1. Chapter 1 Historical Aspects of Highway Development and Planning
Highway Engineering

2. Roads were in existence from pre-historic times
Roads were in existence from pre-historic times. The earliest roads were in Egypt and in the Indus valley.
Romans were pioneers in road construction; they built roads with layers of stones set in lime mortar.
Tresaguet in France, and Telford and Macadam in England, developed road construction with base course, intermediate course and surface course consisting of broken stone of different sizes.
Highway Engineering

3. Several road development plans such as the Nagpur plan, Bombay plan and Lucknow plan were implemented in 20-year periods in India during the pre- and post-independence eras. The present road network in India consists of rational highways, state highways, major and minor district roads, and village roads. Road development plans are made for a design period of 25 to 30 years. Urban roads are constructed with different patterns such as the grid-iron, radical and hexagonal types.
Highway Engineering

4. Planning is done from the 'whole to the part' of a country; the master plan is phased and priorities are fixed based on the principle of maximum utility during the design period.
Highway Engineering

5. Chapter 2 Highway Alignment and Surveys
Highway Engineering

6. 'Alignment' means laying out the centre-line of a proposed highway on the ground. The important criteria in choosing a good alignment are minimum length of the route, operational convenience, safety and economy.
Horizontal curves will be needed wherever a change of direction is required; similarly, vertical curves are needed wherever a change of gradient is required depending upon the terrain.
Highway Engineering

7. Smoothening alignment in horizontal and vertical plane
The controlling factors for alignment are topographical features, obligatory points, geometric design aspects, and cross-drainage needs.
Besides map study, the important engineering surveys needed for highway alignment and location are the reconnaissance survey, preliminary survey and location survey.
Highway Engineering

8. Traversing and levelling are the conventional surveying methods used; modern methods involve the use of a Total station, remote sensing, GPS and GIS for important projects.
Detailed engineering drawings accompanied by a project report, are required for the implementation of any major highway project.
Environment impact assessment (EIA) may also be needed for such major jobs.
Highway Engineering

9. Chapter 3 Geometric Design of Highways
Highway Engineering

10. 'Geometric design' of highway involves the design of certain physical and visual elements relating to the highway and the road user for maintaining speed coupled with safety.
Nature of the terrain, vehicle and traffic characteristics, and design speed are the important criteria governing geometric design.
Carriageway width is 3.75 m for single lane and 7 to 7.5 m for double lane. For multi-lane highways, each lane should be 3.5 m.
Highway Engineering

11. Transverse slope of pavement from the crown on to both sides is called 'Camber'; this helps top drain off rain water. Rainfall and pavement surface characteristics govern the camber, which may range from 1 in 325 to 1 in 60.
For safe driving, a certain distance of the highway should be visible to the driver; this is called the "sight distance". Stopping sight distance is that required to enable a driver to stop a head of an obstruction; overtaking sight distance is that required for safe overtaking of a slow-moving vehicle. Design speed, driver's reaction time, pavement friction and longitudinal gradient of the highway are needed to determine the required sight distance.
Highway Engineering

12. For a sloping stretch, V: Design speed in km/h
t: Driver's reaction time in seconds
f: pavement friction coefficient
For a sloping stretch,
g: gradient in per cent (g vertical to 100-horizontal)
+ sign for ascending grade
sign for descending grade
V: Design speed or speed of overtaking vehicle (km/h)
Vs: Speed of slow-moving vehicle (km/h)
Highway Engineering

13. s: minimum spacing between vehicles (m)
t: hesitation time for overtaking driver (2 to 3 seconds)
T: time taken for the overtaking manoeuvre (seconds)
A: acceleration in km/h/s
[The relevant IRC standard is IRC: ]
In the horizontal alignment where change of direction is needed, a simple circular curve along with transition curves (at both ends for gradual change curvature) is used for safety and comfort.
'Superelevation' means raising of the outer edge of the pavement over the inner on horizontal curves, in order to prevent overturning of the vehicle because of the centrifugal force acting on it while traversing a circular curve at a constant speed.
Pavement friction also counteracts the ill-effects of the centrifugal force.
Highway Engineering

14. If both superelevation and friction are considered,
V: design speed (km/h)
R: Radius of curve (m)
e: rate of superelevation
f: friction coefficient
If superelevation alone is considered,
Highway Engineering

15. a: Permissible rate of change of radial acceleration
The actual superelevation, E is obtained by multiplying e by the width of the carriageway. The limiting values of e depend upon the nature of the terrain (7 % for plain and rolling terrain and 10% for hilly terrain).
Length of transition required may be got either by the concept of permissible rate of change of radial acceleration or permissible rate of introduction of superelevation (time-rate or spatial-rate).
V: speed (km/h)
R: Radius of curve (m)
a: Permissible rate of change of radial acceleration
[taken as 0.3 m/s3].
Highway Engineering

16. Time-rate of introduction of cant or superelevation:
But IRC recommends
Time-rate of introduction of cant or superelevation:
where G: Width of pavement
rt: time-rate of introduction of cant (mm/s)
The cubic parabola and lemniscate are commonly used for transition curve.
[Rotation of the pavement about the centre-line is commonly used for gradual introduction of superelevation along the transition.]
In view of the rigid wheel base of vehicles, extra width of pavement is provided on curves for safety.
Highway Engineering

17. V: Design speed
R: Radius of curve
n: number of lanes
l: length of wheel base
Longitudinal gradients will be needed in the vertical alignment of a road, depending on the nature of the terrain. Certain minimum gradient is need for drainage. Ruling, limiting and exceptional gradients are specified by the IRC for different types of terrains. Grade compensation is practised on horizontal curves to compensate the loss of tractive effort.
IRC recommends compensation of percent, R being the radius of the curve in metres.
Vertical curves are of two-types-Summit curves and sag curves. The criteria for the determination of the length of a vertical curve are the centrifugal effect and visibility.
Highway Engineering

18. Summit curves: Sight distance is the important criterion
Summit curves: Sight distance is the important criterion. The sight distance may be less or more than the length of the vertical curve; both cases are to be checked.
for S < L
Here, G = algebraic difference of grades.
S = Sight distance (m)
H = height of driver's eye above road surface (usually 1.2 m)
h = height of obstruction above road surface (usually 0.15 m)
Thus, for S < L
Highway Engineering

19. Sag Curves Rider comfort criterion:
(based on rate of change of radial acceleration of 0.6 m/s3)
Head-light sight distance criterion:
for S < L
[Parabolic arc is preferred to vertical curves. Tangent corrections method is used for setting out in the field.]
for S > L
Highway Engineering

