Highway Slope Manual

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For the control of visual impact of new slopes, the use of sprayed concrete or other hard
surface on slopes should only be considered as a last resort and only after other techniques have
been explored and found not practical. This principle should also be adopted for both
preventive maintenance and upgrading works to existing slopes.
Detailed guidance on landscape treatment and bio-engineering techniques for manmade
slopes and retaining walls is presented in GEO Publication No. 1/2000 (GEO, 2000).
6.2 PLANNING OF LANDSCAPE WORKS
For new road or road improvement projects involving slope works, it is necessary to
consider landscape, visual and ecological impact issues as part of the planning process. For
major projects, a landscape, visual and ecological impact assessment should be part of the
statutory Environmental Impact Assessment (Environmental Protection Department, 1997 and
1998). This will require the input of landscape architects at various stages of the project and
due allowance should be made for programming and funding arrangements.
The resources to be allocated to the landscape/visual design of a roadside slope should
be proportional to the visual sensitivity of the location. As a guide, the provision for
landscape works should be around 10% but could be up to 20% of the cost estimate for the
slope works for very sensitive locations.
6.3 DESIGN CONSIDERATIONS
6.3.1 General
In planning new highway and road improvement projects, areas of high aesthetic value
should be avoided and, where unavoidable, every effort must be made to minimise the overall
impact and to preserve the balance of every aspect of the environment. Existing landscape
features, e.g. trees and rock outcrops, should be retained where possible.
It is important that the engineering and landscape solutions are not developed in
isolation from each other, but as part of an integrated process. The aesthetic design solution
of a slope should take account of the specific local environmental characteristics and setting
(e.g. colouring, micro-climate and vegetation types). Even if two slopes at different
locations have similar geotechnical characteristics, the aesthetic considerations may be quite
different. For example, attention should be given to the colours in the surrounding landscape
as well as textures of vegetation and rock which might be complemented in the final design
(Department of Transport, 1992).
Slopes in urban or urban fringe areas demand solutions that are different from those
appropriate to rural, rural fringe or Country Park areas. Consideration should be given to
adopting solutions that provide opportunity to enhance the environment with vegetation.
Where vegetation is to be established on a slope, the planting design should as far as
practicable seek to promote the development of ecologically balanced plant communities,
preferably using native species in the area, with a view to supporting wildlife as well as to