1. TRAFFIC SURVEYS & STUDIES AND THEIR IMPLICATION ON DESIGN OF ROADS
ER NIROJ KUMAR DASH

2. DEFINITION
Traffic Engineering is defined as that phase of highway engineering which deals with the planning and design of highways and abutting lands, with the traffic operations thereon for the safe, convenient and economic transportation of persons and goods.

3. INTRODUCTION
Traffic Engineering deals with the improvement of traffic performance of road networks and terminals.
Includes planning geometric design on one hand and regulation and control on the other.
Therefore, deals with the application of scientific principles, tools, techniques and findings for safe, rapid, convenient and economic movement of people and goods.

4. SCOPE OF TRAFFIC ENGINEERING
Basic object is to achieve efficient, free and rapid flow of traffic with least number of accidents.
Scope covered by following categories :
Traffic Characteristics
Traffic Studies and analysis
Traffic Operations
Traffic Planning
Geometric Design
Administration and Management

5. Traffic Studies For establishment and updating design standards
A detailed knowledge of the operating characteristics of the traffic is essential to form a basis for the establishment of traffic control or for design of streets and highways. The results of data collected are used in :
Traffic planning
Traffic management
Economic studies
Traffic and environmental control
Monitoring trends
For establishment and updating design standards

6. Traffic Studies ( Contd.)
Surveys carried out to analyse the traffic characteristics.
Helps in deciding the geometric design feature and traffic control for safe and efficient movement.
Traffic studies can be broadly divided into two categories :
Concerned with characteristics of traffic in transit
Those related to land use movements

7. Traffic studies in transit
Traffic volume studies
Speed and delay studies
Origin – Destination studies
Traffic flow
Traffic capacity
Road life studies
Motor vehicle use studies
Land use movement studies :
Parking studies
Accident studies

8. Volume Studies
Quantity of movement per unit time at a specified location
Time period depends on the purpose of study
Useful to establish :
Relative importance of any route
Fluctuations in flows
Distribution of traffic on the road system
Trends in the road use & economic computations
Capacity requirements and geometric design
Classified volume for design of roads & terminals
Structural design

9. Methods of traffic volume studies
Manual counting
Automatic recorders or counters
Permanent counting recorder
Magnetic detectors
Pressure sensitive detectors
Electronic detectors
Portable recorders
Moving car method of counting

10. Schedule of volume counts
Traffic census : Count of traffic is basically required for improvement to existing roads. Points to be noted for traffic counts on non-urban roads :
Should be done twice a year, once during peak season of harvesting and marketing and the other during off-season.
Counts be made round the clock for seven consecutive days.
A road should be divided into convenient sections each carrying similar traffic (approx).

11. Census sites should be well away from urbanised developments and villages.
A day may be divided into 3 shifts of 8 hours each.
Recording should be done for each direction of travel separately.
Traffic should be recorded by making tally marks in five dash system in hourly column.
Highest peak hour traffic in a day for fast and slow vehicles be highlighted in red.
Traffic volumes be expressed in numbers by vehicle type.

12. ADT (Average Daily Traffic) used for :
Planning major streets
Improvement, construction/reconstruction of road
Computing accident rates
Computing highway user revenue
Classified volumes used for :
Geometric and structural design of roads
Computing capacities/ highway user revenue
Hourly volumes used for :
Deficiency in capacities, geometric design
Determine number and width of lanes
Parking demands
Planning traffic control
Location of interchanges

13. Equivalency(PCU) factors for various types of vehicles on rural roads
Vehicle type
Equivalency factor
Motor cycle/Scooter
Passenger car/Pick-up/Auto
Agricultural tractor/LCV
Truck/Bus
Truck- trailer /Tractor trailer
Cycle
Cycle rickshaw
Hand cart
Horse drawn vehicle
Bullock cart

14. Equivalency(PCU) factors for various types of vehicles on urban roads
Vehicle type
Equivalency factor
(% of vehicle type in traffic )
Motor cycle/Scooter
Passenger car/Pick-up van
Auto-rickshaw
Light commercial vehicle
Truck/Bus
Agricultural tractor- trailer
Cycle
Cycle rickshaw
Horse drawn vehicle
Hand cart
5% 10% & above

15. Capacity of different types of roads.
Types of roads Capacity PCU/day. (both direction) Single lane with earthen shoulder 1000 Single lane with hard shoulder 2500 Intermediate lane with earthen shoulder 5000 Two lane with earthen shoulder Four lanes divided carriageway (Depending on access control)

16. Uses of Road inventory
Basis of more extensive surveys like road use studies, traffic studies, sufficiency rating.
Special studies can be done quickly as all data are readily available.
Maps used to establish new business centres, service routes etc.
For planning by State Government.
For planning by Central Government.
For marking speed zones.