20. Chapter 4 Traffic Engineering and Traffic Regulation
Highway Engineering

21. Road-user characteristics: Psychological factors
Traffic engineering : It is the science of measuring traffic and travel, the study of the basic laws relating to traffic flow and generation, and application of this knowledge to the generation, and application of this knowledge to the professional practice of planning, designing and operating traffic systems to achieve safe and efficient movement of persons and goods.
Road-user characteristics:
Psychological factors
Perception , intellection , emotion and volition (PIEV theory)
Attitude to traffic regulations
Driving skills, intelligence and maturity
Physiological factors
Vision
Hearing
Physical strength (in the case of heavy vehicles)
Highway Engineering

22. Environmental factors Weather Time of the day
Land use in the vicinity of the highway (distraction to the driver's attention)
Vehicle characteristics:
Size, weight and speed of the vehicle: Size and weight of the Design vehicle are specified by the IRC. Design speed of the vehicle is also given by the IRC for different types of highway. Skid resistance or friction coefficient may be determined by conducting a braking test.
V: speed
f: skid resistance or friction coefficient
s: braking distance to step the vehicle.
Highway Engineering

23. The concept of probability and the laws of probability
Also,
a: retardation during braking (m/s2)
g: acceleration due to gravity (9.8 m/s2)
Traffic studies, analysis and interpretation of the data help in the design of geometric design of the highway.
Statistical concepts are useful in the analysis of data from traffic studies.
The concept of probability and the laws of probability
Sample statistics for location:
Mean (or average of a set of observed values)
Median (Middle value of a set)
Mode (Value that occurs with the highest frequency in a sample set)
Highway Engineering

24. Standard deviation of the mean or : n: number of observed values
Sample statistics of dispersion:
Range (Difference between the largest and smallest values in a set)
Standard deviation
is the deviation of a value from the mean of the set.
Standard deviation of the mean or :
n: number of observed values
: mean of a set
This is also called 'Standard Error'
Variance: Square of the standard deviation
Highway Engineering

25. Normal distribution: Standard probability curve in the analysis of a continuous variable
Weight of an observation: A number which indicates the relative degree of reliability or trustworthiness of an observed value.
The most probable value: It is the value of a variable set of observations, which is more likely to be correct than any other value. For observations of equal weight, it is the arithmetic mean of the set; for weighted observations, it is the weighted arithmetic mean of the set.
Highway Engineering

26. Traffic studies Principle of least squares
The most probable value of a quantity is such that the sum of the squares of the residuals is a minimum.
The most probable value of a quantity is such that the sum of the weighted squares of the residuals is a minimum.
Traffic studies
Speed studies
Journey time and delay studies
Origin and destination studies
Traffic volume studies
Traffic flow characteristics
Traffic forecasting
Parking studies
Accident studies
Highway Engineering

27. Speed studies: Instantaneous speed of a vehicle at a specified location to assess traffic congestion for locating traffic signals.
Running speed: Average speed of a vehicle over a given stretch of highway while the vehicle is actually in motion. (Delays are not considered.) It is used to assess traffic capacity of highways.
Operating speed: It is the sustained running speed at which a vehicle can travel under the existing traffic and environmental conditions-to now the overall efficiency of a highway.
Overall or journey speed: Effective speed with which a vehicle covers a particular route between two terminals. Total distance divided by total time taken including all delays, but excluding voluntary stoppages if any.-to assess the adequacy of an existing road network as also the efficiency of the improvement measures before and after implementation – for cost-benefit analysis.
Highway Engineering

28. Methods of measuring spot speed:
Direct observation of time-enoscope, pressure contact tubes
Radar speed mater
Electronic speed meter
Photographic methods.
Analysis of spot speed data: Besides mathematical analysis of the frequency distribution table, graphical analysis of the frequency distribution curve of the data is also used.
Cumulative speed distribution curve: with speed versus percent vehicles at or below the speed.
85 percentile speed: The speed below which 85% of the vehicles are moving at the point on the highway. In other words, only 15% of the vehicles exceed this speed.) This is considered to be the safe speed limit under the existing conditions in this zone.
However, 98 percentile speed is used for geometric design.
15 percentile speed is taken as the minimum speed on major highways.
Highway Engineering

29. Presentation of traffic volumes and variations is very useful.
Traffic Volume Studies
Traffic census or traffic surveys: Types of traffic, size and weight, traffic per hour and per day, including seasonal variations.
Traffic volume counts may be manual or by using automatic traffic counters.
Presentation of traffic volumes and variations is very useful.
Annual Average Daily Traffic (AADT) is useful in the design of the facility and highway capacity. Also useful for traffic regulation and control.
For design, the 30th hourly traffic volume of the AADT plot is taken. (Since this volume is exceeded only 29 times in the whole yea, congestion will occur only on these few occasions.)
Highway Engineering

30. Traffic density (vehicles/km)
Traffic forecasting: Forecasting future traffic for a design period is needed for the design of a highway facility.
Forecast methods:
Based on past trends
Using analytical or mathematical models
A ten-year design period is considered reasonable.
Accident studies: Road accidents may be caused in several ways:
Road conditions and faulty geometric design
Road user' non-compliance of traffic rules and regulations, rash driving, and drunken driving
Mechanical defects of vehicles
Unfavourable conditions of weather
Miscellaneous reasons such as stray animals, unmanned railway level crossings, large hoardings affecting visibility and distracting the driver's attention.
Highway Engineering

31. Accident records: Collecting and recording of details of road accidents is necessary to implement preventive and curative measures to avert accidents, which could lead to loss of property and life, besides causing traffic breakdowns and traffic jams. Scientific analysis of accidents using the laws of motion and conservation of momentum is preformed. Collision of a vehicle with a parked vehicle and collision of two vehicles approaching in perpendicular directions may be analysed to determine their original speeds.
Preventive measures
Engineering measure: Proper design of geometric elements, speed control, maintenance of road as well as the vehicles.
Enforcement measures: Traffic regulation and control measures, channelisation of different types of traffic.
Education measures: Education on road safety, use of helmets, use of mass media for inculcating traffic discipline and awareness.
Highway Engineering

32. Traffic regulation and control
(a) Traffic signs
(b) Road markings
(c) Traffic signals
(d) Traffic control aids such as speed breakers
(e) Traffic islands and channelisation
Traffic signs
Cautionary or Warning signs
Regulatory or Mandatory signs
Informatory signs
Cautionary signs: Equilateral triangle shape
Example: Right turn ahead
Highway Engineering

33. Informatory signs: Rectangular shape Example: Petrol pump (ahead)
Regulatory signs: Circular shape
Example: Speed limit
Informatory signs: Rectangular shape
Example: Petrol pump (ahead)
Road Markings
These are lines, patterns, words, painted on or set into the carriageway, for controlling, warning, guiding or informing the road users to promote road safety. Thermoplastic paints are used for better visibility. Night visibility can be enhanced by using minute glass beads set in the markings to produce a retro-reflective surface. Studs, and metal and plastic inserts are also used.
Highway Engineering

