Reflective Traffic Signs
Railroad Crossing Signs
Reflective glass beads, known as catseyes, magnify the visibility of this railroad crossing sign.
Optimum placement of reflective traffic signs
Retroreflective signs are illuminated for the human eye when the entrance angle..

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The science behind reflective traffic signs
What are reflective traffic signs and what is their importance? Elaborate on how these

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The science behind reflective traffic signs

Retroreflectivity is simply the return of light from a surface back to the source of light.

Retroreflection relies on three principles:

  • Specular reflection occurs when light strikes a mirror or polished surface.

  • Refraction occurs when light changes direction passing from one medium to another.

  • Total internal reflection occurs when light hits the surface of a transparent material at certain angles and reflects the light source without the light passing through the medium.

On the roads at night, the most readily available source of light is a car's headlamp, and since the headlamp is not constant but moving, its angle in relation to the sign changes as it approaches and moves away from it.

The entrance angle occurs as light strikes the surface of the sign perpendicular to it and as the car approaches a sign, increasing or widening the angle with lower retroreflectivity.

The observation angle is the angle between the illumination path (from a headlight to the sign) and the observation path (from driver eye to the sign). This is the measure of separation of the driver's viewpoint from a headlight.

Evolution of reflective traffic signs

In 1939 Harry Heltzer designed the first reflective sheeting material at 3M. In 1944, also at 3M, researchers developed new beads that reflected more light and were more weather resistant.

The development of engineer grade sheeting followed, with improved glass bead materials and high intensity grade sheeting in the 1970s. This grade doubled the return of incident lighting to 16 percent.

Prismatic optics were developed starting in 1963 by the Rowland Brothers, which led to the use of microprismatics that are being used today.

According to REMA, the Retroreflective Equipment Manufacturers Association, "This was the biggest advance in retroreflective sheeting since 3M's Engineering Grade. The molding of tiny high accuracy and high definition cube-corners, only 0.15mm to 0.25mm across meant that for the first time the highly reflective prismatic optic could be incorporated into a very thin gauge sheet of flexible transparent plastic material such as vinyl or polyester."

3M began manufacture of its own microprismatic materials called diamond grade reflective sheeting in 1988 and improved them in the 1990s.

Improvements in standards for nighttime driving

The FHWA believes unconditionally in the efficacy of retroreflective signs especially for nighttime drivers: "Providing retroreflective delineation and signing is important as a means of reducing the higher nighttime crash rates. Signs that have sufficient retroreflectivity during nighttime conditions are especially beneficial to older road users."

Concept of retroflectivity, glass bead and microprismatic technologies

Glass bead technology has evolved towards the use of microprismatic materials. Microprismatic reflective materials consist of prisms embedded into the structure of the sheeting.These prisms then reflect light where the light enters the prism and reflects off multiple faces of the prism and is then returned to the light source.

The cone of light takes on new functions where light can be distributed to areas in the cone where it is most likely to be useful to the driver or application. The advantage of microprisms over glass bead technology again doubles the returned light, just as improvements in glass beads doubled these factors with the introduction of high intensity glass beads. Microprismatic sheeting has produced returned light values up to 32 percent in recent years.

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