Transportation Engineering- II (CE-502) - Unit 2 Short Notes

UNIT 2: TRANSPORTATION ENGINEERING-II (CE-502)

Exam-Focused Short Notes Based on RGPV Past Papers (JUN 2025, MAY 2024, NOV 2023)

I. HIGHWAY GEOMETRIC DESIGN & ALIGNMENT

1.1 Horizontal Curves

• Purpose: Provide smooth transition between straight sections, change direction safely, and improve aesthetics.

• Types:

  • Simple Circular Curve: Single constant radius; most common.

  • Compound Curve: Two or more circular curves with different radii on same side.

  • Reverse Curve: Two circular curves in opposite directions; requires transition curve.

  • Transition (Spiral) Curve: Radius varies gradually; used for high-speed roads to introduce centrifugal force slowly.

• Geometric Elements (for simple circular curve):

  • Radius (R): Constant radius of curve.

  • Deflection Angle (Δ): Angle between tangents.

  • Tangent Length (T): $$\displaystyle T = R \tan\left(\frac{\Delta}{2}\right) $$

  • Length of Curve (L): $$\displaystyle L = \frac{\pi R \Delta}{180} $$ (in degrees)

  • Chord (C): $$\displaystyle C = 2R \sin\left(\frac{\Delta}{2}\right) $$

  • External Distance (E): $$\displaystyle E = R \left( \sec\frac{\Delta}{2} - 1 \right) $$

  • Mid-ordinate (M): $$\displaystyle M = R \left(1 - \cos\frac{\Delta}{2}\right) $$

[!TIP]

For transition curves, length is designed based on rate of change of centrifugal acceleration (usually 0.5 m/s³ as per IRC).

1.2 Superelevation (Banking)

• Concept: Outer edge of carriageway raised to counteract centrifugal force, improve safety and comfort.

• Derivation:

  From equilibrium:

$$e + f = \frac{V^2}{gR}$$

where $e$ = superelevation (ratio), $f$ = side friction factor, $V$ = speed (m/s), $g$ = 9.81 m/s², $R$ = radius (m).

In practical units ($V$ in kmph, $R$ in m):

$$e + f = \frac{V^2}{127R}$$

• Design of Rate of Superelevation:

  1. Determine maximum $f$ from IRC tables for given speed.

  2. Compute $$\displaystyle e = \frac{V^2}{127R} - f $$.

  3. Check against max/min limits.

• IRC Limits:

  • Maximum: 7% (plain/rolling terrain), 10% (hilly terrain).

  • Minimum: -2% (for drainage in plain areas).

• Balanced Superelevation: When $e$ is designed for maximum $f$ at design speed.

• Unbalanced Superelevation: When $e$ is less than balanced value; relies on friction for higher speeds.

[!TIP]

For mixed traffic (slow/fast vehicles), design for maximum superelevation to avoid overturning risk for slow vehicles.

1.3 Overtaking & Sight Distance

Overtaking Sight Distance (OSD)

• Definition: Minimum distance required for a driver to overtake a slower vehicle safely.

• Factors: Speeds of overtaking ($$\displaystyle V_b $$) and overtaken ($$\displaystyle V_t $$) vehicles, acceleration, reaction time, vehicle lengths, safety margin.

• Derivation (Two-Lane Highway):

$$OSD = (V_t + V_b)(t + T) + (L + s)$$

where:

• $$\displaystyle V_t $$, $$\displaystyle V_b $$ in m/s (or use $$\displaystyle 0.278(V_t+V_b) $$ if in kmph),

• $t$ = reaction time (2 sec),

• $T$ = overtaking time = $$\displaystyle \sqrt{\frac{2(L+s)}{a}} $$,

• $L$ = length of overtaken vehicle (6 m),

• $s$ = safety margin (6 m),

• $a$ = acceleration of overtaking vehicle (0.5–1.4 m/s²; typically 0.5 m/s² for cars).