34. Signals with coloured lights: RED – Stop GREEN – Go
Traffic signals
Installed at road intersections to avoid conflicting movements of vehicles approaching from different directions.
Signals with coloured lights: RED – Stop GREEN – Go
AMBER – Get ready indication as a transition for clearance of moving vehicles. Flashing Amber signal indicates 'Proceed with caution'.
(a) Carriageway markings:
(b) Object markings:
Centre line of the highway
Markings on physical obstructions
Traffic lane lines
Traffic islands
Pavement edge lines
Guard rails
Pedestrian markings
kerbs
STOP lines
Speed breakers
Route direction arrows
Rumble strips
Markings at approaches to intersections
Traffic sign and signal supports
Parking limits
Utility poles
Bus stops
Word messages
Highway Engineering

35. Traffic-activated signals Co-ordinated signals
Types of signals
Fixed-time signals
Traffic-activated signals
Co-ordinated signals
Signals are set to repeat in predetermined time cycles for each of the phases based on the expected traffic on the intersecting roads. Automatic electrically operated signals are the simplest type.
A simple signal face
Highway Engineering

36. Traffic-actuated signals
Detectors placed on the carriageway ahead of the stop-line; these are actuated by approaching vehicles to flash or extend green based on traffic demands. The right of way can be assigned by a computer system programmed appropriately.
Co-ordinated signals
These are signal systems along a city thoroughfare with intersections at frequent intervals, co-ordinated in such a way that a vehicle moving along the thoroughfare at normal speed need not have to stop at every intersection; it gets a 'through band' with minimum delay, resulting in increased capacity along the route.
Design of traffic signals:
The methods commonly used are:
(a) Trial cycle method
(b) Webster's minimum delay method
(c) IRC method (basically the same as Webster's method, but with a few minor variations given by the IRC)
Highway Engineering

37. Traffic effects on environment (a) Air pollution (b) Noise pollution
Highway Capacity
'Saturation flow' is related to highway capacity and denotes the maximum number of vehicles that can pass with minimum space headway. 'Theoretical or basic capacity' of a lane is dependent on speed and minimum space headway between vehicles; the ideal conditions are never realised. 'Practical capacity' is much less than the basic capacity owing to constraints such as driver, vehicle and roadway conditions. 'Passenger Car Unit (PCU)' are used with equivalency factors for different vehicles under mixed traffic conditions involving slow and fast traffic. This is for-convenience in design. These factors are recommended by the IRC.
Traffic effects on environment
(a) Air pollution
(b) Noise pollution
Preventive measures to minimise these are necessary for protecting environment.
Highway Engineering

38. Chapter 5 Highway Intersections
Highway Engineering

39. Intersection: A general area where two or more highways join or cross, with an orderly movement of traffic. Each one of the roads meeting at an intersection is called an 'intersection leg'.
Basic traffic manoeuvres are diverging, merging, crossing and weaving; some or all of these are necessary at an intersection.
Traffic conflicts between vehicles from different streams tend to occur at intersections; the area within which they occur is called 'Conflict area'.
Classification of intersections:
(a) Intersections –at-grade-intersecting legs are all at the same level.
(b) Grade separations- legs are separated in level, supported by a bridge, overpass or an underpass.
Highway Engineering

40. Intersections-at-grade
Visibility or lateral sight distance is an important criterion for safety. Width of carriageway at intersections should be somewhat more than normal depending on the curvature of the roads, for enhanced safety.
Speed-change lanes: Lanes for deceleration on entry and acceleration on exit from an intersection on high-speed highways. These are for safe traffic operations.
Channelisation: Directing the traffic flow at intersections to specified paths by means of makings, traffic islands, etc. Several advantages are there for channelisation-primarily reducing conflicts and conflict areas, resulting in enhanced safety.
Highway Engineering

41. Types: (a) Channelising (b) Divisional (c) Refuge (for pedestrians)
Cross-roads, T-junction and Y-junction are the commonly used layouts in intersections-at-grade.
Traffic islands are raised constructions for guiding traffic along definite paths.
Types: (a) Channelising (b) Divisional (c) Refuge (for pedestrians)
(d) Rotary (for traffic control)
Rotary intersection: A special type at –grade intersection with a large island in the centre for the traffic to weave around and leave in the desired direction. The central island may be circular, elliptical, square, or rectangular, depending upon the number of legs and their relative location or geometry.
Highway Engineering

42. Three-leg interchange: This could be of T-type, Y-type or rotary type.
Grade-separated intersections: The intersecting roads are taken at different levels using a bridge, an overpass or an underpass to support the legs at higher elevations.
Interchange: This is a facility for movement of traffic from one road to another at a different level.
Three-leg interchange: This could be of T-type,
Y-type or rotary type.
Important layouts of grade separations
Diamond type
Partial clover-leaf
Clover-leaf
Rotary type (could be multi-legged) Clover-leaf interchange
These are justified only with high speed, high –volume highway intersections are needed , in view of the large areas required and the prohibitive costs involved.
Highway Engineering

43. Chapter 6 Highway Materials
Highway Engineering

44. Soil or earth material, mineral aggregates such as broken stone and sand, and binder materials like bitumen and cement are the primary materials for road construction.
Since soil is used for subgrade and also acts as the foundation to which traffic loads are ultimately transferred, its engineering behaviour has to be studied. Geotechnical engineering aspects relevant to highway engineering are important in this context.
Soil formation, soil profile, and parent rock have influence on the engineering properties of soil.
In general, soil may be visualised as a three-phase material consisting of solid grains, water and air. For a dry soil, water is about and for a saturated soil, air is absent.
Volume-weight relationships of the soil phases help to establish porosity, void ratio, degree of saturation, and water content and their inter-relationships.
Highway Engineering

45. Index properties of soil Grain specific gravity
Unit weight – dry, saturated and submerged, also in the natural state.
Density index
Grain size distribution: Sieve analysis for coarse fraction and sedimentation analysis for five fraction
Consistency limits and indices of cohesive soils-plastic limit, liquid limit, shrinkage limit, plasticity index
These help in classifying soils into distinct groups with similar engineering properties.
Indian Standard Classification of soil is important from the highway engineering point of view.
Broadly speaking, coarse-grained soils and fine-grained soils have significant differences in engineering properties.
Highway Engineering

46. Permeability is the property by virtue of which soil permits water through its voids. The sharing of load by soil grains and soil water leads to the concept of effective stress and pore water pressure (neutral stress). Seepage through soil leads to seepage forces and critical hydraulic gradients which may affect the stability of embankments,
Settlement analysis requires the concepts of compressibility and consolidation of soil. Total settlement and time-rate of settlement may be determined.
Shearing strength of soil is important in view of its particulate nature. It is characterised by the shear parameters-cohesion (c) and angle of interval friction (), under different kinds of testing and different drainage conditions. This gives an insight into soil behaviour under loading.
Soil compaction by mechanical means of rolling is relevant in the construction of highway embankments and earth dams. The concept of optimum water content for maximum dry density is important in this context.
Highway Engineering

