chapter 1 traffic characterstics

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Chapter-1 TRAFFIC CHARACTERISTICS

Prepared By: Ankit N Patel

Traffic Engineering

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What is TRANSPORTATIO

N?

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3 Transportation System

Definition of Transportation Modes A transportation system is an infrastructure that

serves to move people and goods efficiently. Efficient = safe, rapid, comfortable, convenient,

economical, environmentally compatible.

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4 Transportation SystemMajor transportation subsystems Land transportation: highway, rail Air transportation: domestic, international Water transportation: inland, coastal, ocean Pipelines: oil, gas, other

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5 Transportation

Movement of persons and goods over space

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6Study of Traffic Engineering

Traffic engineering is a comparatively new branch of engineering and has grown with the increase in traffic in recent years. As vehicular traffic began to increase, the congestion on the streets began to hamper the safe and efficient movement of traffic. More and more accidents were caused, and serious problems of parking and environmental pollution began to felt. It was therefore necessary to give increasing attention to the operational characteristics of highway transportation and study the need for better geometric design , capacity intersections traffic regulations, signals traffic signs, roadway markings, parking facilities and street lightning.

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7Introduction to Traffic

EngineeringTraffic EngineeringTraffic engineering is that branch of engineering which deals with

planning and geometric design of streets, highway, and operating traffic systems to achieve safe, economical, convenient and efficient movement of persons and goods.

Object of Traffic Engineering:The basic object of traffic engineering is to achieve efficient, free

and rapid flow of traffic with least number of traffic accident.Factors affecting Traffic:The Road userThe VehicleThe RoadwayThe environment

Drivers of various types of vehicles and pedestrians are known as road user. They are human being, hence affected by so many factors.

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8Traffic Characteristics

First of the most important scientific study is the study of the traffic characteristics. Traffic can be classified into two classes:Road Users.Vehicular traffic.Road user characteristicsHuman beings performing different roles in the traffic are most important elements of the traffic and so we have to study their characteristics and behavior. Various roles of human are such as driver, pedestrians, cyclists etc. The physical, mental and emotional characteristics of human beings affect their ability to operate motor vehicle safely or to service as a pedestrian. Hence it is important for a traffic engineer to study the characteristics and limitations of the road users.

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Roaduser Characteristics

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Traffic CharacteristicsThe various factors which affect road user characteristics may broadly be classified under four heads:PhysicalMentalPsychologicalEnvironmentalPhysical characteristics: The permanent physical characteristics of the driver are vision, hearing, strength and the general reaction to the traffic situations. Vision include the acuity of vision, peripheral vision and eye movement; glare vision, glare recovery and depth judgment. Field of accurate, clear vision is about a 3 degrees cone however the vision is fairly satisfactory up to 10 degrees in general and 20 degrees in horizontal plane. In vertical plane the vision may be limited to 2/3 of that in horizontal plane.Hearing is helpful for drivers but of more important for the pedestrians and cyclists.

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Mental Characteristics: Knowledge, skill, intelligence, experience and literacy can affect the road user characteristics. Knowledge of vehicle characteristics, traffic behavior, driving practice, rules of roads and psychology of road users will be quite useful for safe traffic operations. Psychological factors: These effect reaction to traffic situations of road users to a great extent. Attentiveness, anger, fear, anxiety, phobias, superstition, and impatience may effect the traffic performance to great extent. Environment factors: The various environmental conditions affecting the behavior of road user are traffic stream characteristics, facilities to the traffic, atmospheric conditions and locality. The traffic stream may consist of mixed traffic or heavy traffic whereas facilities to overtake to the faster vehicles may be limited. The behavior of the driver varies from one traffic stream to another. Similarly the facilities of the traffic separators, multi-lanes etc will effect the performance. Surrounding environment effect the performance of the traffic because one will get slower at the market places and will be faster at the open places.

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What is PIEv Theory ?Acc. To PIEV theory the total reaction time of the driver is

split into four parts .

Perception time

Intellection time

Emotion time

Volition time

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1) Perception time : It is the time required for the sensations received by the eyes

or ears to be transmitted to the brain through the nervous system .

2) Intellection time : It is the time required for understanding the situation.


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3) Emotion time : it is time elapsed during emotional sensations & Disturbance

such as fear , anger ,etc. with reference to the situation . 4) Volition time : volition time is the time taken for the final action. Total reaction time of driver may be vary from 0.5

sec to 4 sec

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Lag distance = v * t

Where, v = speed of vehicle in m/s t = total reaction time (s) [ as per IRC t = 2.5 s ]

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Lag distanceDefinition : The distance travelled by the vehicle during

the total reaction time is known as lag distance .

Reaction time of the driver is the time taken from the instant the object is visible to the driver to the instant the brakes are effectively applied.

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Vehicular Characteristics


Traffic Survey• It is quite important to study the various vehicular

characteristics which affect the design and traffic performance, because it is possible to design, a road for any vehicle but not for an indefinite vehicle. It will not be economically feasible to keep on increasing the geometric standards and thickness of pavement from time to time to meet the needs of a few vehicles whose weight and dimensions are increased.

• Traffic studies are carried out to analyse the traffic characteristics to decide geometric features and traffic control for safe and efficient movements.


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A knowledge of these characteristic is necessary for propergeometric design and traffic control systems allowing forsafe and smooth operations.– Static: include the weight and size of vehicles.– Dynamic: involve the forces that cause the motion of vehicle

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Static CharacteristicsDesign vehicle: the selected representative vehicle forthe geometric design and control systems– Its dimensions are important for the determination ofdesign standards for several physical components of thehighway:– lane width, shoulder width, parking bays length and width,and lengths of vertical curves.– Vehicle weight is important for the determination ofpavement depths and maximum grades.

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Dynamics characteristics of vehicles affecting road design are speed, acceleration and braking characteristics and some aspects of vehicle design. The speed and acceleration depends upon the power of the engine and the resistant to be overcome and are important in all geometric design elements.

The deceleration and braking characteristics guide safe vehicle operation. The stability of vehicle and its safe movement of horizontal curves are affected by the width of wheel base. The riding comfort on vertical curves depends on the design of suspension system of vehicles.

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Power of vehicle The power of the heaviest vehicles and their loaded weights

govern the permissible and limiting values of gradient on roads. From the total hauling capacity and power required to overcome the total tractive resistance it is possible to determine the speed and acceleration of the vehicle which in turn useful in traffic regulation, planning and design.

Braking characteristics The deceleration and braking characteristics of vehicles depend

on design and type of breaking system and its efficiency. The safety of vehicle operation, stopping distance, and the spacing between two consecutive vehicle in a traffic stream is affected by the braking capacity. Thus the highway capacity and overtaking sight distance requirements also get indirectly affected.

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THANK YOU

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