• Numerical Example (JUN 2025):

  $$\displaystyle V_b = 70 $$ kmph, $$\displaystyle V_t = 40 $$ kmph.

  $$\displaystyle V_t+V_b = 110 $$ kmph = $$\displaystyle 110 \times 0.278 = 30.58 $$ m/s.

  $$\displaystyle T = \sqrt{\frac{2 \times 12}{0.5}} = 6.93 $$ sec.

  $$\displaystyle OSD = 30.58 \times (2 + 6.93) + 12 = 30.58 \times 8.93 + 12 = 273.2 + 12 = 285.2 $$ m.

Overtaking Zone

• Concept: Continuous length of road where overtaking is permitted.

• Length:

  • Minimum: Equal to OSD.

  • Desirable: $2 \times OSD$ to $3 \times OSD$ (provides multiple overtaking opportunities).

• Design: Marked with signs at start and end; should be on straight, level sections with good visibility.

[!TIP]

OSD > SSD for same speed. Always check: OSD must be greater than Stopping Sight Distance to allow safe overtaking.

Sight Distance Types

1.4 Vertical Curves

• Types:

  • Summit Curve (Convex): Crest vertical curve; design for SSD and comfort (headlight sight distance).

  • Valley/Sag Curve (Concave): Dip vertical curve; design for comfort (centrifugal force) and SSD (headlight).

• Geometric Elements: Algebraic difference in grades ($$\displaystyle N = |g_2 - g_1| $$), length of curve ($L$), tangent elevations.

• Length Design:

  • Summit Curve for SSD:

    • If $L \geq SSD$: $$\displaystyle L = \frac{N \times SSD^2}{2\sqrt{h_1} + \sqrt{h_2}} $$

      ($$\displaystyle h_1 $$ = driver’s eye height ≈ 1.2 m, $$\displaystyle h_2 $$ = object height ≈ 0.15 m)

    • If $$\displaystyle L < SSD $$: $$\displaystyle L = 2 \times SSD - \frac{2\sqrt{h_1} + \sqrt{h_2}}{N} $$

  • Valley Curve for Comfort (CSS):

$$L = \frac{A \times V^3}{127(C \pm g_1 \pm g_2)}$$

where $A$ = algebraic difference in grades, $V$ in kmph, $C$ = allowable rate of change of centrifugal acceleration (0.3 m/s³), $$\displaystyle g_1,g_2 $$ = grades.

[!TIP]

For summit curves, SSD is critical; for valley curves, comfort (CSS) controls. Always check both criteria.

1.5 Road Alignment & Engineering Surveys

• Objectives of Alignment:

  • Shortest, safest, economical, and environmentally sustainable route.

  • Smooth gradient and curvature, good drainage, minimal land acquisition.

• Map Study (Preliminary Location):

  • Uses topographical maps to identify possible routes.

  • Considers drainage, geology, existing infrastructure, political boundaries.

• Engineering Surveys (Final Location):

  1. Reconnaissance Survey: Ground inspection, preliminary data.

  2. Preliminary Survey: Detailed topographic survey, soil investigation.

  3. Detailed Survey: Final alignment, cross-sections, structure locations.

• Factors Affecting Alignment Selection:

  • Road class, topography, drainage, soil, environmental constraints, utilities, cost, safety.

[!TIP]

Alignment selection is iterative; use GIS and remote sensing for modern projects to minimize environmental impact.

II. PAVEMENT DESIGN & MATERIALS

2.1 Flexible Pavement Design (CBR Method)

• California Bearing Ratio (CBR):

  • Ratio of load at 2.5 mm or 5 mm penetration to standard load (1370 kg for 2.5 mm, 2050 kg for 5 mm).

  • Expressed as percentage; indicates soil strength.

• Design Procedure (IRC):

  1. Determine CBR of subgrade soil (soaked condition for worst case).

  2. Estimate traffic volume in terms of cumulative number of standard axles (ESA).

  3. Use IRC:37-2018 charts to find total pavement thickness for given CBR and traffic.

  4. Distribute thickness among layers (sub-base, base, surfacing) based on layer coefficients and material quality.

• Sketch:

  
  [Surface Course] (BC/WBM)
  
  [Base Course] (WMM/BM)
  
  [Sub-base Course] (Gravel/Soil-aggregate)
  
  [Subgrade] (Natural soil)
  
  

  Thickness decreases from bottom to top as material quality improves.

