Bonded road studs

A non-depressible bonded road stud is rectangular in plan and comprises a body portion having a substantially flat upper face and four substantially upright side faces sloping downwardly from the side edges of the upper face onto a basal plinth portion. The basal plinth extends laterally away from the lower edges of the upright side faces of the body portion on all sides thereof and has an upper surface sloping outwardly and downwardly away from the periphery of the body portion. Two opposite upright side faces of the body portion are fitted with reflecting lenses and the upper surfaces of the plinth adjacent the lens-carrying side faces of the body portion comprise ridges which are substantially centered with respect to the side faces and the said upper surfaces are cambered to slope away from both sides of the ridges. The plan area of the road stud is at least 70% greater than the plan area bounded by the periphery of the body portion and the average thickness of the basal plinth is substantially 10% to 20% of the maximum thickness of the stud.

This invention relates to bonded road studs. 
The use of road studs, and in particular reflecting road studs, in order to 
warn, guide or inform road users is well known. More recently reflecting 
non-depressible road studs which are bonded to the road surface, rather 
than anchored within the road surface, have been gaining favour. Such 
studs, manufactured in a plastics material, have been found to comply with 
relevant requirements. 
A bonded, reflecting non-depressible road stud is adhesively bonded to the 
road surface. Asphalt or coated macadam is a road material in common use, 
and suitable adhesives for bonding studs to the surface of a road of such 
material, as well as to concrete roads, have been developed. The preferred 
technique of laying such studs is to apply a layer of adhesive, which may 
be based on epoxide resin, to the road surface and press the stud firmly 
into the adhesive so that adhesive is squeezed out around the sides of the 
stud to form a seal around the edge, the stud being bedded in the layer of 
adhesive. 
Both the epoxide adhesive and asphalt or coated macadam road materials are 
thermoplastic in nature, and therefore have a tendency to soften when 
heated. During a hot summer, road surface temperatures of 130.degree. F. 
or more can be encountered. It has been found that the softening which the 
adhesive and the road material undergo when road surface temperatures of 
this level are reached, can result in the road traffic passing over the 
studs impacting the studs into the road surface, with subsequent break-up 
of the adhesive bond and detachment of the studs. 
It is an object of this invention accordingly to provide an improved road 
stud which is less subject to detachment from the road surface under 
extreme temperature conditions. 
The present invention proposes accordingly to provide a non-depressible 
bonded road stud which comprises an upstanding body portion and a basal 
plinth portion extending laterally away from the periphery of the body 
portion on all sides thereof. 
The provision of the basal plinth enlarges the effective surface area of 
the stud for bonding to the road surface and results in loads applied 
externally to the stud being distributed over a greater area of the road 
surface so lessening the degree of penetration of the stud into a 
thermoplastic road surface which has become softened due to the effects of 
extreme ambient temperatures. This advantageous effect arises because of 
the reduction in load per unit area at the stud/road surface interface due 
to the provision of the basal plinth which increases the base area of the 
stud at the interface. 
The road stud may be of monolithic or composite construction. A composite 
construction may provide a relatively thin rolled outer skin or shell 
construction the interior of which is filled with a suitable filler 
material. However, the plinth is preferably comprised by a base flange 
integral with a body portion of the road stud, although it may be 
initially formed separately and thereafter bonded to the body portion of 
the stud. The body portion of the stud preferably includes reflectors 
which may be of any suitable type as bi-convex lenses or cube-corner 
reflecting elements. The upper surface of the road stud is preferably 
uneven, to confer skid resistance. The road stud may be constructed of a 
suitable plastic material, natural or synthetic rubber.

Referring to the drawings, the road stud shown, which may be integrally 
moulded from acrylonitrile butadiene styrene copolymer, comprises an 
upstanding body portion 1 and a basal plinth portion 2. The body portion 1 
comprises the portion of the stud within the peripheral or boundary line 
3, and the plinth 2 surrounds the body portion 1 on all sides and extends 
laterally away from the periphery 3 thereof. 
The outer boundary of the road stud is substantially rectangular in plan, 
whereas the body portion 1 is substantially square and is centered on the 
plinth 2. The central body portion 1 has opposite pairs of substantially 
upright side faces 4 and 5 and an upper substantially flat face 6. All 
edges and corners of the upper surfaces of the road stud are rounded so as 
not to present any sharp edges to road traffic and at least the upper face 
6 may be superficially roughened, for example by being imprinted. 
Two opposite side faces 4 of the stud main body portion 1 are provided with 
reflecting lenses 7 which are permanently sealed into the body of the 
stud. Two rows of reflecting lenses are shown, but more or fewer could be 
provided. 
The upper surface of the plinth 2 slopes outwardly and downwardly away from 
its line of juncture with the main body portion 1 at the periphery 3 to 
allow rain water and mud to run off. In addition, the upper surfaces of 
the plinth adjacent the lens-carrying faces 4 are cambered to fall away 
sideways as well as outwardly, see particularly FIGS. 2 and 3, from 
respective high points or ridges 8 substantially centered with respect to 
the faces 4. This provides an additional "lead-in" for road traffic 
running over the stud and also improves drainage from the faces 4, 
particularly under adverse weather conditions, and thus assists in 
preventing soiling of the lenses 6. 
Typical dimensions of the improved road stud shown and described are as 
follows: 
Overall dimensions of the stud in plan--140 mm.times.120 mm. 
Overall thickness (height) of stud--17 mm. 
Average thickness of plinth 2-1.75 mm, rising to 3.5 mm at the ridges 8. 
In comparison with a conventional road stud having overall dimensions 
substantially that of the main body portion within the boundary 3 of 
approximately 101 mm.times.98 mm, the exemplary improved road stud 
according to the invention shown and described has a surface area for 
bonding to the road surface approximately 70% greater. Impact tests made 
with the improved road stud shown and described in comparison with the 
aforesaid conventional stud to assess the penetration characteristics of 
both studs into a thermoplastic material by measuring the depth to which 
both road studs penetrate the material at the same temperatures and loads 
have shown that the ratio of the depth of penetration of the improved road 
stud into a thermoplastic medium to the depth of penetration of the 
conventional road stud is of the order of 1:4, and there is evidence to 
show that this ratio will increase over an extended period of use. 
It will be appreciated that the improved road stud according to the 
invention may be designed in other ways from that specifically described 
and illustrated and still fall within the scope of the appended claims.