17. Purposes of spot speed studies
Spot speed is the instantaneous speed of a vehicle at any specified time. Purposes are :
Planning traffic control- establish speed zones, traffic signals, locating warning, regulatory & information signs, non passing zones etc.
Speed trends
Accident studies- analysis and remedies
Capacity studies
Geometric design

18. Location for spot speed studies
At all major highways
At all high accident frequency points
Where installations of traffic signals and stop signs are contemplated
Representative locations for collecting basic data for future planning
Time of study- One hour each between 9 am to 12 am, 3 pm to 6 pm, 6 pm to 10 pm.

19. Delay studies
Difference in running speed and journey speed is due to delay in the traffic.
These studies are for following purposes : provides facts on amount, location, delay. Helps in remedy to congestion situation.
Helps in getting sufficiency rating.
Traffic assignment for new facility.
Economic studies
Efficiency of roadway
Changes in traffic control- parking prohibition, signal time revision, new one way street.
Show cost to community of an inadequate road.

20. Origin-Destination study
Provides information about travel desire and helpful in identifying efficient transportation system. The information needed as :
Where the people want to go
How they travel-auto, bus, truck etc.
When they travel-time, direction etc.
Why they travel-purpose of trip
Where they stop- for parking demands

21. Method of making O-D Survey
Drivers’ interview
Parker Survey.
Post card Survey.
Home interview method.
Licence place method.
Cards through school children method.

22. Specific uses of O-D survey
Planning major street systems, freeway locations, location of interchanges.
Improving present facilities of existing street systems.
Designating of one way street, Limited parking, Traffic signals.
Planning and designing futures facilities.

23. Parking studies. Purpose of parking studies :
To determine congestion in city or town area.
To asses the suppressed parking demand.
The capacity of the existing parking facilities.
To estimate the demands of public for parking.
To decide the capacity, location and type of future parking facilities.

24. Parking surveys Inventory studies:
Inventories of available facilities such as kerb spaces, parking lots, parking garages, space not used for parking, time restriction and tabulation.
Cordon count i.e. Counting all cars and other vehicles entering and leaving the area hourly.
Direct interview i.e. About origin, destination and purpose of parking.
Patrol survey i.e. touring small sections of areas at suitable intervals and counting numbers of vehicles parked.

25. Customer interview method:
Land use method:
Demand is determined by the studies of co-relations between sales and parking areas required for monetary unit of sale which depend on type of business, city and cost of living.
Co-relating floor area and store area of a commercial establishment.
Customer interview method:
Customer are interview while entering commercial stores, restaurants, hotels, cinemas, offices and other places of work. The suppressed demand of parking can be established from the difference between the desired and present users.

26. Analysis of presentation of data
The information collected is analysed and presented under following heads:
Total immediate demand.
Deficiency or excess of parking spaces.
Origin destination of parking volume.
Turn over of parking spaces.
Limited parking i.e. time restrictions.
Use of loading zones and taxi stands.
Distance walked by various groups.
Purpose of the parker.
Estimated demand, if parking space is available.

27. Accident studies.
This study includes the factors which contribute to road accidents and effective measures to reduce the occurrence of accidents. The traffic engineer makes an important contribution to better design and control of the road system. Four major factors involved in accidents are:
The vehicle.
The road and its condition.
The road users.
The environment.

28. Accident surveys. Macro surveys: Micro surveys:
Provides information on categories of road users with vehicle and location sub divided by times, types and manoeuvres.
Micro surveys:
This enables particular danger points in the road system to be identified and causes evaluated the locations are referred to as Black Spots and require a detailed study.

29. Measures for preventing accidents
Effective measures for improving safety and preventing accidents can be divided in to three main groups:
Engineering.
Enforcement.
Education.
Engineering measures:
Road design: Segregation of traffic, lighting system, white line markings, alignment, road surface, road margins, warning and control devices, drainage.
Design and maintenance of vehicles.
Enforcement measures:
Speed control, traffic control devices, training and supervisions, medical check etc.

30. Traffic control devices.
Used to control, regulate and guide traffic.
Requirements – Attention, meaning, time for response and respect of road users.
Common devices – Signs, signals, markings, islands, lighting.
Traffic signs – Regulatory/warning/informatory.
Regulatory or Mandatory – Inform users of laws, regulations, prohibitions.
Warning signs - Warn the road users of hazardous conditions existing on the road way.
Informatory signs - Guide road users along the routes, inform destination and distance to make travel easier safe and pleasant.