47. Stability analysis of earth slopes is also relevant to highway embankments.
Concepts of stress distribution in soil are relevant to settlement analysis of embankments.
Bearing capacity of soil from the criteria of shear failure and permissible settlement is relevant to the stability of highway subgrade and foundation.
Field tests such as plate load test and standard penetration test give an indirect idea, through correlation, of the bearing capacity of soil.
California Bearing Ratio (CBR) gives an indirect indication of the bearing capacity of soil. This is the basis for one popular method for the design of flexible pavements.
Coefficient of subgrade reaction (the constant of proportionality between pressure and settlement), an index of the subgrade strength, is an important property used in the design of rigid pavements.
Mineral on stone aggregates are important materials used in road construction.
Highway Engineering

48. Shape tests: Flakiness index, Elongation index, and Angularity number.
A study of the desirable properties such as the strength, hardness, toughness, and particle shape is necessary.
Shape tests: Flakiness index, Elongation index, and Angularity number.
Water absorption test (an index of porosity)
Soundness test (for stability under adverse weather conditions)
Crushing value test-compression test on an aggregate sample to assess the loss of material under loading.
Impact value test-resistance to impact or toughness. A dropping weight or tup is used to assess the impact strength.
Abrasion test-resistance to abrasion or hardness is determined by Los Angles abrasion test, standardised by the BIS.
Bituminous materials: Bitumen and tar are the important binder materials in road construction. Their origin, manufacture and desirable properties have to be studied.
Highway Engineering

49. Workability: sufficient fluidity for mixing
Ductility: To avoid cracking
Durability: Little change in viscosity within the usual ranges of temperatures in the locality.
Adhesion: Good affinity to the aggregates
Definitions
Asphalt cement: Binder consisting of bitumen, specially prepared by adding flux oils for the desired quality and consistency for direct use in paving, usually in the hot condition.
Oxidised or blown bitumen: Obtained by running crude bitumen, while hot into a vertical column, and blowing air through it.
Cut-back bitumen: Bitumen dissolved in naphtha or kerosene to increase the workability by lowering the viscosity. [Rapid-curing, Medium-curing, slow-curing types]
Emulsified bitumen: A mixture in which asphalt cement, in a finely dispersed state, is suspended in chemically treated water. [Rapid-setting, Medium-setting, slow-setting types]
Highway Engineering

50. Liquid bitumen: Cut backs in naphtha and kerosene, as also emulsified asphalts.
Flux oil: Liquid bituminous material, used for softening other bituminous materials.
Tests on bitumen
Specific gravity: Needed in bituminous mix design
Solubility: Solubility in carbon disulphide ( 99%)-an indication of absence of mineral water.
Water content: Should be minimal to prevent foaming.
Paraffin scale:  2.5% so as not affect the binding quality.
Viscosity: To assess workability
Penetration: To assess viscosity in an indirect manner.
Softening point: Ring-and-ball test (to prevent softening of the road surface)
Ductility: Ability to deform without cracking.
Highway Engineering

51. Cement and cement concrete
Flash point and fire point: Significant in preventing fire hazards during the preparation of mixes.
Loss on heating: Susceptibility of bitumen to heating during mixing operations for the preparation of paving mixes.
Bituminous mixes
Stability
Durability
Flexibility
Workability
Skid resistance
Economy
Cement and cement concrete
Properties such as workability, setting and hardening, and strength characteristics have to be assessed.
Highway Engineering

52. Chapter 7 Highway Pavement Design
Highway Engineering

53. The important layers of a highway pavement are:
‘Pavement Design’ consists of the design of pavement thickness and that of the supporting courses to transmit the wheel load stresses safely to the foundation soil. The pavement should provide a strong and smooth surface and carry the loads during the design life without excessive deformations that are likely to affect the stability and riding quality of the road.
The important layers of a highway pavement are:
Weaving or surface course
Base course
Sub-base course
Soil subgrade
Structural classification of pavements
Flexible
Rigid
Semi-rigid
Composite
Highway Engineering

54. Factors governing pavement design
Flexible pavement: This derives its strength from the various layers of which it is constructed; the pavement by itself does not have adequate strength to transmit the loads.
Rigid pavement: This derives its capacity to resist loads primarily by virtue of its flexural strength, and consists of cement concrete, plain or reinforced.
Factors governing pavement design
Traffic-related factors: Traffic volume, wheel/axle load, and tyre pressure.
Subgrade strength and material properties
Environmental factors-temperature and rainfall
Traffic Volume estimate
This is based on the number of cumulative standard axles per year, rate of traffic growth, design period, vehicle damage factor and lane distribution factor.
Highway Engineering

55. Ten to 20 years for low-traffic and 20 to 30 years for high-traffic
Design life
Ten to 20 years for low-traffic and 20 to 30 years for high-traffic
[IRC: and IRC: for flexible and rigid pavements, respectively]. This is expressed usually in million standard axles per year (msa). The following procedure is used:
End of construction period:
A: Estimated traffic volume by the end of the road construction period.
P: Present traffic
r: Traffic growth rate
nc: Construction period in years
For flexible pavement,
Highway Engineering

56. (VDF) = Vehicle Damage Factor
This is a multiplication factor used to convert the effect of different commercial vehicles to that of standard axle load. This is calculated from axle load survey.
(LDF) = Lane distribution factor
This is a decimal fraction, which indicates the concentration of placement of wheel load repetitions along a road. In a multi-lane highway, lower concentration of vehicles occurs at the edges; therefore, only a part of the commercial traffic volume is taken as the design traffic volume, on economic considerations. This has to be obtained from appropriate field surveys. In the absence of such data, (LDF) values recommended by [IRC: ] are to be used.
Example: 1.00 for single lane, 0.75 for dual-two-lane, etc.
Highway Engineering

57. For rigid pavement
[The effects of (VDF) AND (LDF) are considered to be insignificant in the case of rigid pavements, and are therefore taken as unity.]
Design of flexible pavements
CBR Method (IRC: & 1984)
The basis for this approach of design of a flexible pavement is the CBR-value of the material of the layer.
IRC:
The thickness of construction is given by a set of curves shown on Slide 59
Highway Engineering

58. Traffic classification
Curve
No. of commercial vehicles per day (exceeding 3 tonnes weight) A
0-15 B
15-45 C
45-150 D E F G
Above 4500
Highway Engineering

59. CBR Design curves (IRC: 37−1970)
[Note: ‘Traffic' denotes the total number of vehicles in both directions. For single-lane roads, the traffic intensity is taken to be twice that for two-lane roads as the whole traffic is concentrated on one lane only. For estimation of future traffic, the growth rate is assumed as 7.5 per cent.]
Highway Engineering

60. IRC Guidelines revised in 1984:
New set of design curves are given relating traffic in msa and the CBR-value to the total thickness of pavement. Also, recommendations are given on the types of pavement materials suitable for various courses-surface, base and sub-base courses.
Highway Engineering

