INFLUENCE OF PAVEMENT SURFACE CHARACTERISTICS ON NIGHTTIME VISIBILITY OF OBJECTS

Vehicle headlights do not light enough of a roadway length for safe nighttime driving at higher driving speeds. Therefore, particularly on highways with high traffic levels, fixed roadway lighting enables safe nighttime driving conditions. Roadway lighting design has evolved over the years from the illumination method, which is based on the amount of light falling on the road surface, to the luminance- and visibility-based methods that are in use today. Visibility of an object on the roadway is directly related to the contrast between the object and its surroundings. In nighttime driving situations, the pavement acts as the background for most objects on the road. Therefore, reflectance characteristics of the pavement are important in visibility-based roadway lighting design processes. Currently, pavement reflectance characteristics are incorporated through four standard reflectance tables (r-tables) developed to represent portland cement concrete, open-graded asphalt concrete, seal coat, and dense friction coarse asphalt pavements. In this research, the computer program STV developed by M.E. Keck, which calculates pavement luminance and visibility level, was used for a sensitivity analysis to evaluate how the pavement type and the standard r-tables influence these parameters. The analysis was conducted for fixed roadway lighting situations without the influence of vehicle headlights. Results from the sensitivity analysis indicated that standard r-tables are not sufficient to model the whole spectrum of pavement surfaces encountered in practice. An analysis of pavement reflectance data collected by the Road and Transportation Association of Canada revealed that asphalt-based pavements tend to increase their specularity and brightness with age, whereas portland cement concrete pavements display a decreasing trend

DIII-D research advancing the physics basis for optimizing the tokamak approach to fusion energy

Funding Information: This material is based upon work supported by the US Department of Energy, Office of Science, Office of Fusion Energy Sciences, using the DIII-D National Fusion Facility, a DOE Office of Science user facility, under Awards DE-FC02-04ER54698 and DE-AC52-07NA27344. Publisher Copyright: © 2022 IAEA, Vienna.DIII-D physics research addresses critical challenges for the operation of ITER and the next generation of fusion energy devices. This is done through a focus on innovations to provide solutions for high performance long pulse operation, coupled with fundamental plasma physics understanding and model validation, to drive scenario development by integrating high performance core and boundary plasmas. Substantial increases in off-axis current drive efficiency from an innovative top launch system for EC power, and in pressure broadening for Alfven eigenmode control from a co-/counter-I p steerable off-axis neutral beam, all improve the prospects for optimization of future long pulse/steady state high performance tokamak operation. Fundamental studies into the modes that drive the evolution of the pedestal pressure profile and electron vs ion heat flux validate predictive models of pedestal recovery after ELMs. Understanding the physics mechanisms of ELM control and density pumpout by 3D magnetic perturbation fields leads to confident predictions for ITER and future devices. Validated modeling of high-Z shattered pellet injection for disruption mitigation, runaway electron dissipation, and techniques for disruption prediction and avoidance including machine learning, give confidence in handling disruptivity for future devices. For the non-nuclear phase of ITER, two actuators are identified to lower the L-H threshold power in hydrogen plasmas. With this physics understanding and suite of capabilities, a high poloidal beta optimized-core scenario with an internal transport barrier that projects nearly to Q = 10 in ITER at ∼8 MA was coupled to a detached divertor, and a near super H-mode optimized-pedestal scenario with co-I p beam injection was coupled to a radiative divertor. The hybrid core scenario was achieved directly, without the need for anomalous current diffusion, using off-axis current drive actuators. Also, a controller to assess proximity to stability limits and regulate β N in the ITER baseline scenario, based on plasma response to probing 3D fields, was demonstrated. Finally, innovative tokamak operation using a negative triangularity shape showed many attractive features for future pilot plant operation.Peer reviewe