Road studs (often referred to as ‘cat’s eyes’) reflect incident light by using a retroreflector, thus reversing the direction of visible light from vehicle headlights and returning it along a parallel path. Hence, when driving along a road at night, the road studs are visible without the need for power to light the stud.
The retroreflector may be made from glass, or plastic. The studs themselves are fixed to the road surface in a number of ways including being bonded, anchored using physical fixings or being embedded into the road surface. They may also be depressible, whereby they will deform when a vehicle drives over them but recover when the vehicle has passed.
The choice of stud used will depend on location, the ambient conditions, e.g. temperature, that it will have to endure and whether it is intended to be placed as a permanent fixture on the road surface or whether it is being used where roadworks are being undertaken and hence is only intended to be present for a limited period of time.
Regardless of the type of stud or its intended use, in the EU there are a number of requirements that must be met. These are in EN 1463 part 1: 1997 Road marking materials. Retroreflecting road studs – Initial performance requirements.
Clause 4 of this standard defines the different types of studs available according to use, reflector type and design:
• Type P – This is a permanent road stud and provides night-time warning guidance and information to road users
• Type T – This is a temporary road stud providing day and night time warning guidance and information to the road user. These types of studs are only used at construction and maintenance sites.
The materials from which the studs are manufactured are then classified as follows:
• Type 1 – Glass
• Type 2 – Plastic
• Type 3 – Plastic with abrasion resistant layer. The abrasion resistant layer is applied to the surface exposed to the traffic.
Type A or B is further used to describe whether the stud is a depressible (type A) or non depressible (type B) design.
Hence a type P1A stud is a permanent depressible stud made from glass.
The performance characteristics for the road studs are listed in clause 5 and cover requirements for the construction, including that sharp edges shall not be present on the parts of the stud that will be in contact with the tyres of vehicles. Also set are limits for the height above the road surface and the width of the studs, in relation to the direction of travel.
The visibility of the studs during the hours of darkness is quantified as both the luminance intensity (how bright the stud is) and also the colour of the stud. The luminance is measured at different light entrance and observation angles to ensure that the item is visible from a range of directions, whilst the colour is defined as X and Y coordinates within the normal colour sphere.
For temporary road studs a requirement for the daytime visibility of the stud is also given as a defined colour. It should be noted that all the performance requirements for road studs are based on the product in its new condition and do not take into account how use of a product or how the road or other external conditions will affect it.
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Retroreflective road studs on test
Permanent and temporary retroreflective road studs come under the Construction Products Directive for performance testing.
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SATRA is a Notified Body for the Construction Products Directive and is able to provide testing facilities that are UKAS-accredited for the performance testing of road studs and other construction products. For further information on the services offered by SATRA, please contact Jackie Glasspool (jacqueg@satra.co.uk).