61. IRC Revised Method [IRC: 37-2001 (Second Revision)]
The software PAVE, based on Mechanistic-Empirical principles and developed by the IIT Kharagpur, is recommended to be used.
Design charts as well as recommended prevent composition Tables for different CBR-values ranging from 2 to 10% are available for traffic ranges of 1 to 10 msa and 10 to 150 msa, separately.
The latest Revised guidelines are given in IRC: (Third Revision)
These include alternative materials such as reclaimed asphalt materials; the software IITPAVE, developed by IIT Kharagpur, is recommended to be used.
IRC guidelines for Low-traffic Volume Roads
These are given in the special Publications of the IRC:
IRC SP: and IRC: SP:
Highway Engineering

62. (a) Governing criteria for design:
Design of Rigid Pavements
Involves the design of the thickness of the cement concrete slab comprising the pavement; except for low traffic-volumes and street roads, reinforced cement concrete (RCC) slabs are used.
(a) Governing criteria for design:
Properties of cement concrete (RCC)
Strength-compressive and flexural
Modulus of rupture (around 4 MN/m2 (or 4 kg/cm2)
(E) Elastic modulus (around 3  104 MN/m2 or 3  105 kg/cm2)
(ν) Poisson's ratio (0.15 to 0.20)
Reinforcement details
Temperature changes
(b) Joints in rigid pavements
Transverse joints – Expansion joints, Contraction joints, Warping joints
Highway Engineering

63. Longitudinal joints (hinge joints) Prevent warping
Facilitate load transfer from one slab to another
Construction joints-for convenience in construction
(c) Stresses in pavements
Westergaard's theory
Critical loading positions-interior, edge and corner
Edge stress (IRC: ) (a modification of Westergaards equation):
Corner stress (IRC: ):
Highway Engineering

64.  = Poisson's ratio of concrete (taken as 0.15)
Here,
W = Design wheel load
h = Thickness of slab
 = Poisson's ratio of concrete (taken as 0.15)
l = Radius of relative stiffness
E = Elastic modulus of concrete
k = coefficient (or modulus) of subgrade reaction (from plate load tests)
a = radius of circular area of contact of the wheel load.
b = Equivalent radius of resisting section(at the bottom face of the slot)
b is given as follows:
For
Highway Engineering

65. Warping stress chart for edge stress is given in IRC: 58-2002
Warping stresses due to temperature changes depend on the temperature differential between the top and bottom of the slab, elastic module of concrete, the coefficient of thermal expansion of concrete, and Bradbury's coefficient, which depends on the ratio of free length of slab to the radius of relative stiffness.
Warping stress chart for edge stress is given in IRC:
Bradbury's coefficient, C: 1 3 5 7
 12 C
0.175
0.720
1.030
1.000
Highway Engineering

66. Warping stress chart (IRC: 58-2002)
Highway Engineering

67. This is given in detail ion IRC: 58-2002.
Critical combination of stresses-edge load stress and edge warping stress-is considered for the design of pavement thickness.
The design is basically one of 'trial and error' approach; a tentative thickness is assumed and the critical stresses are computed and checked with the modulus of rupture. The latest approach involves the calculation of 'fatigue life' under the expected number of load repetitions.
This is given in detail ion IRC:
Slab reinforcements are designed to resist cracking.
Different joints and their spacing are to be designed such that they serve the intended purpose.
Load transfer devices such as dowel bars and tie bars are designed to determine their diameter, length and spacing.
Highway Engineering

68. Chapter 8 Highway Construction and Drainage
Highway Engineering

69. (a) Subgrade preparation:
Low-cost roads are constructed of earth, gravel, stabilised earth, or water-bound macadam. For superior and high quality pavements, bituminous and cement concrete roads are used.
The earthwork involved in the road construction consists of subgrade preparation and the formation of embankment.
(a) Subgrade preparation:
This involves excavation of soil or cutting, loosening, removing and transporting of soil to a place where it can be used as a fill material. This includes site clearance, grading and compaction. The relative levels of the natural ground and the formation of the proposed roadway at any particular point along the route determine whether cutting is needed or filling.
(b) Embankment construction:
Soil from borrow pits is transported to the site, laid and compacted to the desired level and density.
Highway Engineering

70. (c) Earth-moving machinery:  Bull-dozer  Rooter  Scraper  Grader
 Trucks, dumpers
Water tankers and sprinklers (for watering)
(d) Compaction equipment
Rolling, ramming, kneading and vibration are the basic processes of compaction
 Smooth-wheeled rollers
 Pneumatic –tyred rollers
 Sheepsfoot rollers
Vibratory equipment
Highway Engineering

71. Stabilised earth roads
Earth road is constructed of earth materials of suitable grading and plasticity characteristics. Materials may be brought from nearby borrow pits, laid and compacted.
Gravel/moorum roads are also similar, but are considered better than earth roads.
Stabilised earth roads
Popular for rural roads with low traffic volume.
(a) Mechanical stabilisation
(b) Stabilisation with additives
Mechanical stabilisation: Blending two or more available earth materials to obtain the desired gradation. Low-grade aggregates may also be used.
Stabilisation with additives
Highway Engineering

72. Stabilisation with additives Lime stabilisation – Soil-Lime
4 to 10% of lime may be added depending on the nature of the soil.
Cement stabilisation – Soil-cement
Cement up to 14% may be added. When the cement content is low, it may be called 'cement-modified' soil.
Bitumen stabilisation – Soil-bitumen
Water bound Macadam (WBM) roads
Aggregates held together by adding water and filler. Broken stone aggregates of basalt, granite, quartzite, etc. are used.
Screenings: to fill voids in the coarse aggregate
General procedure of construction and composition is similar to that for earth and gravel roads,
Serves as a base for superior pavements.
Highway Engineering

73.  Wet-mix macadam is an improvement over the conventional WBM.
Advantages:
Better gradation of aggregates
Faster construction
Denser pavement
Less consumption of quality
Better quality control
Lime-fly-ash concrete, lean cement concrete and dry lean concrete, along with wet-mix macadam, serve as good sub-base/base courses.
Rural roads are constructed of stabilised earth or WBM depending upon the traffic requirements; black top surface dressing is common.
Stabilisation with soft aggregates such as broken brick, kankar and laterite, as recommended by S R Mehra, is popular for rural roads.
Bituminous roads: Superior type suited to heavy and fast traffic.
Highway Engineering

74.  Surface treatments (Prime coat, seal coat)  Penetration Macadam
Different types:
 Surface treatments (Prime coat, seal coat)
 Penetration Macadam
 Bituminous Macadam
 Premix carpet
Bituminous concrete (most superior)
Plant and machinery:
Storage, heating, spraying, mixing, spreading, paving, and finishing can all be done by means of appropriate equipment/machinery.
Concrete pavements: Strongest and the most superior type
Steps in construction:
 Preparation of subgrade
 Formwork
Highway Engineering

