Transportation Engineering
Unit - 4
Traffic Studies
Traffic Sign and Signals Intersection Design
Topics:
Elements of Traffic Engineering and Traffic Control
Def: Traffic Engineering
• Traffic engineering is that branch of engineering which deals with planning and geometric design of streets, highway, abutting lands, and operating traffic systems to achieve safe, economical, convenient and efficient movement of persons and goods.
• Object of Traffic Engineering:
• To achieve free and rapid flow of traffic with least number of traffic accident.
• Factors affecting Traffic:
• The Roaduser
• The Vehicle
• The Roadway
• The environment
Drivers of various types of vehicles and pedestrians are known as road user.
They are human being, hence affected by so many factors.
Elements of Traffic Engineering and Traffic Control
Vehicles are classified as:
• Motorised
• Non-Motarised
• Vehicular characteristics
• The roadways type, riding quality, maintenance, surface, texture, light, reflection/ absorption, friction, drainage, weather resistance etc. are influencing the traffic.
• The environment considers for temperature, heat, cold, fog, mist, rainfall etc.
and their effects on traffic operation and human being.
Major Sections of Traffic Engineering
Elements of Traffic Engineering:
• Traffic characteristics
• Traffic studies and analysis- Traffic survey
• Traffic operation- Control and regulation-TCD
• Planning and analysis
• Geometric design
• Traffic Management and Administration
Traffic Characteristics
• Roaduser Characteristics
• Vehicular Characteristics
Roaduser Characteristics
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.
Major types of survey are as below:
Traffic Volume Study:
• Traffic volume is the number of vehicles crossing a section of road per unit time at any selected period. Traffic volume is used as a quantity measure of flow. The commonly used units are vehicles per day and vehicles per hour. A complete traffic volume study may include classified volume study by recording the volume of various types and classes of traffic.
The distribution by direction and turning movements and the distribution or different lanes per unit time.
• Different vehicles classes are converted to one common standard vehicle unit-PCU- Passenger Car Unit. Number of vehicles are multiplied by equivalency factor to convert number of vehicles into PCU.
Traffic Volume Study
Spot Speed Survey
• Spot speed survey is the instantaneous speed of a vehicle at a specified section or location.
Enoscope is the name of equipment use for this survey. Manually it is possible to measure the spot speed by entering the data into the record book.
The collected data are analysed and S-Curve is plotted. We can obtain medium speed, geometric design speed 85
thpercentile speed (Upper speed limit for regulation), 15
thpercentile speed, modal speed, space mean speed, time mean speed etc.
from collected data.
Spot Speed Survey
Speed and Delay Study
• Speed and delay studies give running speeds, overall speeds, fluctuations in speed and delay between two stations of a road spaced far apart.
They also give the information such as amount, location, duration, frequency and causes of the delay in the traffic stream. Various methods to carry out speed and delay survey are:
• Floating Car method
• Licence Plate record method
• By Interview
• By Photography and videography
Speed and Delay Study
Origin and Destination Survey
• The O and D studies of vehicular traffic determines their number, their origin and destination in each zone under study. The data of number of passengers in each vehicles, purpose of trip, intermediate stops made and reasons, actual direction of travel, selection of routes and length of trip etc.
also collected.
• Methods of O and D survey are:
• Road side interview method
• Licence plate method
• Return post card method
• Tag on car method
• Home interview method
Origin and Destination Survey
Traffic Flow Characteristics and Studies
• The measure of traffic flow are volume, density, and speed. The data for traffic volume, traffic density, space headway, time headway, features of road, traffic manoeuvres etc. are observed here. The basic traffic manoeuvres are diverging, merging, and crossing.
• Density is the number of vehicles occupying a unit length of lane of roadway at a given instant. It is expressed as vehicles per hour.
• The time interval between the passage of successive vehicles moving in the same lane and measured from head to head as they pass on the road is known as time headway.
• The distance between successive vehicles moving in the same line measured from head at any instance is known as space headway.
Traffic Flow Characteristics and
Studies
Traffic flow study is useful as following
• This is useful in geometric design features such as volume, number of lanes, width of carriageway etc.
• To decide traffic regulatory measures like one way movement.
• It is used in design of traffic control measures and devices.
• It is used for accident rate analysis and to determine measures to reduce and avoid accident.
• To decide speed trends and traffic patterns.
• To decide the priority for improvement and expansion.
• It is used for planning and control of existing facilities and routes.
• It is used for planning and designing the new facilities, To suggest improvement and expansion.
• It is used for planning of pedestrian facilities like sidewalks, crosswalks, subways and pedestrian signals.
• It is used for planning signal timing.
• It is used for structural design of pavement.
• To compute roadway capacity.
• To plan mass transit facilities.
