9. Transportation (ACiE09)

9.1 Highway Planning and Survey

Highway planning and survey form the foundational steps in developing efficient and safe road networks. It involves understanding various modes of transport, historical context, road classifications, and meticulous surveying techniques.

Modes of Transport

Transportation systems facilitate the movement of people and goods. The primary modes include:

• Road Transport: Flexible, door-to-door service, suitable for short to medium distances.
• Rail Transport: Efficient for bulk goods and long-distance passenger travel, high capacity.
• Air Transport: Fastest for long distances, high cost, suitable for perishable goods and urgent travel.
• Water Transport: Cheapest for bulk goods, slow, limited by waterways.
• Pipeline Transport: Specialized for liquids and gases, continuous flow, low operating cost.

History of Road Development in Nepal

Nepal's road development has seen significant strides, particularly with major projects:

• East-West Highway (Mahendra Highway): A backbone of Nepal's road network, connecting the eastern and western regions, crucial for economic integration and accessibility.
• Ring Roads: Kathmandu Ring Road is a prime example, alleviating urban congestion and improving intra-city connectivity. Similar concepts are being developed in other major cities.

Classification of Roads (as per Nepal Road Standards)

Roads in Nepal are classified based on their administrative function and traffic volume, primarily aligning with DOR guidelines:

• National Highways (NH): Main arterial roads connecting major cities, provincial capitals, and international borders. High design standards.
• Strategic Roads (SR) / Provincial Highways (PH): Connect district headquarters, important towns, and link to National Highways.
• District Roads (DR): Connect rural areas to district headquarters and market centers.
• Urban Roads: Roads within municipal areas, designed for urban traffic characteristics, including local streets, collector roads, and arterial roads.

Road Survey

A systematic process to gather data for road design:

1. Reconnaissance Survey: Initial investigation to identify feasible routes, considering topography, existing features, and potential obstacles.
2. Preliminary Survey: Detailed survey of selected routes, involving topographic mapping, soil investigation, and hydrological studies.
3. Final Location Survey: Precise staking out of the chosen alignment on the ground, establishing control points, and collecting final design data.

Highway Alignment and Controlling Factors

Highway alignment refers to the three-dimensional path of the road. Key controlling factors include:

• Gradient: Longitudinal slope of the road. Steeper gradients increase vehicle operating costs and reduce safety.
• Curvature: Horizontal bends in the road. Sharp curves reduce speed and visibility.
• Terrain: Flat, rolling, mountainous terrain dictates the complexity and cost of construction.
• Geology: Soil type, rock formations, and stability influence earthwork and foundation design.
• Economy: Construction, maintenance, and user costs are critical in selecting an alignment.
• Environmental Factors: Impact on ecosystems, cultural sites, and human settlements.

Evaluating Alternate Alignments

Multiple feasible alignments are typically identified and evaluated based on:

• Cost-Benefit Analysis: Comparing initial construction costs, maintenance costs, and user benefits (travel time savings, reduced accidents).
• Environmental Impact Assessment (EIA): Analyzing potential impacts on air, water, soil, flora, fauna, and human communities, and proposing mitigation measures.

Road Standards of Nepal

Road design and construction in Nepal primarily follow:

• Indian Road Congress (IRC) Guidelines: Many IRC codes are adopted or adapted due to similar geographical and traffic conditions.
• Department of Roads (DOR) Guidelines: Specific manuals and standards developed by the Department of Roads, Government of Nepal, tailored to local conditions and requirements.

9.2 Geometric Design of Highway

Geometric design deals with the physical dimensions and layout of the highway, ensuring safety, efficiency, and comfort for drivers.

Basic Design Control and Criteria

• Design Speed: The maximum safe speed at which a vehicle can travel on a given section of road under favorable conditions. It dictates curve radii, sight distances, and gradients.
• Traffic Volume: The number of vehicles using the road, influencing the number of lanes, intersection design, and capacity.
• Terrain: Flat, rolling, or mountainous terrain affects the feasibility and cost of geometric elements.

Elements of Highway Cross-Section

The cross-section defines the various components perpendicular to the road's centerline:

• Carriageway Width: The part of the road used by vehicular traffic. Width depends on the number of lanes and design vehicle.
• Shoulders: Adjacent to the carriageway, providing lateral support, emergency stopping space, and space for disabled vehicles.
• Medians: Separating opposing traffic streams, enhancing safety and aesthetics.
• Side Drains: Channels along the road to collect and divert surface runoff.
• Embankment: Raised section of the road above natural ground level.
• Cutting: Section of the road below natural ground level.