75. Mechanised construction
 Proportioning of mix and batching
 Laying
 Compaction
 Joints
 Screeding
 Furnishing
 Curing
Mechanised construction
Fixed-form paver-moves on rails at either end of the pavement.
Slip-form paver-has its own train consisting of spreader, finisher, grader.
Joints in concrete pavements
Expansion joints, contraction joints, warping joints, construction joints, longitudinal joints should be designed appropriate by along with load-transfer devices.
Highway Engineering

76. Very important to ensure the stability and durability of the road.
Highway drainage
Removal of surface and sub-surface water away from the road and subgrade.
Very important to ensure the stability and durability of the road.
(a) Surface drainage
(b) Sub-surface drainage
(c) Cross drainage
Surface drainage:
Estimation of run-off from rainfall
Rational formula (IRC: SP: Revised)
Q = C. i. A
Here, Q = peak run-off (m3/s)
C = coefficient of run-off (ranges from 0.90 for concrete to 0.10 for day with vegetation)
i = Critical intensity of rainfall in cm/h occurring during the time of concentration (tc) for the chosen frequency interval or return period
A = catchment area in hectares
[When the catchment consists of different surfaces with different C-values, weighted coefficient of run-off has to be used.]
Highway Engineering

77. Manning's formula for permissible velocity (V) of flow is used.
n: coefficient of rugosity of the material of the drain
R: Hydraulic mean depth
(A being Area of flow and P the wetted perimeter)
S: Longitudinal bed slope of the channel or the drain
Discharge equation (Q):
Q = A.V
A: Area of flow
V: Velocity of flow
Design of a drain using these equations is by 'trial and error'; a reasonable size of the drain or channel section is assumed, and the velocity of flow is checked with respect to the permissible value. If necessary, another trial is made with a revised value.
Highway Engineering

78. Sub-surface drainage
This aims at lowering the water table, controlling seepage for protecting the stability of the subgrade. Longitudinal and transverse drains are used for this purpose.
Subsurface drain to intercept seepage water Longitudinal and transverse drain system for less permeable soil
Design of filter
Perforated drain pipes may be used or graded filter material drains may be used.
The criteria for filter material design are permeability, piping and prevention of clogging.
Highway Engineering

79. Prevention of clogging:
The requirements are
Permeability ratio:
Piping ration:
Prevention of clogging:
(dp is the diameter of perforation in the drain pipe)
Cross drainage
Culverts (waterway less than 6 m)
Minor bridges (waterway 6 m to 30 m)
Medium-size bridges (waterway 30 m to 100 m)
Major bridges (waterway more than 100 m)
Causeways (allow water to flow over than for a short period at a time)
Highway Engineering

80. Chapter 9 Hill Roads and Special Roads
Highway Engineering

81. Class 5 (4.9 m wide- 1-t vehicles)
Hill roads, or ‘ghat’ roads, are those constructed in mountainous or steep terrain to connect places at significantly different elevations.
Border Roads Organisation has classified hill roads as Class-9 ( 6 m wide -3-t vehicles)
Class 5 (4.9 m wide- 1-t vehicles)
Class -3 (2.45 m to 3.65 m wide for jeeps)
Special aspects of hill roads
(a) Alignment
(b) Geometric design features
(c) Construction
(d) Drainage
(e Maintenance
Alignment
Obligatory points are based on strategic needs; Control points are governed by saddles, passes, crossings of water bodies and other natural features of the terrain.
'Resisting length' concept may be used as one of the criteria in assessing the suitability of alternative alignments. This is the effective length taking into account the total work done against the resistances to motion.
Highway Engineering

82. This criterion has to be used along with other requirements.
The route has to be necessarily much longer than the shortest distance in view of the high difference in elevation between the ends and limitations on gradients. Ineffective rises and falls are inevitable in such situations. The resisting length is obtained by adding to the actual length of the route, the product of ineffective rise and fall and the reciprocal of the coefficient of friction between the vehicle tyres and the pavement surface. For the alignment chosen, the resisting length should be a minimum.
This criterion has to be used along with other requirements.
Geometric design features
The Indian Roads congress code, IRC: (First Revision) , contains the information on the geometric design aspects of hill roads.
The standard values specified will be somewhat less than those for roads in normal terrain, depending upon the nature of the terrain and the classification of the road.
Design speeds are lower than normal, ranging from 20 to 50 km/h.
Highway Engineering

83. Minimum length of vertical curve is 15 m for speed up to 35 km/h.
Sight distance: Stopping sight distance is the absolute minimum required either on summits or horizontal curves for ensuring safety. For overtaking, double this is needed.
These values depend on the speed, ranging from 20 to 60 m for speeds from 20 to 50 km/h.
Minimum radii: For horizontal curves, minimum radii for hill roads vary with road classification and on whether it is mountainous terrain or steep terrain; it can range from 14 m to 50 m for the latter.
Transition curves: The length of transition depends on the speed and radius of the circular curve. For example, for a design speed of 20 km/h and for a curve radius of 15 m, the minimum length of transition is 30 m.
Gradients: For steep terrain, the ruling, limiting and exceptional gradients are 6%, 7% and 8% respectively.
Minimum length of vertical curve is 15 m for speed up to 35 km/h.
Hair-pin bends: They should be avoided or at least minimised as they constitute severe constraints on speeds, consistent with safety.
Highway Engineering

84. Structures required during construction: Revetments Retaining walls
Construction aspects
Structures required during construction:
Revetments
Retaining walls
Breast walls
Parapet walls
Tunnels(if inevitable)
Pavement surface: Bituminous surface with WBM base course is considered good for hill roads.
Drainage aspects of hill roads: Camber ranges from 1 in 50 to 1 in 33.
Side-drains are provided only on the hill-side; the size may be 0.60 m  0.45 m of triangular shape.
Catch-water drains: These are for intercepting surface-run-off, drain it parallel to the road and lead it into a cross-drainage structure such as a culvert.
Cross-drainage works: Culverts, causeways, and minor bridges are provided as frequently as is necessary.
Sub-surface drainage: This may be necessary if the depth to hard stratum is significant.
Longitudinal and/or cross drains may be provided.
Highway Engineering

85. Maintenance aspects of hill roads Maintenance of drainage structures
Prevention and correction of land slides
Clearance of snow in snow-bound areas and control of avalanches.
For prevention of landslides, provision of check walls and breast walls, grouting and rock bolting, turfing and growth of vegetation are practised.
Special Roads
(a) Expressways
(b) Urban Roads
Expressways: Superior highways meant for high-volume high-speed traffic.
Design speeds up to 120 km/h
Highway Engineering