Traffic Capacity Studies:
• Traffic Capacity Studies: Traffic Capacity is the ability of a roadway to accommodate traffic volume.
• C= 1000 V/ S
• V= Speed, KMPH
• S= Average centre to centre spacing of vehicles in m
• C= Capacity of a single lane vehicle per hr.
Traffic Capacity Studies
Parking Survey
• Parking survey is the work of data collection related to space available for parking of vehicles and number and type of vehicles demand for parking.
• Types of Parking
• Kerb parking
• Off street
• Kerb parking: vehicles are parked on the kerb or on the side of street or road.
• Types of Kerb Parking:
• Parallel Parking
• 30 0 angle parking
• 60 0angle parking
• 45 0 angle parking
• 90 0angle parking
• Angle parking is more convenient for the motorists than the parallel parking.
• Out of various angle parking, 45 0angle parking is the best and most convenient.
• Off street parking:
• When parking facility is provided at a separate place away from the kerb it is known as off-street parking.
• Types of offstreet parking:
• Surface parking lots
• Multi floor parking garages
Parking Survey
Accident Study
• Types of accident
• Minor injury
• Major injury
• Fatal
• Damage to property
• Accident reports are prepared in police station and town planning offices as
• Collision diagram
• Condition Diagram
• Preventive measures of accident are 3 E’s
• Engineering
• Enforcement
• Education
Traffic operations
• It is essential to impose adequate traffic regulations and traffic control devices for safe traffic operations.
• Traffic regulations should cover all aspects of vehicles, drivers, pedestrians, flow, accidents etc.
The traffic laws implemented by legislative laws are obligatory on all road users.
• (a) Traffic Regulation
• (b) Traffic Control Devices (TCD)
Traffic Regulation
• Various Traffic regulatory measures are:
• Issue driving licence- by checking age and conducting test drive
• Registration of Vehicles
• Transfer of Ownership
• Distinction between private and public vehicles
• Transport authorities
• Speed limit
• Limits of Weight
• Parking and halting Places
• Insurance fees
• Punishment of Violation and offences
• Provision of Control Devices
Traffic Control Devices
• The various aids and devices used to control, regulate and guide traffic is called TCD
• Signs
• Regulatory
• Warning
• Informatory
• Signals
• Fixed Time
• Manually Operated
• Traffic actuated
• Pedestrian
• Special Traffic
• Marking
• Pavement
• Kerb
• Object
• Reflector unit
• Delineators
• Islands
• Divisional
• Channelizing
• Pedestrian loading
• Rotary
• Lights
Traffic Signs
(A) Regulatory Signs:
• Regulatory Signs are meant to inform the road user of certain laws, regulations and prohibitions. The violation of these signs is a legal offence.
• Eg.
• Stop and give way sign
• Prohibitory signs
• No Parking signs
• Speed limit and vehicle control signs
• Restriction end sign
• Compulsory direction control and other signs
Regulatory Signs
Traffic Signs
(B) Warning Signs: warning or cautionary signs are
used to warn the road user of certain hazardous
conditions that exists on or adjacent to the
roadway. The warning signs are in the shape of a
equilateral triangle with its apex pointing
upwards. The warning signs are to be located at
sufficient distance in advance of the hazard
warned against; these distances are 120, 90, 60,
and 40 m respectively on NH/ SH , MDR, ODR,
and VR. On urban road the distance is 50 m
Warning Signs
Traffic Signs
Informatory Signs:
• These signs are used to guide the road user along routes, inform them of destination and provide with the information to make travel easier, safe and pleasant.
• Eg.
• Direction and place identification Sign
• Facilities Information Signs
• Other Useful information Signs
• Parking Signs
• Flood gauge
Informatory Signs
Informatory Signs
Traffic Signals
• At Intersection where a large number of crossing and
right turn traffic, there is possibility of collision and
accident. To provide orderly movement with safety
and speed, signals are provided at intersection. The
crossing streams of traffic flow are seperated by time
segeration
Traffic Signals
• Definition: Traffic Signals are control devices which could alternately direct the traffic to stop and proceed at intersections using red and green traffic light signals automatically.
• Advantages of Signals:
• Signal is provided at intersection to manage the traffic flow.
• Signals provide safety to vehicular traffic and pedestrian. They reduce and avoid the accidents.
• Signals are easy to understand compare to traffic police management at intersection.
Traffic Signals
Traffic Signals
• Disadvantages of Signals:
• Fast moving vehicles may cause rear end collision at signalised intersection
• Improper design of signal cycle length can cause fixed delay.
• Duration off-peak hour unnecessary delay occur at signalised intersection.
Traffic Signals
• Fixed Time Signals: are set to repeat regularly a cycle of red, amber and green lights. The timing demand to clear off the intersection with the help of detectors which are installed at the approaches. These are very costly.
