Transportation Engineering- II (CE-502) - Unit 4 Short Notes

UNIT 4: TRANSPORTATION ENGINEERING-II (CE-502)

Exam-Focused Short Notes | Based on RGPV Past Papers (2023-2025)

I. HIGHWAY GEOMETRIC DESIGN & ALIGNMENT

1.1 Horizontal Alignment

• Purpose: To provide a smooth, safe transition between straight sections (tangents) of a road, accommodating vehicle dynamics and driver comfort.

• Types of Curves:

  • Simple Circular Curve: Single constant radius. Most common.

  • Compound Curve: Two or more circular curves with different radii on same side (used in mountainous terrain).

  • Reverse Curve: Two circular curves in opposite directions (requires transition curve between them).

  • Transition (Spiral) Curve: Radius varies uniformly from infinity to that of the circular curve (or vice-versa). Provides gradual introduction of centrifugal force.

• Design of Superelevation (e):

  • Purpose: To counteract centrifugal force by raising the outer edge of the carriageway.

  • Derivation: For equilibrium, $$\displaystyle e + f = \frac{V^2}{gR} $$, where $f$ is side friction factor.

  • IRC Formula (for mixed traffic):

$$e = \frac{V^2}{127R} + 1.5\% \text{ (minimum)}$$

Where $V$ is design speed (kmph), $R$ is radius (m).

*   **Maximum Superelevation:** 7% (plain/rolling), 10% (mountainous) as per IRC.

*   **Minimum Superelevation:** 1.5% (for drainage).

• Widening of Carriageway on Curves:

  • Purpose: To accommodate off-tracking and provide psychological width.

  • Total Widening ($$\displaystyle W_T $$):

$$W_T = w + \frac{l^2}{4R}$$

Where $w$ = psychological widening (0.3m for single lane, 0.6m for multi-lane), $l$ = wheelbase, $R$ = radius.

1.2 Sight Distance

• Stopping Sight Distance (SSD): Distance required for a driver to stop safely after seeing an object.

$$SSD = 0.278Vt + \frac{V^2}{254(f \pm i)}$$

(V in kmph, t=2.5 sec, f=0.35 to 0.4)

• Overtaking Sight Distance (OSD): Distance required for a safe overtaking maneuver.

  OSD Formula (IRC):

$$OSD = d_1 + d_2 + d_3 + d_4$$

*   $$\displaystyle d_1 $$: Distance travelled by overtaking vehicle during reaction time (0.7V).

*   $$\displaystyle d_2 $$: Distance while overtaking (0.7V + 2s).

*   $$\displaystyle d_3 $$: Clearance length (6m).

*   $$\displaystyle d_4 $$: Distance travelled by oncoming vehicle during overtaking (s).

*   **Given:** $V$ = speed of overtaking vehicle (kmph), $$\displaystyle V_b $$ = speed of overtaken vehicle (kmph), $s$ = spacing between vehicles (1.5-2 sec).

• Intermediate Sight Distance (ISD): Usually taken as 2/3 of OSD for two-lane roads.

• Overtaking Zone:

  • Minimum Length: 3 × OSD.

  • Desirable Length: 5 × OSD.

  • Sketch:

    DiagramCANVAS: Overtaking zone showing OSD distance, no-passing markings, and sign posts at start, middle, and end.

1.3 Vertical Alignment

• Summit Curve (Convex): Formed at intersection of two positive gradients. Primary consideration: Sight distance (SSD/OSD). Parabolic shape is most common.

• Sag Curve (Concave): Formed at intersection of two negative gradients. Primary considerations: Sight distance (at night, headlight range), comfort (centrifugal force change), drainage.

1.4 Geometric Design Standards & Off-tracking

• Cross-sectional Elements: Design speed, carriageway width (3.5m per lane), shoulder width, camber (2-4% for cement concrete, 2.5-5% for bituminous), gradient (max 1 in 30 for plain, 1 in 20 for rolling, 1 in 15 for mountainous).

