a list of technologies and methods for minimizing risk to workers in VSDOs. This study also presented a risk management process that enables maintenance workers to identify work zone hazards for VSDOs and improve their judgment about work zone conditions and hazards. Multiple scenarios illustrating the risks were presented, and related safety recommendations were also discussed. http://library.ctr.utexas.edu/ctr-publications/0-6640-1.pdf