Highway Curves

Horizontal Curve

Used to change the direction of the highway. Key elements:

• Transition Curve: Gradually introduces super-elevation and curvature, improving driver comfort and safety.
• Super-elevation (e): The transverse slope provided to counteract centrifugal force on horizontal curves. e + f = V² / (127R) Where:
  • e = rate of super-elevation (m/m or ft/ft)
  • f = coefficient of lateral friction
  • V = design speed (km/h or mph)
  • R = radius of the horizontal curve (m or ft)
  For design, friction is often ignored for full super-elevation calculation: e = V² / (127R)
• Minimum Radius (Rmin): The smallest radius allowed for a given design speed and maximum super-elevation/friction. Rmin = V² / (127 * (e_max + f_max))
• Adverse Camber: Occurs when the outer edge of a curve is lower than the inner edge, or the normal camber is not fully removed, creating an unsafe condition.

Gradients

• Average Gradient: The overall slope of a road section.
• Ruling Gradient: The maximum gradient that should be adopted under normal circumstances.
  • Flat terrain: 1 in 30 (3.3%)
  • Rolling terrain: 1 in 20 (5%)
  • Mountainous terrain: 1 in 17 (5.88%)
  • Steep terrain: 1 in 14 (7.14%)
• Limiting Gradient: Steeper than ruling gradient, used only when ruling gradient is unavoidable.
• Exceptional Gradient: Used for short stretches under extreme conditions.

Sight Distance

• Stopping Sight Distance (SSD): The minimum distance required for a driver to stop a vehicle safely to avoid collision. SSD = vt + V² / (254 * (f ± G)) (for V in km/h) or SSD = vt + v² / (2g * (f ± G)) (for v in m/s) Where:
  • v = design speed (m/s) or V = design speed (km/h)
  • t = reaction time (usually 2.5 seconds for SSD)
  • g = acceleration due to gravity (9.81 m/s²)
  • f = coefficient of longitudinal friction
  • G = gradient (decimal, + for upgrade, - for downgrade)
• Passing Sight Distance (PSD): The minimum distance required for a driver to safely overtake another vehicle. More complex calculation involving multiple vehicle movements.

Design Considerations for Horizontal Alignment

• Minimum Radius: Determined by design speed, max super-elevation, and friction.
• Transition Length: Length required to achieve full super-elevation and gradually introduce curvature. Calculated based on rate of change of super-elevation and centrifugal acceleration.

Design Considerations for Vertical Alignment

Vertical curves connect different gradients.

• Crest Vertical Curve: Convex curve, critical for sight distance. Length determined by K-value (rate of change of grade per 1% change) for SSD or PSD. L = K * A (where A is algebraic difference in grades)
• Sag Vertical Curve: Concave curve, critical for headlight sight distance and comfort. Length determined by K-value for headlight sight distance or comfort.

Extra Widening

Provided on horizontal curves to account for off-tracking of vehicles and psychological effects.

We = (nL² / (2R)) + (V / (9.5√R)) Where:

• We = extra widening (m)
• n = number of lanes
• L = length of wheel base (m)
• R = radius of curve (m)
• V = design speed (km/h)

Set Back Distance from Center of Inner Lane

Minimum distance from the center of the inner lane to an obstruction on a horizontal curve to ensure adequate sight distance.

Design of Road Drainage Structures

• Cross Drains: Culverts or bridges to carry water across the road (e.g., streams, rivers).
• Side Drains: Open channels or covered pipes along the sides of the road to collect surface runoff.
• Camber (Cross Slope): Transverse slope provided to the carriageway surface to drain rainwater quickly. Typically 2-3% for asphalt, 3-4% for gravel roads.

Design Considerations for Hill Roads

• Hairpin Bends: Sharp U-turns used in steep terrain to gain elevation in a limited space. Require careful design for safety.
• Retaining Walls: Structures built to hold back soil and prevent landslides on steep slopes.
• Slope Protection: Techniques like terracing, bio-engineering, gabion walls, and shotcrete to stabilize cut and fill slopes.