[!TIP]

CBR test must be performed on soaked sample for flexible pavement design to simulate worst-case moisture condition.

2.2 Rigid Pavement Design (IRC:58-2002)

• Outline:

  • Based on Westergaard’s theory for stress analysis.

  • Design Parameters:

    • Traffic classification (based on cumulative ESA).

    • Flexural strength of concrete (modulus of rupture).

    • Modulus of elasticity of concrete ($$\displaystyle E_c $$).

    • Poisson’s ratio ($\mu$ ≈ 0.15 for concrete).

    • Modulus of subgrade reaction ($k$).

  • Slab Thickness Computation:

    • Check stresses at corner, edge, and interior due to wheel load and temperature.

    • Ensure flexural stress ≤ allowable flexural strength.

    • Iterate thickness until all criteria satisfied.

  • Joint Design: Expansion, contraction, construction, longitudinal joints.

[!TIP]

IRC:58 uses single-wheel load equivalent to dual-wheel load for stress calculation. Remember to convert dual-wheel to single-wheel load using load distribution.

2.3 Comparison of Pavement Types

[!TIP]

Rigid pavement is preferred for heavy traffic and poor subgrade due to high modulus of elasticity.

2.4 Bituminous Materials & Constructions

Water Bound Macadam (WBM)

• Materials: Coarse aggregates (hard, durable), fine aggregates (stone dust), water.

• Construction:

  1. Preparation: Subgrade compacted.

  2. Laying: Aggregates spread in layers, rolled.

  3. Dry Rolling: Initial compaction.

  4. Wet Rolling: Water applied, rolled to interlock aggregates.

  5. Curing: 24 hours.

• Uses: Base course for flexible pavements, WBM roads for low traffic.

• Limitations: Not for heavy rain, requires skilled labor, maintenance prone.

Bituminous Macadam (BM) / Wet Mix Macadam (WMM)

• BM: Dense graded aggregate with bitumen binder; used as base/binder course.

• WMM: Similar to WBM but with controlled aggregate gradation and no bitumen; used as base course.

• Construction: Mixing, laying, compaction with roller.

Bituminous Concrete (BC)

• IRC Specs:

  • Materials: Coarse aggregate, fine aggregate, filler, bitumen (VG-30 or VG-40).

  • Gradation: Dense graded (gap < 5%).

  • Construction: Hot-mix plant, laying at 120–150°C, compaction with steel-wheel roller.

  • Thickness: 40–60 mm for wearing course.

• Maintenance: Overlay for distress.

Seal Coat & Tack Coat

• Tack Coat: Thin bitumen film (0.2–0.5 l/m²) sprayed between layers for adhesion.

• Seal Coat: Single layer of bitumen and sand (1.5–2 l/m²) for waterproofing and skid resistance.

[!TIP]

WBM is dry bound (no bitumen), BM/WMM may or may not have bitumen, BC has bitumen and is dense graded.

2.5 Soil Stabilization

• Mechanical Stabilization:

  • Method: Changing gradation by adding coarse/fine aggregates, densification by compaction.

  • Purpose: Improve strength, reduce swelling, enhance drainage.

  • Suitable Soils: Granular, sandy soils.

• Chemical Stabilization:

  • Lime Stabilization: For clayey soils; reduces plasticity, increases strength.

  • Cement Stabilization: For granular/silty soils; increases bearing capacity.

  • Bitumen Stabilization: For waterproofing and binding.

• Scope: Low-volume roads, base/subbase layers, rapid construction.

[!TIP]

Soil stabilization reduces construction cost by using local materials and minimizing layer thickness.

2.6 Low-Cost Roads

• Definition: Roads constructed with locally available materials at minimal cost, suitable for low traffic.

