Retro-reflectivity

The key to a good Road Marking is optimum retro-reflectivity, this is now one of the key performance parameters in current road marking specifications.

To obtain good retro-reflectivity, several elements are needed:

• Good quality round beads
• Optimum bead embedment
• A bright white background for the beads

How Does Retro-reflectivity work?

A glass bead works by reflecting the light from a vehicle's headlights back to the driver. Retro-reflectivity is usually measured in mcd/lx/munits (millicandella per lux per square metre), which is a measure of efficiency of the glass beads within the marking to return light to its source (vehicle headlights). Some of this light will be reflected back to the driver.

In simple terms retro-reflectivity is a ratio of the light visible to the driver compared to the light entering the marking and the more efficient the material is, the brighter the marking will appear.

Under the new European Standards for road markings that are based on performance for the end-user (the driver). Local Authorities will often specify the particular level of retro-reflectivity that is required dependent on local road conditions. For example retro-reflectivity may be specified at a higher reflective level in accident black spots.

When a road marking is first laid, unless the line is dowsed with extra glass beads, the in-mix beads (Class A, Beads) are completely surrounded by thermoplastic material.

Glass beads give the best retro reflectivity when 40% of its mass protrudes from the surface of the road marking material. Less than this and efficiency will be lost and more than this will mean a high initial loss of beads from the line.

As the road marking is worn by traffic the in-mix beads, are gradually uncovered, this process can take some time, particularly in the case of edge lines or where traffic volumes are low. Generally in these instances surface beads are applied (Class B, Beads) to ensure initial retro-reflectivity.

Good retro-reflectivity improves night visibility for drivers. In dark, wet conditions standard road markings disappear, as the light that is normally reflected back to the driver is scattered in all angles due to the film of water on the surface of the line.

50% of all reported road traffic accidents at night occur in wet conditions. Yet in the UK it is wet only 10% of the night!

Specialist wet night visibility road markings are now available on the market, the use of larger glass beads and innovative application methods have overcome the problems of rain water flooding the line and therefore making it disappear.