9.3 Highway Materials

The selection and testing of highway materials are crucial for the long-term performance and durability of pavements.

Types of Aggregates

• Coarse Aggregates: Retained on 4.75 mm sieve (e.g., crushed stone, gravel).
• Fine Aggregates: Passing 4.75 mm sieve (e.g., sand, stone dust).

Tests on Aggregates

• Gradation (Sieve Analysis): Determines the particle size distribution, impacting workability and void content.
• Strength:
  • Aggregate Crushing Value (ACV): Measures resistance to crushing under compressive load. Lower ACV indicates stronger aggregate.
  • Aggregate Impact Value (AIV): Measures resistance to sudden shock or impact. Lower AIV indicates tougher aggregate.
• Durability:
  • Aggregate Abrasion Value (AAV) (Los Angeles Abrasion Test): Measures resistance to wear and tear due to abrasive action. Lower AAV indicates more durable aggregate.
  • Soundness Test: Evaluates resistance to weathering actions (e.g., freeze-thaw cycles) using magnesium or sodium sulfate solutions.

Binding Materials

Bitumen (asphalt) is the most common binder for flexible pavements.

• Bitumen Grades: Classified by penetration value (e.g., 60/70, 80/100) or viscosity (e.g., VG-30, VG-40).
• Penetration Test: Measures the hardness or consistency of bitumen by the depth a standard needle penetrates in 5 seconds under a specific load and temperature.
• Viscosity Test: Measures resistance to flow, indicating the fluidity of bitumen at various temperatures.
• Softening Point Test: Temperature at which bitumen attains a certain degree of fluidity (Ring and Ball apparatus). Indicates temperature susceptibility.
• Ductility Test: Measures the ability of bitumen to stretch without breaking, indicating its cohesive and adhesive properties.
• Specific Gravity Test: Ratio of the density of bitumen to the density of water, useful for mix design calculations.

Design of Asphalt Mixes (Marshall Method)

A widely used empirical method for designing hot mix asphalt (HMA) mixtures to achieve desired performance properties.

• Stability: Resistance to plastic flow under load (measured in kN).
• Flow: Deformation of the specimen at maximum load (measured in mm).
• Voids in Total Mix (VTM): Air voids percentage in the compacted mix.
• Voids in Mineral Aggregate (VMA): Volume of voids between aggregate particles in a compacted mix, including air voids and effective bitumen content.
• Voids Filled with Bitumen (VFB): Percentage of VMA filled with bitumen.

Optimal bitumen content is selected based on a balance of these properties to meet specified criteria (e.g., as per IRC/DOR). Example: Target VTM 3-5%, VMA 14-16%, Stability > 8 kN.

Evaluation of Subgrade Soil

• California Bearing Ratio (CBR) Test: Measures the strength of the subgrade soil relative to a standard crushed stone. It's a critical input for flexible pavement design. Higher CBR indicates stronger subgrade.
• Plate Load Test: Determines the bearing capacity and settlement characteristics of the subgrade or subbase layers under actual loading conditions.

9.4 Traffic Engineering and Safety

Traffic engineering focuses on safe and efficient movement of people and goods, while road safety aims to minimize accidents and their severity.

Impact of Human and Vehicular Characteristics on Traffic Planning

• Human Factors: Driver reaction time, perception, vision, fatigue, age, and behavior influence road design and traffic control.
• Vehicular Factors: Vehicle dimensions, weight, speed capabilities, braking characteristics, and acceleration affect lane width, curve design, and signal timing.

Traffic Operations and Regulations

Involve managing traffic flow, enforcing rules, and optimizing network performance through measures like speed limits, parking restrictions, and one-way systems.

Traffic Control Devices

• Signs: Regulatory (e.g., stop, yield), Warning (e.g., curve ahead), Guide (e.g., destination, route numbers).
• Markings: Pavement lines (e.g., center lines, lane lines, crosswalks), words, and symbols.
• Signals: Traffic lights (red, yellow, green), pedestrian signals.
• Islands: Raised areas within the roadway to guide traffic, protect pedestrians, or channelize turns.