• Types:

  | Type | Materials | Construction Features | Applicability | |------|-----------|----------------------|---------------| | Earth Roads | Natural soil | Compaction, drainage | Very low traffic, rural | | Gravel Roads | Gravel aggregates | Spreading, compaction | Low traffic, seasonal | | Soil-Cement Roads | Soil + cement (3–5%) | Mixing, curing | Moderate traffic, dry areas | | Lime-Flyash Roads | Lime + flyash + soil | Mixing, compaction | Industrial areas, waste utilization |

• Features: Simple construction, use of local materials, regular maintenance.

[!TIP]

Low-cost roads require proper drainage and periodic maintenance to prevent deterioration.

III. AIRPORT ENGINEERING

3.1 Airport Planning & Site Selection

• Factors:

  • Topography: Flat terrain, minimal earthwork.

  • Wind Direction: Prevailing winds along runway; crosswind component < 15 kmph.

  • Approach Area: Obstacle-free zone (clearance of obstacles in approach path).

  • Soil: Good bearing capacity, low settlement.

  • Utilities: Availability of water, electricity, sewage.

  • Environmental: Noise pollution, wildlife hazards.

  • Expansion: Room for future growth.

• Zoning Regulations (as per ICAO):

  • Approach Surface: Tapered area at runway ends.

  • Transitional Surface: Along sides of approach surface.

  • Horizontal Surface: 150 m above runway elevation.

  • Conical Surface: Outer boundary.

  • Inner Horizontal Surface: 150 m radius around runway.

  • DiagramSEARCH: airport zoning surfaces ICAO

[!TIP]

Runway orientation is chosen based on wind rose diagram to minimize crosswinds.

3.2 Runway Design

Geometrical Elements

• Length: Depends on aircraft requirements, altitude, temperature, gradient.

• Width: Based on aircraft wheel span; typically 45–60 m for large airports.

• Orientation: Aligned with prevailing wind; wind rose diagram used.

• Gradient: Maximum 1% (1.5% for code 4E+), effective gradient considered.

• Safety Areas: Runway end safety areas (RESA) 90 m × 90 m.

• Shoulders: 0.5–1.5 m on each side.

Runway Length Correction

• Standard Conditions: Sea level, ISA temperature (15°C), no wind, no gradient.

• Corrections:

  1. Elevation Correction:

$$\Delta L_e = L \times \left( \frac{\text{elevation (m)}}{300} \times 0.07 \right)$$

2. Temperature Correction:

$$\Delta L_t = L \times \left( (\text{reference temperature} - 15) \times 0.01 \right)$$

3. Gradient Correction:

$$\Delta L_g = L \times (G \times 0.001)$$

 ($G$ = effective gradient in %)

• Corrected Length:

$$L_{\text{corrected}} = L_{\text{standard}} \times (1 + \Delta e) \times (1 + \Delta t) \times (1 + \Delta g)$$

or add corrections additively: $$\displaystyle L_{\text{corrected}} = L_{\text{standard}} (1 + \Delta e + \Delta t + \Delta g) $$.

• Numerical Example (NOV 2023):

  $$\displaystyle L_{\text{standard}} = 2000 $$ m, elevation = 300 m, reference temp = 33.05°C, gradient = 0.25%.

  $$\displaystyle \Delta e = (300/300) \times 0.07 = 0.07 $$ (7%)

  $$\displaystyle \Delta t = (33.05 - 15) \times 0.01 = 0.1805 $$ (18.05%)

  $$\displaystyle \Delta g = 0.25 \times 0.001 = 0.00025 $$ (0.025%)

  $$\displaystyle L_{\text{corrected}} = 2000 \times 1.07 \times 1.1805 \times 1.00025 \approx 2000 \times 1.263 = 2526 $$ m.

Aircraft Characteristics Affecting Design

[!TIP]

Runway length is corrected for elevation, temperature, gradient; always use effective gradient (sum of algebraic gradients).

3.3 Airport Capacity & Delay

• Airport Capacity: Maximum number of aircraft movements (arrivals + departures) per hour under given conditions.

