The landscape is the viewed external environment and includes such elements as terrain (Section 6.1.3), water, flora, fauna, farms, towns, and roads. Landscape issues enter into the planning of a road (Chapters 5 and 31), the assessment of its environmental consequences (Chapter 32), alignment design (Section 6.2), construction (Chapter 25), maintenance (Chapter 26), and operations (Chapter 18). In considering landscaping issues, it is necessary to take into account its influence on:
* the road users (it is important to realise that the road user will be viewing the landscape whilst in motion),
* the occupants of the surrounding land,
* the intrinsic natural, social, cultural, and historic characteristics of the area, and * items in the existing landscape which are unique and/or of high visual value. The landscape resulting from road construction must therefore satisfy the following five objectives of helping the road to:
(a) fit harmoniously into the external visual environment, creating an interesting and pleasing scene for both travellers and non-road users, e.g. by linking components of the landscape and screening unsightly views,
(b) function sensitively within the processes that occur in the external environment, (e.g. by preserving local movement systems and by conserving existing topsoil, controlling water run-off, and preventing soil erosion, Section 13.3.1),
(c) perform its intended traffic function by: – leading the driver’s eye,
– signaling changes in alignment, – delineating the alignment,
– screening the glare from oncoming headlights (Section 24.4.2),
– providing forgiving traffic barriers to minimise damage to errant vehicles (Section 28.6.2),
– reducing side winds,
– relieving driver boredom, and
– providing a reference point for speed indication.
(d) improve travel amenity by providing areas for rest and shelter, and
(e) respect local environmental, cultural, and conservation values (e.g. by preserving remnant vegetation).
Usually, the road builder can only influence the landscape in the verge beside the road, although the planners may have had an opportunity to locate the road within the overall landscape. Landscaping also covers such construction and maintenance matters as:
(1) site clearing, and methods of retaining as much as possible of the existing ground cover,
(2) disposing of unwanted, existing soil and vegetation and removing construction debris,
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(4) reducing maintenance costs by selecting plantings requiring low maintenance and controlling soil erosion, rockslides, and snow slides.
(5) selecting the plant stock, seeds, and fertiliser to be used, (6) planning future plant maintenance,
(7) providing for the movement of local wildlife, and
(8) selecting the best way of utilising small parcels of land left over from land resumption activities (Section 6.3).
Useful guidance on road ecology is given in Forman et al. (2003).
6.4.2 Design
It will usually be found that the longitudinal vertical alignment will have greater visual impact on motorists than the horizontal alignment or cross-section, particularly when cuttings and embankments are involved. However, long straight sections, monotonous horizontal alignments, and isolated sharp curves can have a major influence on driver behaviour (Sections 16.5.2 and 18.2.1).
Cost conflicts will often arise. For example, flat rather than steep slopes on the sides and faces of cuttings and embankments will usually prove better at blending into the landscape and supporting vegetation. However, they will be more expensive than steep slopes. The correct balance between the two is not easy to achieve, as it is difficult to put a value on aesthetics.
Consideration should be given to wayside stops, rest areas, truck-parking areas, and scenic lookouts. Information bays or off-road facilities on the approaches to large towns and tourist facilities can be useful. Wayside stops are commonly provided at 50 km intervals, reducing to 20 km when AADT exceeds 2500 or to 10 km when tourist activity is high. Rest (or service) areas that additionally provide water, toilet and shelter, are recommended when AADTs exceed 1000 and comparable town facilities are more than 50 km apart. Drivers prefer rest areas that are large and shady (Pearce and Promnitz, 1982). From an engineering viewpoint, the sites should be at road level with good entry and exit sight distances and adequate drainage. Ideally, they should be able to be developed within the strip of land already reserved for the road.
Roads can be a barrier to the movement of many animal species. Where this will be a threat to the local species, movement can be catered for by well-placed overpasses, tunnels, culverts and pipes. The solution adopted must be tailored to suit the specific species under threat (Maningian, 1996).
6.4.3 Plantings
It is usually desirable to begin selecting the landscape planting by conducting a survey of the pre-existing flora and fauna (Section 6.1.1), as part of an assessment of the whole environmental framework of the area (Section 32.1.1). This can vary from comprehensive catalogues, to data on significant single specimens, to surveys of complex ecological areas. The stability, interdependency, sensitivity, vulnerability, and resistance to change of each type needs to be understood. Plantings (and future maintenance) should encourage the development over time of natural plant communities. Specific reference should be made to protected plants, pest plants, and historic plants. Possible surgery or maintenance
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of existing vegetation also needs consideration. Local seedstock can be collected for planting after construction is finished.
Natural features that require evaluation include environmentally-sensitive areas such as an unusual stand of trees or a creek line, the character of the landscape, and the existing land usage. Other desirable data relate to the quality, quantity and permanence of surface and subterranean water. Photographic records are useful. It is important to delineate those features that should be preserved. For example, stands of trees can be included in the road reservation and utilised as a roadside amenity or used as part of the overall planting pattern.
Construction often leaves the land in a highly disturbed state that may initially be unable to support plantings of the final mature species. Thus some patience and staged planting may need to be employed. For instance, many maturing plants favourably alter local site conditions and permit a ‘succession’ of plant species to take hold until, finally, a mature self-regenerating set of species arises. The resulting strata of grass, shrubs, and trees will often also provide a well-used animal habitat.
Shrubs can serve most of the same purposes as trees and also reduce mown areas. Evergreen shrubs with a dense, compact habit and growing up to 2 m high are particularly effective as anti-dazzle screens. To be safe as traffic barriers, shrubs should have resilient stems rather than single trunks of over 100 mm in diameter.
In planting trees, it is necessary to minimise collisions by cars (Section 28.6.1) and the effect of falling branches. The former factor usually controls tree placement and the common recommended 9 to 10 m clearance from traffic is often reduced to 2 m for shrubs. Trees are rarely planted on steep slopes, or where they would obstruct drains or reduce sight distance. Tree planting issues are discussed further in Section 7.4.2. Not every area needs to be intensively planted, and the roadside verge can also contain wildflower patches, sandy and rocky areas and wetlands.
Slope protection on embankments and cuttings (Section 11.8.2) is an important part of landscaping works. If preventative measures are not taken, such areas can be readily scoured by surface water flows (Section 13.3.1). The two keys are good surface cover and adequate drainage to prevent surface flows. Surface cover may be provided by a man- made cover (e.g. stones or concrete) or by planting. Plant growth may be made difficult because the construction process will usually leave the slope devoid of topsoil. Thus material may need to be imported and then held in place until leaf and root growth are adequate. This can be done by using soil sods containing young grass or by stabilising the slope with bitumen sprays, mulch mixtures, netting, brush, mesh, or various combinations of these.