86. Dual carriageways separated by a median Grade-separates crossings
Controlled access
Dual carriageways separated by a median
Grade-separates crossings
Superior pavements
Road-side amenities
Superior geometric design features
Road signals and markings
Roads in special locations:
Desert roads
Roads in water-logged areas
Roads in expansive clayey soils
Special treatment is needed for these.
Highway Engineering

87. Chapter 10 Highway Maintenance
Highway Engineering

88. Factors causing defects in highway pavements
(a) Deficiencies in subgrade preparation
(b) Deficiencies in the design and construction
(c) Traffic-related factors
(d) Deficiencies in the drainage arrangements
(e) Environmental factors
Defects in flexible pavements
(a) Ravelling-Progressive dislodging of aggregates
(b) Stripping-separation of bitumen coating and consequent loss of binding action
(c) Cracking-hair-line cracks at close intervals on the surface due to insufficient binder, and alligator cracking.
(d) Bleeding-due to excessive binder, collecting on the surface
(e) Pot-holes-due to localised failure of subgrade
(f) Wavy surface-undulations in the pavement surface with crests and troughs
(g) Rutting and corrugations-depressions and undulations in the longitudinal direction.
(h) Edge damage-irregular breakage at edges due to poor shoulder support
(i) Streaking in bituminous surface-presence of alternate lean and heavy lines of bitumen due to non-uniform application
Highway Engineering

89. Defects in rigid pavements
(a) Scaling of concrete-flakes coming off the surface due to improper mix design and excessive vibration during laying. Results in rough surface and poor riding quality
(b) Spalling of joints-faulty alignment of joint filler resulting in the chipping off of projections.
(c) Mud-pumping-soil slurry coming up through cracks due to settlement of subgrade
(d) Cracking-shrinkage cracks, warping cracks and structural cracks, the last type occur due to inadequate slab thickness for the traffic loads and repetitions.
Pavement evaluation
Assessing the condition of a pavement with respect to its structural adequacy and surface characteristics.
This helps in assessing maintenance needs and the need for providing overlays, if any.
Highway Engineering

90. Methods of evaluation
(a) Visual rating-by inspecting and assessing the magnitude and severity of various types of damage; there is subjective element in this approach and hence not popular.
(b) present serviceability index(PSI) approach-involves the measurement of deformation and extent of cracking; developed by the AASHTO. Equations for PSI were developed for both flexible and rigid pavements. The longitudinal profile is monitored by a Profilometer, developed by the AASHTO.
(c) Roughness Measurements approach-Roughness is a measure of pavement performance. Roughness measurements, obtained by a suitable device such as the 'Benkelman beam deflection device', form the basis of evaluating the pavement and for planning the necessary maintenance operations. This device is recommended by the IRC for the design of overlays for strengthening flexible pavements; this measures the response of a flexible pavements in terms of a surface rebound deflections under standard axle loading from a truck.
The standard wheel load is 4085 kg and tyre pressure is 5.6 kg/m2 [IRC: ]
Highway Engineering

91. Maintenance of highway pavements (a) Routine maintenance
Road inventorying
A systematic procedure of collecting the details of the existing condition of a pavement in service. This helps in assessing maintenance needs, as also in determining the need for overlay.
Maintenance of highway pavements
(a) Routine maintenance
(b) Periodic patch repair
(c) Special repairs such as provision of overlay
Maintenance of earth/gravel roads
Replenishing lost material
Grading and rolling
Maintenance of WBM roads:
Repairing ruts, pot-holes and other defects
Maintenance of bituminous roads:
Patch repair surface treatment
Resurfacing when needed.
Highway Engineering

92. Maintenance of cement concrete pavements:
Filling and treating cracks and joints
Replacing a slab when badly damaged by mud-pumping
Grouting, if considered suitable
Crack repair by special methods such as cross-stitching.
[Standards for road roughness were suggested for Indian roads by Kadiyali et al and adopted by IRC.]
Mechanised maintenance is faster with better quality control.
Strengthening of highway pavements
Flexible overlays
Rigid overlays
These can be provided either on flexible or rigid pavements for strengthening.
Flexible overlays: Benkleman beam deflection data provide the basis [IRC: ]
Highway Engineering

93. Rigid overlays for rigid pavements:
These may be fully bonded (monolithic), partially bonded, or unbounded with a separate layer, usually of bituminous material. [IRC: SP: ]
Rigid overlay over a badly damaged flexible pavement is called 'White-topping'. The design is based on the modulus of subgrade reaction of the existing pavement [IRC: ].
Design of rigid overlays
(a) Partially bonded overlays: The thickness of the overlay, h0 is given by
Here, hm = thickness of monolithic slab
he = thickness of existing concrete pavement
C = pavement condition factor
Slightly cracked  1.00
Fairly cracked  0.75
Moderately cracked  0.55
Badly cracked  0.35
Highway Engineering

94. Design of flexible overlays
(b) Unbonded overlays
(c) Fully bonded overlays: The thickness of the overlay is taken as the difference between the monolithic thickness of cements concrete pavement required for the present traffic and the existing thickness. [IRC: ]
Design of flexible overlays
Depends on intensity of rainfall and the traffic intensity/volume.
For example, for very heavy traffic (more than 1500 cupd) and medium rainfall intensity- 410 cm to 125 cm, 7.5 cm bituminous macadam.
Under 4 cm asphaltic concrete is considered to be adequate.
Highway Engineering

95. Chapter 11 Roadside Development and Arboriculture
Highway Engineering

96. Environmental impact of highways
Roadside development
The aim is to provide road-user amenities with minimal adverse impact on the landscape and environment.
Environmental impact of highways
(a) Alignment: Avoid disturbance to vegetative cover, natural drainage pattern and slope stability.
(b) Construction and maintenance operations:
Debris or waste material should be removed.
Natural watercourses to be protected from pollution.
Turfing of earthen shoulders as a protective cover.
Traffic control and regulation devices
Maintenance amenities
Road-user amenities
Traffic regulation, maintenance and road-user amenities should be provided in a well-planned manner for minimal impact on environment
Highway Engineering

97. (c) Deleterious effects on vehicular traffic Noise pollution
Air pollution
Degradation of aesthetics
Impact on the community in the vicinity
Efforts should be made to minimise the effects of these on the humans and the environment.
Roadside amenities
Rest areas
Service stations
Petrol bunks
Truck parks
Restaurants
Highway lighting
Landscaping
To conserve as also to enhance the natural beauty of the surroundings.
Highway Engineering

98. Treatment of intersections Roadside appurtenances
Factors that affect landscaping requirement of highways
Terrain
Type of road
Design speed
Climatic factors
Treatment of intersections
Roadside appurtenances
Conservation of existing features
Arboriculture
Roadside Arboriculture: Development of roadside plantation
Purposes:
Providing shade
Improving aesthetics
Screening of undesirable areas
Salubrious effects of vegetation
Preserving and enhancing nature and environment
Types:
Avenue planting
Group planting
Mixed planting
Highway Engineering