• Factors Affecting Capacity:

  • Runway Configuration: Single, parallel, intersecting runways.

  • Aircraft Mix: Different sizes and speeds cause separation variations.

  • Air Traffic Control (ATC): Efficiency of sequencing, radar availability.

  • Weather: Visibility, wind, precipitation.

• Delay: Difference between scheduled and actual arrival/departure time; caused by capacity constraints, ATC, weather.

[!TIP]

Capacity is often expressed in movements/hour/runway; typical values: 30–60 for single runway.

3.4 Airport Lighting & Aids

Runway Lighting

• Threshold Lights: Green (approach end), red (far end).

• Edge Lights: White (runway edges), yellow last 600 m.

• Centerline Lights: White (except last 900 m: alternating red/white).

• Touchdown Zone Lights: White (first 900 m).

• Approach Lighting System (ALS): Provides visual guidance; types: ALSF-1, ALSF-2.

Taxiway Lighting

• Edge Lights: Blue.

• Centerline Lights: Green.

Rotating Beacon

• Purpose: Airport identification at night; white and green light.

Instrument Landing System (ILS)

• Components:

  • Localizer: Horizontal guidance (course).

  • Glideslope: Vertical guidance (path).

  • Marker Beacons: Distance markers (outer, middle, inner).

• Function: Precision approach in low visibility.

Precision Approach Radar (PAR)

• Purpose: Provides both azimuth and elevation guidance; used where ILS not available.

• Operation: Ground-based radar tracks aircraft, controller gives instructions.

[!TIP]

ILS categories (CAT I, II, III) based on decision height and visibility; CAT III allows zero visibility landing.

3.5 Other Airport Elements

Taxiway

• Purpose: Connect runway to apron, allow aircraft movement.

• Design Speed: 30–50 kmph.

• Width: Based on aircraft wheel span; typically 23–46 m.

• Shoulders: 1.5–3 m.

Apron/Gate

• Purpose: Parking, loading/unloading, servicing.

• Layout Considerations: Gate spacing, taxiway access, terminal building location.

Wind Rose Diagram

• Construction: From wind data (speed, direction); plotted on polar graph.

• Types:

  • Speed Wind Rose: Shows frequency of wind speeds from each direction.

  • Direction Wind Rose: Shows direction distribution.

  • Speed-Direction Rose: Combines both.

• Application: Determine runway orientation to minimize crosswind component; select runway with wind within ±15° of heading.

[!TIP]

Runway orientation is chosen such that crosswind component < 15 kmph for >95% of the time.

IV. TRAFFIC ENGINEERING & SAFETY

4.1 Traffic Studies & Data Collection

Speed Studies

• Spot Speed: Instantaneous speed at a point; measured by radar gun.

• Running Speed: Average speed over a stretch, excluding stops.

• Time-Mean Speed: Arithmetic mean of spot speeds.

• Space-Mean Speed: Harmonic mean of spot speeds; used for travel time.

• Average Travel Speed: Distance/time including stops.

• Methods: Radar, pneumatic tubes, LIDAR, video detection.

Origin-Destination (O-D) Study

• Purpose: Understand travel patterns, plan facilities, forecast traffic.

• Uses: Trip generation, distribution, mode choice, assignment.

• Methods:

  • Home Interview: Detailed, expensive.

  • Roadside Interview: At cordon lines.

  • Postal Survey: Mailed questionnaires.

  • Telephone Survey: Cost-effective.

  • Automatic: Number plate recognition.

Parking Studies

• Purpose: Determine demand, design parking facilities, evaluate policies.

• On-Street Parking:

  • Angle Parking: 45°–90°; high capacity, hazardous.

  • Parallel Parking: 0°; safe, low capacity.

  • Off-Street: Parking lots, garages; higher land use.

[!TIP]

Space-mean speed is always less than time-mean speed for same data.

4.2 Traffic Markings

[!TIP]

Yellow markings indicate no parking and hazards; white for lane control.

4.3 Road Lighting

• Objectives: Improve safety at night, reduce accidents, enhance security, extend usable hours.

