Environment, Road & Weather

Studies where the road itself and the conditions on it are the variable: geometry, intersections, work zones, traffic, surface, weather.

What's here. Road and roadside features treated as the condition under study: road_geometry, intersection_design, road_complexity, road_surface_friction, urban_rural_setting, work_zones, and rail_grade_crossings. Also the conditions layered onto that road, traffic_density and weather_rain_fog_snow, and the markings and treatments meant to change how drivers read it, perceptual_countermeasures and signage_environment.

What isn't here.

• how far away a sign can be read, and how visible work zones, workers, or emergency vehicles are — Visibility & Lighting. signage_environment and work_zones here cover sign content and placement, work zone layout, and traffic control. Legibility distance, retroreflectivity, roadway lighting, and glare sit in the sibling category.
• speed limits, speed cameras, and enforcement programs — Policy & Enforcement. perceptual_countermeasures here covers pavement markings and roadside treatments intended to alter speed through what the driver sees. The regulatory and enforcement side of speed is filed under policy and enforcement.
• the driver's own control actions, such as speed choice, following distance, and lane keeping — Driver Behavior. This category indexes the environment as the manipulated condition. When the outcome of interest is the resulting control input rather than the road or weather producing it, look under driver behavior; a single study can be relevant to both.