31. Cautionary Signs

32. Mandatory Signs

33. Informatory Signs

34. Mandatory Signs

35. GEOMETRIC DESIGN STANDARDS
Elements of geometric design:
Dimensions and weight of road vehicles.
Terrain classification and design speed.
Design of road cross section: width of carriageway, width of roadway, shoulders, median strips, side slopes, cambers, land width, building lines and control lines.
Super elevation.
Curves – Horizontal and vertical
Sight distance.
Gradients.
Alignment – horizontal, vertical, lateral and vertical clearances at under passes.

36. Highway Cross-section Elements
Traffic separators or medians:
-to prevent head-on collision
-channelize traffic into streams at intersections
-shadow crossing and turning traffic
-segregate slow traffic & protect pedestrians
Kerbs
Road Margins
-Shoulders, parking lanes, Lay-byes, Bus-bays, Frontage Roads, Drive ways, Cycle tracks, Footpath or side walks, Guard rails, Embankment slopes

37. GEOMETRIC DESIGN STANDARDS
Elements of geometric design:
Dimensions and weight of road vehicles.
Terrain classification and design speed.
Design of road cross section: width of carriageway, width of roadway, shoulders, median strips, side slopes, cambers, land width, building lines and control lines.
Super elevation.
Curves – Horizontal and vertical
Sight distance.
Gradients.
Alignment – horizontal, vertical, lateral and vertical clearances at under passes.

38. Terrain classification (As per IRC)
Terrain classification Per cent cross slope of the country. Plain 0-10 Rolling >10-25 Mountainous >25-60 Steep >60

39. DESIGN SPEEDS km/h Road class Plain Rolling Mountainous Steep NH&SH
Ruling
Minimum
MDR
Ruling
Minimum
ODR
Ruling
Minimum VR
Ruling
Minimum

40. WIDTH IN PLAIN FOR NH & SH
Sl. No.
Item
Plain & Rolling Terrain
Mountainous & Steep terrain
Open areas
Built-up areas 1.
Land width (metre)
Normal 45 30 24 20
Range
30-60 2.
Building line
(Overall width), metre 80
Distance between building line and road boundary should be 3-6 metres 3.
Control line (Overall width), metre.
150 4.
Roadway width metres
Single lane 12
6.25
Two lane
8.8

41. Recommended standards for building and control lines
Sl.No.
Road classification
Plain & Rolling Terrain
Mountainous & Steep Terrain
Open areas
Built-up areas 1 2 3 4 5 6 1.
NH & SH 80
150
3-6
3-5 2.
MDR 50
100 3.
ODR
25/30 35 4. VR 25 30

42. WIDTH OF ROADWAY IN PLAIN AND ROLLING TERRAIN
Sl. No.
Road Classification
Road width (m) 1.
NH & SH (Single & two lanes)
12.00 2.
MDR (Single & two lanes)
9.00 3.
ODR
Single lane
7.50
Two lane
9.0 4.
VR (Single lane)
7.5
WIDTH OF ROADWAY IN MOUNTAINOUS AND STEEP TERRAIN
NH & SH (Single lanes)
6.25
NH & SH (Two lanes
8.80
MDR and ODR (Single lane)
4.75
4.00

43. WIDTH OF CARRIAGEWAY Sl. No. Description Width (M) 1 Single lane 3.752.
Intermediate
5.50 3.
Two lane without raised kerbs
7.0 4.
Two lane with raised kerbs
7.5 5.
Multi lane width per lane
3.5
Note: On village roads the width of single lane may be restricted to 3.0 metres.

44. EXTRA WIDTH OF PAVEMENT ON HORIZANTAL CURVES
Radius of curves (m)
Extra width (m)
Single lane
Two lanes
Up to 20
0.9
1.5
21-40
0.6
41-60
1.2
61-100
Nil
Above 300
PAVEMENT CROSS FALL / CAMBER
Sl. No.
Surface type
Camber/ Cross fall (%) 1.
High type BT or CC
1.7 – 2.0 2.
Thin BT
2.0 – 2.5 3.
WBM, Gravel 4.
Earth
3.0 – 4.0

45. SIGHT DISTANCE, RADIUS OF HORIZANTAL CURVES
Speed Km/h
Sight distance, metre
Radius of horizontal curve (m)
Stopping
Intermediate
Overtaking
Plain & Rolling Terrain
Hilly
Not affected by snow
Snow bound 20 40 - 14 15 25 50 23 30 60 33 35 80 45 90
165
120
235 65
180
340
155
240
470
230
100
360
640
Note: 1. Values table are minimum. Use higher values where feasible.
2. Stopping sight distance is absolute minimum for design.