Traffic Studies

• Volume Study: Counts the number of vehicles passing a point over a period to determine Average Daily Traffic (ADT) and peak hour volume.
• Speed Study:
  • Spot Speed Study: Measures instantaneous speed at a specific location.
  • Time-Mean Speed (TMS): Average of spot speeds of all vehicles passing a point over a time interval.
  • Space-Mean Speed (SMS): Average speed of vehicles over a length of roadway at any given instant.
• Origin-Destination (O&D) Study: Determines where trips begin and end, crucial for transportation planning and forecasting.
• Traffic Capacity: Maximum flow rate a road segment can handle.
  • Basic Capacity: Theoretical maximum under ideal conditions.
  • Possible Capacity: Maximum flow under prevailing road and traffic conditions.
  • Practical Capacity: Maximum flow that allows for reasonable operating speed and driver comfort.
• Traffic Flow Characteristics: Relationship between flow, density, and speed. q = k * v Where:
  • q = traffic flow (vehicles/hour)
  • k = traffic density (vehicles/km)
  • v = space-mean speed (km/h)
• Parking Study: Analyzes parking demand, supply, and duration, informing parking facility design.
• Accident Study: Collects and analyzes accident data to identify causes, high-risk locations (black spots), and develop countermeasures.

Road Intersections

• Types of At-Grade Intersections:
  • T-Junction: Three-leg intersection.
  • Crossroad: Four-leg intersection.
  • Rotary/Roundabout: Circular intersection where traffic flows in one direction around a central island.
• Grade-Separated Intersections:
  • Flyover: One road passes over another.
  • Underpass: One road passes under another.
• Configurations and Design: Involve channelization, turning radii, sight distance, and signalization to optimize flow and safety.

Traffic Lights

• Fixed Time Signals: Pre-timed intervals for green, yellow, red phases, regardless of actual traffic demand.
• Vehicle Actuated Signals: Detect vehicle presence and adjust signal timings dynamically based on real-time demand.
• Webster's Method for Cycle Length: A common method for calculating optimal signal cycle length for fixed-time signals. Co = (1.5 * L + 5) / (1 - Y) Where:
  • Co = optimal cycle length (seconds)
  • L = total lost time per cycle (seconds)
  • Y = sum of critical flow ratios for all phases

Factors Influencing Night Visibility

Headlight glare, poor street lighting, adverse weather, and reflective properties of surfaces affect driver's ability to see at night, increasing accident risk.

Road Safety Measures

• Road Safety Audit: A systematic process of checking the safety performance of a road project during design, construction, and early operation.
• Black Spot Treatment: Identifying locations with high accident frequency ("black spots") and implementing specific engineering, enforcement, or educational measures to reduce accidents.

9.5 Road Pavement

Pavement design ensures that the road structure can withstand traffic loads and environmental factors over its design life.

Different Types of Pavement

• Flexible Pavement: Consists of multiple layers (asphalt concrete surface, granular base, subbase) resting on the compacted subgrade. Load is distributed through granular action.
  • Layers: Surface Course (wearing course), Binder Course, Base Course, Subbase Course, Subgrade.
• Rigid Pavement: Consists of a Portland Cement Concrete (PCC) slab directly on a subbase or subgrade. The slab itself provides structural strength, distributing load over a wide area.
  • Layers: PCC Slab, Subbase, Subgrade.

Design Methods for Flexible Pavement

• CBR Method (California Bearing Ratio Method): Empirical method widely used in India (IRC 37) and Nepal (DOR). It relates the subgrade CBR value, traffic volume (in standard axles), and material properties to determine required pavement layer thicknesses.
• Burmister's Layered Theory: Mechanistic-empirical approach based on elastic theory for multi-layered systems. Calculates stresses, strains, and deflections in each layer.
• DOR Guidelines: Department of Roads, Nepal, provides specific design charts and procedures adapted from IRC for flexible pavements.

Design Methods for Rigid Pavement

• PCA Method (Portland Cement Association Method): Mechanistic-empirical method considering traffic loading, subgrade support (k-value), and concrete properties to determine slab thickness and jointing.
• IRC Method (IRC 58): Based on Westergaard's stress analysis, considers critical stresses (corner, edge, interior) due to wheel loads and temperature variations.

Loads and Other Factors Controlling Pavement Design

• Traffic Loading: Primarily expressed as Equivalent Single Axle Load (ESAL) repetitions. Heavier loads and higher repetitions require stronger pavements.
• Environmental Factors: Temperature variations (thermal expansion/contraction), moisture content (subgrade swelling/shrinkage, frost heave), and precipitation affect pavement performance and durability.

