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Night Visibility

Night visibility, otherwise known as retroflexion, describes the demands placed on a road surface at nighttime.

Night visibility is measured by the coefficient of reflected luminance (RL) and must be measured on dry, clean markings.

RL describes the brightness of road markings in terms of their night visibility and how this is experienced by the driver of a vehicle when they shine their headlights on the markings.

Night visibility is the main field of application for type II markings because they guarantee superior visibility even in wet weather.

In this respect, they are generally preferred over type I markings and should not to be used on short stretches. In the interests of night visibility, they should be used on longer stretches, between junctions for example. Federal highways, dual carriageways, main roads and frequently used national roads and state roads all favour the use of type II markings.

Where markings are to be laid for better night visibility, they should have strong retroflective properties. This might take the form of systems that use coarse drop-on materials or those that use coarse particles. Alternatively, profiled systems and agglomerates may be used.

Glass beads are best embedded at a depth of 50–60% in order to ensure optimum reflectivity.

If glass beads are embedded too deep, most of the light from the headlight will refract into the part of the bead beneath the road surface.

 

Glass beads embedded too shallow will cause the light to pass through the bead.

Care should be taken to ensure that the glass beads are optimally spaced apart to ensure sufficient distance between the individual beads. Too many glass beads will result in many of the beads being in the shadow of those in front of them, a less than optimal distribution that will fail to efficiently improve night visibility.

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