The 2009 IRC SP 21 offers detailed guidance on landscaping and tree planting tailored for Indian highways, covering species choice, plantation layouts, upkeep, and environmental factors. It supports highway engineers, planners, and landscape designers in incorporating vegetation within road infrastructure to boost visual appeal, safety, and ecological harmony across varied Indian climates and soils.
Overview
The 2009 IRC SP 21 offers detailed guidance on landscaping and tree planting tailored for Indian highways, covering species choice, plantation layouts, upkeep, and environmental factors. It supports highway engineers, planners, and landscape designers in incorporating vegetation within road infrastructure to boost visual appeal, safety, and ecological harmony across varied Indian climates and soils.
Audience
Contents
Structure
This section outlines the coverage of landscaping and roadside plantation measures for highways, emphasizing safety, aesthetics, and environmental benefits applicable to both rural and urban roads. It includes landscaping for highway structures and slope protection, along with maintenance and enhancement of existing roadside greenery. Detailed planting densities for new multi-lane rural highways and typical cross-sectional layouts are provided, referencing appendices for species selection and slope treatment.
Key considerations include topography, environmental preservation, climatic conditions, and operational safety. Roads should align with natural terrain to minimize earthwork and retain scenic value. Vegetation and habitats must be protected, with species chosen based on local climate. Landscaping must not compromise visibility or safety, advocating gradual thinning and selective pruning to create pleasing views and screen undesirable sights.
Specifications for subgrade preparation and typical cross-sectional dimensions for new rural highways are detailed. Plantation densities per kilometer and landscape integration with geometric design principles are emphasized. Native species and appropriate spacing are recommended to ensure growth, visibility, and slope protection.
Borrow areas should comply with IRC standards and be positioned to minimize visual impact. Slope shaping with flattened and rounded cut faces, proper drainage to prevent waterlogging, and conversion of large borrow pits into water features or landscaped zones are advised.
Recommendations address acquiring sufficient land width to accommodate stable slopes, medians, plantations, and scenic areas. Urban road ROW considerations include zoning, traffic volume, provision for footpaths, cycle tracks, utilities, environmental buffers, and cost implications.
Guidelines cover subgrade preparation beneath approaches, shoulder dimensions, and typical cross-section layering. Tree planting densities, spacing, and protective tree guard measures are outlined to ensure healthy growth and roadside safety.
Designs specify locations near checkpoints and border areas with ample shaded parking using hardy trees and shrubs. Green spaces integrate paving and grassing to reduce upkeep, with screen planting used to buffer noise and dust.
Use of water-tolerant and salt-resistant species is outlined, alongside soil preparation techniques like raised beds and mulching. Vegetation stabilizes embankments and reduces erosion, with plant spacing formulas provided.
A gradual thinning method combined with simultaneous new planting maintains greenery while preparing for road construction. Selective pruning exposes scenic views and screens undesirable sights, preserving environmental and aesthetic values.
Ensuring minimum survival rates, appropriate spacing, and sapling height are essential to maintain sight distances and driver safety. Low-height ornamental plants near carriageways and taller trees farther out optimize visibility.
Species are recommended according to soil and climatic conditions. Pit preparation and spacing guidelines support healthy establishment, with adaptations for alkaline and waterlogged soils.
Pruning promotes healthy growth and safety, with specific seasons for major trimming. Maintenance includes fencing, replacing dead plants, weed control, and watering, ensuring plantation vitality and roadside safety.
Planting operations are aligned with monsoon onset for optimal growth. Detailed activity schedules spanning multiple years include site preparation, planting, watering frequencies, and casualty replacements.
Planting is prohibited within clearance zones adjacent to carriageways to prevent root damage and ensure safety. Spacing, pit size, and survival rates are specified for plantations beyond these zones.
Lists of suitable tree species for arid, temperate, and Indo-Gangetic plain regions are provided. Guidelines address no plantation zones, visibility clearances on curves, and species selection for medians and screening.
Frequently Asked
IRC SP 21 recommends specific tree species tailored to soil types and climate zones. For normal loamy soils, species like Acacia auriculiformis, Bauhinia, Cassia, Delonix regia, and Peltophorum are suitable. Waterlogged areas favor Cordia dicotoma and Terminalia arjuna, while alkaline soils call for Albizzia lebbek and Pongamia pinnata. Subsequent rows include species such as Dalbergia sissoo and Grevillea robusta. Shade trees like Terminalia arjuna and Mangifera indica are recommended in last rows.
Plantations should maintain adequate spacing—shade trees spaced 8 to 12 meters apart—to avoid dense growth that impairs visibility. No planting should occur near curves to preserve a stopping sight distance of 170 meters for 100 km/h design speed. Trees must be offset at least 1 meter beyond the roadway edge, with smaller ornamental trees closer to the road and taller shade trees positioned further away to balance safety and aesthetics.
For waterlogged zones, species tolerant of saturated soils are advised, along with raised beds to improve drainage and prevent root suffocation. In saline or coastal areas, salt-resistant plants like Casuarina and Prosopis are recommended, combined with windbreaks and soil amendments. Native species adapted to local conditions should be used to enhance stability and ecological balance.
Regular pruning removes weak, diseased, or obstructive branches to promote healthy growth and maintain safety. Protective fencing must be maintained, and dead or damaged plants replaced before monsoons. Weed control and removal of dry leaves reduce fire hazards. Dedicated horticulture supervision ensures timely care and adherence to maintenance schedules.
Adequate right-of-way should be acquired to accommodate plantations, scenic spots, and ecological buffers. Landscaping must be integrated into project designs and cost estimates. Roads should be aligned to maximize scenic views while using selective tree groups to screen undesirable sights. Gradual thinning of existing forests combined with simultaneous new planting preserves greenery and minimizes environmental impact.
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