46. MAXIM GRADE CHANGE NOT REQUIRING A VERTICAL CUVES
GRADIENTS
Sl No.
Terrain
Gradient (%)
Ruling
Limiting
Exceptional 1.
Plain / Rolling
3.3 5
6.7 2.
Mountainous & Steep Terrains of elevation up to 300 m. above MSL 6 7 3.
Steep terrain of elevation more than 300 m. above MSL 8
MAXIM GRADE CHANGE NOT REQUIRING A VERTICAL CUVES
Sl. No.
Design speed( Km/h)
Max. grade change % not requiring vertical curve.
Up to 35
1.5 40
1.2 15
1.0 4. 65
0.8 5. 80
0.6 6.
100
0.5

47. MINIMUM LENGTH OF VERTICAL CURVES
Sl. No.
Design speed
Minimum length of vertical curve (m). 1.
Up to 35 15 2. 40 20 3. 50 30 4. 65 5. 80 6.
100 60

48. MINIMUM RADII OF SUMMIT CURVES FOR VARIOUS SPEEDS
Speed Km/h. 25 30 35 40 50 60 65 80
100
Minimum Radius, m 95
130
170
250
380
440
670
1045

49. Example of Flexible Pavement Design related to traffic data
Based on IRC :37 – 2012 (Tentative Guidelines for the Design of Flexible Pavements)
Information needed in estimating design traffic :
Initial traffic after construction in terms of number of commercial vehicles per day (CVPD).
Traffic growth rate during the design life in percentage.
Design life in number of years.
Spectrum of axle loads.
Vehicle Damage Factor (VDF).
Distribution of commercial traffic over the carriageway.
Only the Commercial Vehicles having gross weight of 30 KN or more considered.

50. Assessment of the present day average traffic should be based on seven-day -24-hour count made in accordance with IRC:
Traffic growth rate
Present day traffic has to be projected for the end of design life at growth rate ‘r’ estimated by studying and analysing the past trends of growth and demand elasticity of traffic with respect to macro economic parameters
If data for annual growth rate of commercial vehicles is not available or if it is less than 5%, a growth rate of 5% should be used(IRC:SP )

51. Design life- Should be designed for a minimum period of 15 years for NH & SH. For other roads a design life of 10 to 15 years adopted.
Vehicle Damage Factor – VDF is a multiplier to convert the number of commercial vehicles of different axle loads and axle configuration into number of repetitions of standard axle load of magnitude 80 KN i.e. Equivalent number of standard axles per commercial vehicles.
VDF should be arrived at carefully by carrying out specific axle load surveys on the existing roads.

52. Where sufficient information on axle loads is not available and the small size project does not warrant any axle load survey, VDF may be used from the table below :
Initial traffic volume Terrain
in terms of CVPD Rolling/Plain Hilly
More than

53. Distribution of commercial traffic over the carriageway :
Single lane roads – Design based on total number of CVPD in both directions.
Two lane single carriageway – 50% of total number of CVPD in both directions.
Four lane single carriageway – 40% of total number of CVPD in both directions.
Dual carriageway roads
Dual two lane c/w roads- 75% of CVPD in each direction
Dual three lane c/w roads – 60% of CVPD
Dual four lane c/w roads – 45% of CVPD

62. LIST OF PUBLICATIONS OF IRC RELATED TO TRAFFIC
IRC : Traffic census on non urban roads.
IRC : Code of practice for road marking.
IRC : Guidelines on design of horizontal curves for highways and design tables.
IRC : 52 – 2001 Recommendation about the alignment survey and geometric design of hill roads.
IRC : 54 – 1974 Lateral and vertical clearance at under passes for vehicular traffic.
IRC : 62 – 1976 Guide lines for control of access on highways.
IRC : 64 – 1990 Guide lines for capacity of roads in rural areas.
IRC : 65 – 1976 Recommended practice for traffic rotaries.
IRC : 66 – 1976 Recommended practice for sight distances on rural highways.
IRC : 67 – 1977 Code of practice for road signs.
IRC : 73 – 1980 Geometric design standard for rural highway.
IRC : 93 – 1985 Guide lines on design and installation of road traffic signals.
IRC : 106 – 1990 Guide lines for capacity of urban road in plain areas.

63. Grade Separated Intersection

64. Grade Separator

65. Roundabout

66. Signalised Intersection

67. T-Junction

68. Y-Junction

69. Channelized Intersection

70. THANK YOU