This paper presents a conventional approach for assessing highway visibility at night in foggy weather, based on the Visibility Level (VL) concept. The method is adapted from a nighttime visibility assessment method published earlier. First, we recall the basics of the VL concept and the associated target visibility computation model. We also recall the conventional obstacle collision scenario which serves to estimate the nighttime visibility distance as a function of pavement retroreflectivity for a given headlamp beam pattern, using the basic laws of photometry. Then we introduce the visibility impairing effects of fog. The first effect is the exponential attenuation of luminance with distance, described by Beer-Lambert law. The second effect is the veiling luminance gener ated by the backscattering of headlight, for which we propose an empirical model based on physically-based simulations. We apply the presented approach to low-beam and high-beam patterns in different fog conditions, and we bring quantitative proof for the need to dip the headlamps in dense fog. The assessment of the nighttime visibility distance can be combined with the notion of atmospheric visibility in order to predict the visibility range when driving in different fog conditions at night. Recent evolutions in the regulations concerning automotive lighting systems such as have lead to proposals such as tending to a more common use of "highbeams type" lighting systems. This interesting proposal should nonetheless be investigated knowing that in certain meteorological conditions the appropriate answer may be elsewhere as was shown for dense fogs. Embedded fog detection systems, for instance, may provide useful input to future adaptive front-lighting systems. The visibility metering tool may also be used to help road operators anticipate visibility reduction depending on the weather, and thus adapt posted speed limits dynamically (by means of changeable message signs or with future cooperative systems). Finally, the issue of seeing the road at night in absence of public lighting is a general problem, but more so for some populations such as elderly people. Age being a parameter of Adrian's model, this tool could be helpful to characterize the distribution and deviation of visibility supply on a road network among drivers and take safety measures or adapting lighting systems to these problems.


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    Title :

    A conventional approach to nighttime visibility in adverse weather conditions


    Additional title:

    Eine konventionelle Annäherung an nächtliche Sichtverhältnisse bei widirgen Wetterzuständen


    Contributors:


    Publication date :

    2011


    Size :

    12 Seiten, 4 Bilder, 20 Quellen



    Type of media :

    Conference paper


    Type of material :

    Print


    Language :

    English




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