• Design Factors:

  • Luminance (cd/m²): Brightness of road surface.

  • Illuminance (lux): Light falling on surface.

  • Uniformity Ratio: Min/Max luminance.

  • Glare Control: Limit discomfort and disability glare.

  • Mounting Height: Affects spacing and uniformity.

  • Spacing: Based on luminaire characteristics, road width.

[!TIP]

Luminance is more critical for driver’s perception than illuminance; design for road surface brightness.

4.4 Intersections & Grade Separation

At-Grade Intersections

• Types:

  • T-Intersection: Three legs.

  • Y-Intersection: Three legs at acute angle.

  • Cross (X) Intersection: Four legs.

  • Staggered: Two T-intersections close.

  • Multi-leg: More than four legs.

• Advantages: Low cost, simple.

• Limitations: Conflict points, delays, accidents.

Grade-Separated Intersections

• Types:

  • Flyover (Overpass): One road over another.

  • Underpass: One road under another.

  • Cloverleaf: Loop ramps for free-flow turns.

• Advantages: No conflicts, high capacity, speed.

• Limitations: High cost, land, maintenance, pedestrian inconvenience.

[!TIP]

Cloverleaf has weaving sections; diamond interchange is simpler for minor roads.

V. HIGHWAY ADMINISTRATION, STANDARDS & SHORT NOTES

5.1 Highway Classification

• Based on Function (IRC):

  • Expressways: Controlled access, high speed.

  • National Highways (NH): Connect major cities, ports.

  • State Highways (SH): Connect state capitals, important cities.

  • Major District Roads (MDR): Connect district headquarters.

  • Other District Roads (ODR): Connect production centers, markets.

  • Village Roads (VR): Rural connectivity.

• Based on Traffic Volume: Light, medium, heavy.

• Based on Speed: Low (< 40 kmph), medium (40–80 kmph), high (> 80 kmph).

5.2 Institutional Bodies (Indian Context)

[!TIP]

IRC codes are mandatory for highway design in India; CRF finances National Highways.

5.3 Pavement Joints (Rigid Pavement)

[!TIP]

Dowel bars are smooth and round (for expansion); tie bars are deformed (for contraction/longitudinal).

5.4 Other Recurring Short Note Topics

Off-Tracking

• Definition: Lateral deviation between paths of front and rear wheels during turn.

• Calculation:

$$\text{Off-tracking} = \frac{L^2}{2R}$$

where $L$ = wheelbase (m), $R$ = radius of turn (m).

• Example (NOV 2023): $$\displaystyle L = 6.5 $$ m, $$\displaystyle R = 32 $$ m → Off-tracking = $$\displaystyle \frac{6.5^2}{2 \times 32} = \frac{42.25}{64} = 0.66 $$ m.

Trip Distribution

• Concept: Second step in transportation planning; allocates trips from production to attraction zones.

• Models: Gravity model (most common), growth factor model.

• Equation (Gravity): $$\displaystyle T_{ij} = k \frac{P_i^\alpha A_j^\beta}{f(C_{ij})} $$

  where $$\displaystyle T_{ij} $$ = trips from $i$ to $j$, $$\displaystyle P_i $$ = production, $$\displaystyle A_j $$ = attraction, $$\displaystyle C_{ij} $$ = travel cost, $f$ = impedance function.

Classification of Airports (ICAO)

• Based on runway length and aircraft wingspan (code number 1–4, letter A–F).

• Example: Code 4E → Runway length ≥ 1800 m, wingspan 52–65 m (e.g., Boeing 767).

Runway Threshold Lighting

• Runway End Identifier Lights (REIL): Pair of synchronized flashing lights at threshold.

• Threshold Lights: Green (approach end), red (far end).

• Purpose: Identify runway threshold in low visibility.

[!TIP]

Off-tracking increases with wheelbase and decreases with larger radius; critical for designing turning paths at intersections.

END OF UNIT 2
Always refer to latest IRC codes and standard textbooks (Khanna, Khurmi) for numerical problems and design details.