The main requirements of the standard are:
150 minimum diameter holes in grid supports to permit escape.
150 - 200mm wide escape ramp at a maximum slope of 1 in 2. Orientated in-line with grid bars.
Grid should be positioned > 18m from a junction, and the approach clearly visible.
Lateral gradients should be > 1 in 40.
Longitudinal gradients should follow the road plane and should be < 1 in 20.
British Standard materials should be used. In particular, standards for concrete, masonry, aluminium, timber and steel including plating standard are specified.
The materials and finish should not be liable to cause injury, i.e. smooth and non toxic.
The minimum 'jump' length is 2.6m, for deer this should be > 4.0m.
The width of the grid should be the same as the road and > 2.75m.
The depth of the pit should be > 300mm.
The spacing of the grid bars should be > 130mm and < 150mm.
The flat part of the top surface of the grid bars should be < 40mm.
The spacing of grid supports should be > 300mm.
The top of the grid supports should be deeper than 40mm.
The exposed part of any grid support should be < 40mm.
> 50 Years
Department of Transport Standard for bridge loads, BD37/88 is applicable. To allow for dynamic loading effects, designs for highway use should be increased by a factor of 2. Designs for agricultural use should be increased by a factor of 1.5.
The grid deflection between supports should be < 1 percent.
Hard surfacing should extend across the full width and by > 2m in length on both sides.
The approach should lie in the same plane as the grid.
Required.
Hazard warning to BS 873 required on public roads.
Reflectors fitted to guard rail end posts.
Guard fences must be provided on public roads, extending to 2.4m on the stock containment side and 0.6m on the other side.
Depending upon the road class, a by-pass lane for stock, abnormal loads etc. must be provided.