• Pedestrian Signals: are meant to give the right of way to pedestrians to cross a road. The vehicular traffic should be stopped by red or stop signal on the traffic signal of the road.
• Traffic actuated Signals: are those in which the timings of the phase and cycle are changed according to traffic demand to clear off the intersection with the help of detectors which are installed at the approaches. They are very costly.
Road Marking
• Road marking are made of lines, patterns, words, symbols or reflectors on the pavement, kerb, sides of islands or on fixed object wiithin or near the roadway to control, warn, guide, or regulate the traffic. The marking are made by using white, black, yellow, colour paints.
Longitudinal lines are 10 cm thick and traverse lines
should be made in such a way that they are visible at
sufficient distance in advance. Yellow color marking are
used to indicate parking restrictions, continious centre
line and barrier line markings. Longitudinal solid lines
are used as guiding and regulating lines and are not
meant to be crossed by the driver. White color stop lines
are meant for vehicles to stop near the signalised section
and pedestrian crossing.
Road Markings
Center Lines
• On undivided two-way roads, the centre line separates the opposing streams of traffic and facilitates their movements.
• The centre line can be a single broken line, a
single continuous solid line (barrier line), a
double solid line or a combination of solid line
and broken line.
Types of lines used to mark lanes .
• The Divided Lines visible in the pictures above are called Lane Lines.
• Single and double solid lines, whether white or yellow, must not be crossed or even straddled.
• They should be treated as a wall on the road .
Double Lines.
• Single and double solid lines, whether white or yellow, must not be crossed or even straddled.
• Double Continuous lines are also used where visibility is restricted in both directions.
• Neither stream of traffic is allowed to cross the lines.
• The Double Continuous Lines can be both in WHITE or YELLOW
Combination Lines
• On a road with two centre lines, of which one is solid and the other broken, the solid line has significance only it it is on the left side of the combination as viewed by the driver.
• In such a case, the driver must be careful not to cross or straddle the centre line.
• If the line on your side is broken, you may cross or straddle it.
OverTake - but only if it is safe to do so.
• If the line on your side is continuous you must not cross or straddle it.
Stop Line.
• A stop line is a single solid transverse line painted before the intersecting edge of the road junction/ intersection.
• This line indicates where you are required to stop when directed by traffic officer, traffic light of stop sign.
• Where a pedestrian crossing is provided, the stop line is marked before the pedestrian crossing.
Give Way Line
• The give way line is usually a double dotted line marked transversely at junctions.
• These lines are generally supplemented by a reverse triangle give way sign painted on the road surface before the dotted lines or by a road sign installed beside the marking.
• Give way to traffic on the main approaching road.
Border Edge Line
• These are continuous lines at the edge of the
carriageway and mark the limits of the main
carriageway upto which a driver can safely venture.
Parking Prohibited Lines
• A solid continuous yellow line painted on the kerb or edge of the carriageway along with a "No-parking"
sign indicates the extent of no-parking area.
YELLOW BOX JUNCTION
• These are yellow crossed diagonal lines within the box.
• The vehicles should cross it only if they have a clear space available ahead of the yellow box.
• In this marked area vehicles must not stop even briefly.
Pedestrian Crossing
• These are alternate black and white stripes painted parallel to the road generally known as zebra crossing.
• Pedestrians must cross only at the point where these lines are provided and when the signal is in their favour at controlled crossings.
• You must stop and give way to pedestrians at these crossings.
• Pedestrian crossings are marked to facilitate and give the right of way to pedestrians.
Road Delinerators
• Are devices or treatment to outline the
roadway or portion there of to provide visual
assistance to drivers about the alignment of a
road ahead, especially at night.
Types of delineators are:
• Roadway indicators
• Hazard markers
• Object markers
Road Delinerators
Traffic Islands
• Are raised areas constructed within the roadway to establish physical channels through which the vehicular traffic may be guided.
• Types of Islands are:
• Divisional Islands: Divisional islands are dividing the highway in two one way roadways so that head on collision are eliminated and accidents are reduced.
• Channelizing Islands: Channelizing islands guide the traffic into proper channel through the intersection area.
• Pedestrian loading Islands: Pedestrian loading islands are provided at regular bus stops and similar places for the protection of passengers.
• Rotary Islands : Rotary islands is the large central island of a rotary intersection.
Needs of Islands
• Islands provide self controlled traffic. No need of traffic police to manage the traffic.
• Islands reduce conflicts points hence chances
of collision and accident also reduce.
Intersections
• Defintion: Intersection is the location of roadway where two or more approaches from different directions are meeting.
Intersection Types
At Grade Interchanges
(Grade Separated)
Channelized Unchannelized