• Off-tracking: The phenomenon where the rear wheels follow a path of smaller radius than the front wheels.

  Formula:

$$Off\text{-}tracking (O) = \frac{l^2}{8R} \text{ (for single vehicle)}$$

Where $l$ = wheelbase (m), $R$ = radius of curve (m) negotiated by front wheels.

II. PAVEMENT DESIGN & MATERIALS

2.1 Flexible Pavement Design - CBR Method (IRC:37-2018)

• Step-by-Step Procedure:

  1. Determine CBR value of subgrade soil (soaked, 4-day immersion test).

  2. Select design traffic in terms of cumulative standard axles (CSA) for design life (10-15 years).

  3. Use IRC nomograph or equation to find total pavement thickness ($D$) corresponding to CBR and CSA.

  4. Allocate layer thicknesses based on material quality (higher quality material for lower layers).

  5. Check for shear stress in each layer (using Burmister's theory orIRC equations).

• Sketch:

  DiagramCANVAS: Cross-section of flexible pavement showing subgrade, sub-base, base, and bituminous surface layers with thicknesses D1, D2, D3.

2.2 Rigid Pavement Design - IRC Method (IRC:58-2002)

• Brief Outline:

  1. Determine design wheel load (standard axle load 8170 kg).

  2. Estimate modulus of elasticity of concrete ($$\displaystyle E_c $$) and Poisson's ratio ($\mu$).

  3. Find modulus of subgrade reaction ($k$) from plate bearing test.

  4. Use IRC design charts or ** Westergaard's equations** to compute slab thickness ($h$) for corner, interior, and edge stresses.

  5. Check for flexural stress ($$\displaystyle \sigma_{ct} $$) < allowable flexural strength of concrete.

  6. Design joint spacing (contraction, expansion) and reinforcement (if needed for temperature/friction stresses).

2.3 Pavement Construction Materials

2.4 Pavement Evaluation: Flexible vs. Rigid

III. AIRPORT ENGINEERING

3.1 Aircraft Characteristics & Effect on Design

• Key Characteristics: Wingspan (affects taxiway width, runway width), Tail height (clearance for hangars), Wheel base & Turning radius (affects taxiway design), Approach speed (affects runway length), Cockpit eye height (affects approach slope & obstacle clearance).

• Effect on Design:

  DiagramCANVAS: Sketch showing aircraft on runway/taxiway with dimensions marked (wingspan, wheelbase, tail height) and their influence zones (runway width, taxiway curve radius, obstacle clearance surface).

3.2 Runway Length Correction

• Standard Runway Length ($$\displaystyle L_0 $$): Under ISA (MSL, 15°C, zero gradient, no wind).

• Corrections (Additive):

  1. Altitude Correction: $$\displaystyle L_1 = L_0 \times (1 - \frac{h}{1000} \times 0.02) $$ (h in m)

  2. Temperature Correction: First find Reference Temperature ($$\displaystyle T_R $$) = $$\displaystyle T_{max} + \frac{A}{3} $$ (A=annual average daily temperature range). Then $$\displaystyle L_2 = L_1 \times \frac{T_R + 15}{15 + 15} $$.

  3. Gradient Correction: $$\displaystyle L_3 = L_2 \times (1 + \frac{\sum \text{effective gradient}}{100}) $$ (Effective gradient = algebraic sum of gradients/ total length).

• Corrected Runway Length: $$\displaystyle L = L_3 $$

  Final Formula:

$$L = L_0 \times \left(1 - \frac{h}{1000} \times 0.02\right) \times \frac{T_R + 15}{30} \times \left(1 + \frac{\text{Eff. Grad.}}{100}\right)$$

3.3 Airport Capacity & Delay

• Airport Capacity: Maximum number of aircraft movements (arrivals+departures) that can be handled per unit time under existing conditions.

• Factors Affecting Capacity:

  • Runway Configuration: Single, parallel, intersecting, etc.