99. Flower plants and shrubs
Choice of plants should be appropriate to the locality and the climatic factors.
Highway lighting and illumination
For safe driving during nights, identifying roadside amenities and at special locations such as intersections, level crossings, temporary decisions, and so on.
Discerning an object/hazard on the highway and its vicinity:
Silhouette (Outline, profile or contour): Contrast with the background of a dark object.
Reverse silhouette: Contrast of an object brighter than the background.
Contrast of surface detail of the object
Definitions of terms related to highway lighting
Luminous flux: Radiant light given out by a light source
Lumen: Unit of luminous flux; it is the flux emitted in s solid angle of one steradian by a uniform point source of one candela.
Candela: Unit of luminous intensity; basic unit.
Highway Engineering

100. Lamp: A bulb or a light source
Luminance: Luminance intensity emitted/reflected per unit area of a surface (candela/m2).
Illumination: Luminous flux incident per unit area on a surface (unit is called 'lux' or lumen/m2)
Lamp: A bulb or a light source
Luminaire: A house for one or more lamps with a reflector
Lighting system: An array of luminaires having a characteristic light distribution.
Glare
Distribution of light from a luminaire may cause 'glare'
To reduce or avoid glare, vertical distribution such as cut-off and semi-cut-off types are used.
Horizontal distribution of light from a luminaire can be symmetrical, axial or non-axial. Each is useful in a particular set of conditions
Types of lamps for light distribution
Filament
Tubular fluorescent
Sodium vapour
Mercury vapour
Highway Engineering

101. Illumination required on a highway
I.S. Specifications are used in the design uniform lightning of the pavement is the aim.
(lux or lumen/m2)
Here lm = Lamp lumens
Cu = Coefficient of utilisation
LMF = Lamp maintenance factor (may be taken as 0.8)
S = Spacing between luminaires(m)
W = Width of roadway (m)
Cu is related to the ratio of width of area to mounting height of the luminaire (up to about 0.45)
Illumination of special locations
Intersections
Rotaries
Curves
Bridges
These require careful consideration of the factors involved in each case.
Highway Engineering

102. Chapter 12 Highway Economics, Finance and Administration
Highway Engineering

103. Benefits from a highway Primary or direct benefits
Highway Economics
Economic analysis and evaluation is important in the justification for a highway project.
A comparative economic study of different alternatives of either a new-project or an improvement of an existing road.
Benefits from a highway
Primary or direct benefits
Secondary or indirect benefits
Direct benefits: Reduction of operation and maintenance costs of vehicles, increase in revenue from vehicle taxes, income from transportation of persons and goods, reduction in accidents due to improvements, benefits to general public such as land appreciation , etc.
Indirect benefits: Increase in comfort and safety to the road-user, improved mobility of essential goods and services, role in defence and security, and increase in educational, business, health and recreational values.
Highway Engineering

104. Traffic-related factors – speed, traffic volume and nature of traffic
Total or economic cost of a highway
Initial cost of construction
Maintenance cost during design life
Vehicle operation cost
Design life
Cement concrete road  25 to 40 years
Asphaltic concrete  10 to 15 years
Waterbound macadam  4 to 8 years
Earth/gravel road  3 to 4 years
Vehicle operating Cost (VOC)
Factors affecting VOC
Road characteristics – surface roughness, type of surface, geometric features
Vehicle characteristics – age, make, engine capacity, load, fuel, and maintenance aspects
Traffic-related factors – speed, traffic volume and nature of traffic
Environmental factors – rainfall and temperature
Highway Engineering

105.  Nature of highway facility  Nature and characteristics of vehicles
IRC: SP: (Second Revision) contains the detailed procedure for computing VOC
Speed-flow equations: These equations characterise the effect of traffic on speeds; relate the speed V with traffic in PCU/h.
The variables are:
 Nature of terrain
 Nature of highway facility
 Nature and characteristics of vehicles
Sets of equations are developed for different vehicles moving on different highway facilities in different terrains.
VOC tables for individual components as well as for the entire cost are given based on the prices of April 1993; a multiplying factor based on whole-sale price index has to be used for future years.
Highway Engineering

106. Economic analysis/evaluation of highways
IRC: SP: 30(1993-First revision)
Highway project appraisal-consists of the study of costs and benefits to the road user.
Future needs of estimated traffic during design life are considered.
A comparison of benefits and costs is necessary to judge the economic viability of a project.
Different alternatives are studied and compared to choose the best option
Time-value for money:
Definitions:
Present worth: Present value of future payment or a series of such payments.
Discounting: The process of calculating the present worth of a future payment.
Discount rate: Interest rate at which future payments are reduced to common time.
Highway Engineering

107. Rate of return: rate at which economic benefits occur from a project.
Minimum attractive rate of return (MARR): This should be assumed appropriately to justify and implement a project.
Benefits to the user consist of VOL savings, travel-time savings, savings in accident costa and in maintenance cost.
Social benefits comprise those in agriculture, trade and commerce, and industry for benefit of the society.
Methods of economic evaluation
Net present value method (NPV)
Benefit /cost ratio method (B/C ratio)
Internal rate of return method (IRR)
All these are based on discounted cash flow-technique of discounting all future costs and benefits to a common year.
In the NPV method, the difference between benefits and costs should be positive for economic viability.
In the Benefit–Cost Ratio method, this ratio should be more than unity, for economic justification.
Highway Engineering

108. Average Annual Cost method
In the IRR method, the rate of return is more than that obtainable by investing the capital in the open market, the project is considered acceptable. These methods are illustrated in IRC: SP:
Average Annual Cost method
The alternative for which the average annual cost is the lowest is the most economical option.
The basis is the capital recovery formula of uniform series:
Annual cost,
Here, P: present capital
n: design life of the component in years
i: appropriate rate of interest for the component.
Highway Engineering

109. The two approaches are:
Highway financing
The two approaches are:
(a) Pay-as-you-go: Funds collected by the Government through taxes are spent on financing projects.
(b) Credit financing: Loans are raised from the public by the Government by issuing bonds, or from international lending agencies.
Sources of revenue: Taxes on fuel, vehicles and the road user, funds from central Road Fund (CRF), and toll revenue in the case of toll roads.
Public –Private-Partnership (PPP)
Several models are adopted for highway projects.
Ex: BOT –Build-Operate –Transfer
DBOT-Design-Build-Operate-Transfer
Highway Engineering

110. Highway Administration
Central Government is responsible for National Highways, along with National Highways Authority of India (NHAI).
Ministries of Defence, Railways, Rural Development take care of roads in special areas.
Research on Roads and Standards for Roads are taken care of by the Central Road Research Institute (CRRI) and the Indian Roads Congress (IRC).
State Governments are responsible for the maintenance of state Highways and District roads; Public Works Departments or the Roads and Buildings Departments are entrusted with the responsibility.
Road safety Audit is conducted by an independent team of experts.
Highway Engineering