Stress due to Load (Westergaard Stress Analysis)

For rigid pavements, critical stresses occur at specific locations:

• Westergaard Corner Stress: Maximum stress at the corner of a slab, critical when a wheel load is applied near the corner.
• Westergaard Edge Stress: Maximum stress along the edge of a slab, critical when a wheel load is applied near the edge.

Stress due to Temperature

• Thermal Curling: Differential temperature across the slab depth causes the slab to curl upwards (when top is cooler) or downwards (when top is warmer), inducing stresses.
• Warping Stress: Stresses induced by temperature gradients across the depth of the concrete slab.

9.6 Road Construction and Maintenance

Effective construction and timely maintenance are vital for the longevity and serviceability of roads.

Activities, Techniques, Tools, Equipment and Plants Used in Road Construction

• Earthwork: Excavation (excavators, dozers), filling, compaction (rollers).
• Aggregate Production: Crushers, screeners.
• Mixing Plants: Asphalt mixing plants (hot mix plants), concrete batching plants.
• Laying Equipment: Pavers (for asphalt and concrete), motor graders.
• Compaction Equipment: Smooth wheel rollers, pneumatic tire rollers, vibratory rollers.
• Haulage: Dumpers, trucks.

Preparation of Road Subgrade

• Clearing and Grubbing: Removing vegetation, trees, and roots from the right-of-way.
• Compaction: Achieving specified density and moisture content using rollers to ensure adequate strength and stability.
• Testing: Field density tests (e.g., sand replacement, nuclear density gauge) to verify compaction.

Field Compaction Control

• Nuclear Density Gauge: Rapid, non-destructive method to measure in-situ density and moisture content.
• Sand Replacement Test: Measures the volume of a excavated hole, which is then filled with sand of known density to determine the in-situ density.

Soil Stabilization

Improving the engineering properties of soil to enhance strength, reduce plasticity, and improve durability.

• Lime Stabilization: Used for clayey soils to reduce plasticity, improve workability, and increase strength.
• Cement Stabilization: Forms a rigid or semi-rigid layer, increasing strength and stiffness, suitable for various soil types.
• Bitumen Stabilization: Binds soil particles, reducing permeability and improving cohesion, often used for granular soils.
• Geosynthetics: Geotextiles, geogrids, geomembranes used for reinforcement, separation, filtration, and drainage.

Construction of Asphalt Concrete Layers

• Mixing: Aggregates and bitumen are heated and mixed in an asphalt plant at specific temperatures (e.g., 150-170°C for aggregates, 140-160°C for bitumen).
• Laying: Hot mix asphalt is transported to the site and spread uniformly by pavers.
• Compaction Temperatures: Compaction must occur within a specific temperature range (e.g., breakdown rolling 130-140°C, intermediate rolling 100-120°C, finish rolling > 80°C) to achieve desired density and void content.

Construction Procedure for Other Pavements

• Penetration Macadam: Layers of coarse aggregate are spread, compacted, and then sprayed with hot bitumen, followed by spreading and rolling of key aggregates.
• Bituminous Bound Macadam (BBM): Similar to penetration macadam but with finer aggregates and often a thicker bitumen application.
• Plain Cement Concrete (PCC) Pavements:
  • Jointing: Contraction joints (to control cracking from shrinkage), expansion joints (to accommodate thermal expansion), and construction joints (at end of day's work) are crucial.
  • Curing: Maintaining moisture content and temperature to ensure proper hydration of cement and strength gain (e.g., ponding, wet hessian, curing compounds).

Road Maintenance

• Routine Maintenance: Regular, minor works (e.g., pothole patching, drain cleaning, shoulder repair) to keep roads in good condition.
• Periodic Maintenance: Major works performed at intervals (e.g., resurfacing, overlay, seal coats) to restore structural integrity and riding quality.
• Emergency Maintenance: Urgent repairs for unexpected damage (e.g., landslide clearance, flood damage repair).

Repair and Rehabilitation

• Overlay: Adding new layers of asphalt or concrete to an existing pavement to improve structural capacity and rideability.
• Cold Recycling: Reusing existing pavement materials by mixing them with new binder (emulsion or foam bitumen) and/or rejuvenators at ambient temperatures.
• Crack Sealing: Filling cracks in the pavement surface with suitable sealants to prevent water ingress and further deterioration.