  • Aircraft Mix: Proportion of heavy vs. light aircraft (affects separation).

  • Air Traffic Control (ATC): Efficiency of separation standards.

  • Weather: Visibility, wind, precipitation.

  • Taxiway Layout & Exit Design.

3.4 Airport Site Selection & Zoning

• Site Selection Factors: Topography (relatively flat), Wind direction (prevailing wind along runway), Obstructions (clear approach zones), Accessibility (to city), Expansion potential, Soil conditions, Environmental impact.

• Zoning Regulations (Approach Zones):

  DiagramSEARCH: "ICAO airport zoning approach surfaces diagram"

  • Approach Surface: Tapered area at runway end for obstacle clearance.

  • Conical Surface: Sloping surface around airport.

  • Horizontal Surface: Horizontal plane at airport elevation.

  • Transitional Surface: Connects approach/horizontal to conical.

  • Purpose: To control height of obstructions for safe aircraft operations.

3.5 Airport Lighting & Visual Aids

• Runway Lighting System:

  DiagramSEARCH: "runway edge lights threshold lights touchdown zone lights diagram"

  • Threshold Lights: Green (arrival end), Red (departure end).

  • Edge Lights: White (runway edges), Yellow (last 2000m or half runway).

  • Centerline Lights: White (except last 900m: alternating red/white, last 300m: red).

  • Touchdown Zone Lights: White (rows at 30m intervals).

• Rotating Beacon: High-intensity light rotating to indicate airport location (color: white/green for civil, white/yellow for military).

• Runway Threshold Lighting: See above.

3.6 Airport Navigation Aids

• Instrument Landing System (ILS): Provides precision guidance.

  • Localizer: Provides lateral guidance (course line along runway centerline).

  • Glideslope: Provides vertical guidance (typically 3° slope).

  • Marker Beacons: Provide position fixes (Outer, Middle, Inner markers).

• Precision Approach Radar (PAR): Ground-based radar providing both lateral and vertical guidance to pilot via voice instructions until visual contact.

3.7 Airport Classification

• ICAO/FAA: Based on runway length and aircraft wingspan (Code 1 to 4, e.g., 4E, 3C).

• Based on Traffic: Primary, Commercial, General Aviation, Relief airports.

• Based on Function: International, Domestic, Regional, etc.

IV. TRAFFIC ENGINEERING & STUDIES

4.1 Traffic Studies & Analysis

• Speed Studies:

  • Spot Speed: Speed at a specific point (measured by radar/enumerator).

  • Running Speed: Average speed while moving (excluding stops).

  • Time-Mean Speed ($$\displaystyle V_t $$): Arithmetic mean of speeds of vehicles at a point.

$$V_t = \frac{\sum v_i}{n}$$

*   **Space-Mean Speed ($$\displaystyle V_s $$):** Harmonic mean of speeds over a length. 

$$V_s = \frac{n}{\sum (1/v_i)}$$

*   **Average Speed:** Usually space-mean for a section.

*   **Method:** Enumerator with stopwatch, radar gun, pneumatic road tubes.

• Origin-Destination (O-D) Study:

  • Purpose: To know trip origins, destinations, purposes, modes.

  • Methods:

    1. Home Interview: Most accurate, expensive.

    2. Roadside Interview: At cordon lines.

    3. Registration Number Method: At selected points.

    4. Postal Survey, Telephone Survey.

  • Uses: Trip generation & distribution forecasting, planning new facilities, traffic assignment.

• Trip Distribution: Allocating trips from origins to destinations. Factors: land use, income, travel time, cost.

4.2 Traffic Control Devices

• Traffic Markings:

  | Type | Examples | Uses | | :--- | :--- | :--- | | Longitudinal | Center line, edge line | Separate traffic flows, define pavement edge. | | Transverse | Stop line, crosswalk, pedestrian crossing | Indicate stopping points, crossing zones. | | Object Markers | Marker posts, hazard markers | Highlight obstructions (islands, bridges). | | Hazard Markings | Chevrons, hatch markings | Warn of changing alignment or narrowing. |

• Grade Separated Intersections:

  • Definition: Intersections where conflicting movements are separated by vertical alignment (flyover/underpass).

