Impacts of Fog Characteristics, Forward Illumination, and Warning Beacon Intensity Distribution on Roadway Hazard Visibility

Abstract

Warning beacons are critical for the safety of transportation, construction, and utility workers. These devices need to produce sufficient luminous intensity to be visible without creating glare to drivers. Published standards for the photometric performance of warning beacons do not address their performance in conditions of reduced visibility such as fog. Under such conditions light emitted in directions other than toward approaching drivers can create scattered light that makes workers and other hazards less visible. Simulations of visibility of hazards under varying conditions of fog density, forward vehicle lighting, warning beacon luminous intensity, and intensity distribution were performed to assess their impacts on visual performance by drivers. Each of these factors can influence the ability of drivers to detect and identify workers and hazards along the roadway in work zones. Based on the results, it would be reasonable to specify maximum limits on the luminous intensity of warning beacons in directions that are unlikely to be seen by drivers along the roadway, limits which are not included in published performance specifications.

Toward performance specifications for flashing warning beacons

“…Also, as mentioned previously, the ideal intensities for driver guidance through a work area were not studied, so the proposed performance specifications are strictly limited to the detection of warning beacons. The present studies also simulated clear, dry roadway conditions, and the presence of rain or fog (Bullough and Rea, 2016) might warrant different nighttime intensities than those recommended in Table 2 (e.g., because of scattered light in the atmosphere). Further, the proposed upper limit might not be ideal for, say, sunny days where the ground is covered with snow.…”

Benchmarking Image Sensors Under Adverse Weather Conditions for Autonomous Driving

“…Attenuation which involves scattering and luminescence [11] describes the loss of emitted light for the observer. For smaller and simpler scenarios, exact Monte Carlo simulations can be used [12]- [14]. However, such a method is very extensive.…”

The effect of fog on detection of driving hazards after dark

“…Droplet size matters because it affects how light is scattered, and hence how well it simulates the effect of fog on scattering which is largely insensitive to wavelength. 22 For larger droplets, Mie scattering is predominant which is not significantly affected by wavelength, but for smaller droplets then Rayleigh scattering becomes more significant, and this is affected by wavelength. 30 Mie scattering is expected when droplet radius (here the smaller median droplet size has radius 0.1 mm) is greater than 0.1 times the wavelength of light (here 0.07 mm for long wavelength light at 700 nm) 31 : this suggests the droplets used in this fog simulation adequately represent the light scatter of real fog.…”