  • Types: Flyover (overpass), Underpass.

  • Advantages: No conflict points, high capacity, uninterrupted flow.

  • Limitations: Very high cost, long construction time, large land requirement, not suitable for all terrains.

4.3 Parking Studies

• Purpose: Determine parking demand, turnover, duration, occupancy for planning facilities.

• On-Street Parking Methods:

  • Parallel: Along curb. Most space-efficient, causes least obstruction.

  • Angle (30°-60°): Easier parking/merging, more space than perpendicular.

  • Perpendicular (90°): Highest capacity per unit width, but requires more street width.

V. SOIL STABILIZATION & LOW-COST ROADS

5.1 Soil Stabilization

• Scope & Objectives: Improve soil properties (strength, durability, volume stability) to serve as subgrade/sub-base/base. Reduce construction cost by using local materials.

• Mechanical Stabilization: Physical process of mixing two or more soil grades to achieve desired gradation and Plasticity Index (PI). No binder added. Aims to get dense, well-graded mass.

5.2 Low-Cost Roads

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

• Types:

  • Earth Roads: Natural surface, only shaping and compaction.

  • Gravel Roads: Aggregate surface layer on prepared subgrade.

  • Improved WBM: Better quality control than traditional WBM.

  • Soil-Cement Roads: Soil mixed with cement (5-8%) as binder.

  • Lime-Flyash Roads: Stabilized with lime and flyash.

VI. HIGHWAY ENGINEERING SURVEYS & MISCELLANEOUS

6.1 Engineering Surveys for Highway Location

1. Map Study: Topographic maps to identify feasible corridors.

2. Preliminary Survey: Reconnaissance to select 2-3 alternate alignments.

3. Detailed Survey: Topographic, soil, drainage surveys for selected alignments.

4. Location Survey: Final alignment pegging, cross-sections, profiles.

• Use of Map Study: Initial screening based on drainage patterns, settlements, terrain, existing features.

6.2 Road Classifications & Administration (India)

• Classification (as per Nagpur Plan):

  • National Highways (NH): Connect major ports, state capitals, etc.

  • State Highways (SH): Connect district HQs, important cities within state.

  • Major District Roads (MDR): Connect production centers, markets.

  • Other District Roads (ODR): Connect smaller centers.

  • Village Roads (VR): Connect villages to each other and to higher systems.

• Organizations:

  • IRC (Indian Road Congress): Formulates codes & standards (IRC:37, 58 etc.).

  • CRRI (Central Road Research Institute): Research & development.

  • CRF (Central Road Fund): Funding source for road development.

  • HRB (Highway Research Board): Coordinates research (now under NHAI/CRRI).

6.3 Pavement Joints (Rigid Pavement)

• Objectives: Allow for expansion/contraction, control cracking, construct in panels.

• Types & Sketches:

  DiagramCANVAS: Sketches showing: (a) Expansion joint (with dowel bars & filler), (b) Contraction joint (with tie bars), (c) Construction joint (keyed or dowelled), (d) Longitudinal joint (with tie bars).

  • Expansion Joint: Full-depth joint with compressible filler. Dowel bars (smooth, round) allow movement & load transfer.

  • Contraction Joint: Partial-depth groove or saw cut. Tie bars (deformed) hold faces together.

  • Construction Joint: Formed when work stops. May use keyways or dowels.

  • Longitudinal Joint: Between lanes. Uses tie bars.

• Dowel Bars vs Tie Bars:

  • Dowel Bars: Load transfer across joints (expansion/contraction). Smooth, round, placed perpendicular to joint.

  • Tie Bars: Hold faces together (longitudinal/contraction joints). Deformed, placed parallel to surface.

END OF UNIT 4 NOTES