![Scope of traffic engg.
Traffic characteristics:-improvement of traffic
facilities( vehicle , human[road user])
Traffic studies and analysis
Traffic operation-control and regulation:-laws of
speed limit, installation of traffic control device
Planning and analysis
Geometric design:-Horizontal and vertical curve
design
Administration and management:-‘3E’concept](https://image.slidesharecdn.com/unit3-170607063846/85/Unit-3-3-320.jpg)
Unit 3
- 1. By- MD MOZAFFAR MASUD Assistant Professor Department of Civil Engineering JIT, JETGI, Barabanki
- 2. 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 professional practice of planning, designing and operating traffic systems to achieve safe and efficient movement of persons and goods. Objective of traffic engineering: Achieve efficient ‘free and rapid’ flow of traffic Reduce the no. of accidents. Various phases of traffic engineering are: (3Es) Engineering (constructive i.e. geometric design of road) Enforcement (traffic laws, regulation and control) Education (publicity and through school and television)
- 3. Scope of traffic engg. Traffic characteristics:-improvement of traffic facilities( vehicle , human[road user]) Traffic studies and analysis Traffic operation-control and regulation:-laws of speed limit, installation of traffic control device Planning and analysis Geometric design:-Horizontal and vertical curve design Administration and management:-‘3E’concept
- 4. Traffic characteristics Road user characteristics Physical Mental Psychological Environmental Vehicular characteristics Vehicle dimension Weight of loaded vehicle Power of vehicle Speed of vehicle Braking characteristics
- 5. Traffic studies Traffic studies are carried out to analyze the traffic characteristics. These studies helps in deciding the geometric design features traffic control for save and efficient traffic movement. The various traffic survey studies generally carried out are: Traffic volume study Speed study Spot speed study Speed and delay study Origin and destination study Traffic flow characteristics Traffic capacity study Parking study Accident studies
- 6. Traffic volume study It is the number of vehicles crossing a section of road per unit time at any selected period. It is used as a quantity measure of flow: the commonly units are vehicles/day or vehicles/hour The objects and the used of traffic volume study are: It is generally accepted as a true measure of the relative importance of roads and in deciding the priority for improvement and expansion. It is used in planning, traffic operation and control of existing facilities and also for planning the new facilities. It is used in the analysis of traffic patterns and trends.
- 7. Traffic volume study Useful in structural design of pavement Used in planning one-way streets and other regulatory measure. Turning movement study used in the design of intersections, in planning signal timings, channelization and control devices. Pedestrian traffic volume study is used for planning side walk, cross walks, subway and pedestrian signals.
- 8. Counting of traffic volume Mechanical count These may be fixed type or portable type, it is automatically record the total number of vehicle crossing a section of the road in a desired period. Other methods of working the mechanical detectors are by videos, radar detector. Advantage is that it can work throughout the day and night for the desired period. Manual count It is possible to obtain data which can not be collected by mechanical counter such as vehicle classification, turning movement.
- 9. Presentation of traffic volume data Average annual flow: (veh/year) Annual average daily traffic (AADT or ADT): Average daily traffic (ADT) represents the total traffic for a year divided by 365, or the average traffic volume perday. (veh/day) Hourly average traffic: (veh/hr) •Thirtieth highest hourly volume or the design hourly volume is found from the plot between hourly volume and the number of hours in a year that the traffic volume is exceeded. The 30th highest hourly volume is the hourly volume that will be exceeded only 29times in a year and all other hourly volumes of the years will be less than this volume. The 30th highest traffic volume is found to be satisfactory from both facility and economic considerations.
- 10. SPEED STUDY Spot speed:- it is the instantaneous speed of a vehicle at a specified location. Average speed:- it is the average of spot speed of all vehicles passing at given points on the highway. Space mean speed:- (harmonic mean)Average speed of vehicles in a certain road length at a given instant.
- 11. Time mean speed:-(arithmetic mean) Mean speed of vehicle at a point in space over a period of time or It is the average of instantaneous speeds of observed vehicles at the spot. Running speed:- it is the average speed maintained by a vehicle over a particular stretch of road, while the vehicle is in motion ; this is obtained by dividing the distance covered by the time during which the vehicle is actually in motion. Journey speed or travel speed:- it is the effective speed with which a vehicle traverse a particulars route between two terminals, it includes delay and stoppages. Where, Vt= time mean speed n= no. of vehicles V= speed of the vehicle
- 12. Types of speed study 1.Spot speed study 2.Speed and delay study Use of spot speed study To use in planning traffic control and in traffic regulation. To use in geometric design for redesigning the existing highway. To use in accident studies. To study the traffic capacity.
- 13. Speed and delay study The speed and delay studies give the running speeds, overall speeds, fluctuations in speeds and the delay between two stations of a road. It gives the information such as the amount, location, duration and cause of delay in the traffic stream. The result of the spot and delay studies are useful in detecting the spot of congestion. The delay or time lost traffic during the travel period may be either due to fixed delays or operational delays. Fixed delay occurs primarily at intersections due to traffic signals and at level crossings. Operational delays are caused by the interference of traffic movement, such as turning vehicles, parking vehicles, pedestrians ..etc.
- 14. Presentation of spot speed data A graph is plotted with the average value of each speed group on X-axis and the cumulative percent of vehicles travelled at or below the different speeds on Y-axis. From the graph(i.e. Cumulative frequency distribution curve) followings can be obtained. 98thpercentile speed-Design speed 85thpercentile speed-Maximum speed 50thpercentile speed-Median speed 15thpercentile speed-Minimum speed Modal average speed(frequency distribution curve): A frequency curve of spot speed is plotted with average value of each speed group of vehicle in X-axis and the percentage of vehicle in that group on the Y-axis. The speed corresponding to peak value of curve is denoted as modal speed
- 15. Methods of speed and delay study Floating car or riding check method License plate or vehicle number method Interview method Elevated observations Photographic technique
- 16. Floating car or riding check method In the floating car method a test vehicle is driven over a given course of travel at approximately the average speed of the stream, thus trying to float with the traffic stream. A number of test runs are made along the study stretch and a group of observers record the various details. One observer is seated in the floating car with two stop watches. One of the stop watch is used to record the time at various control point like intersections, bridges or any other fixed points in each trip. The other stop watch is used to find the duration of the individual delays. The time, location and cause of these delays are recorded by the second observer. The number of vehicle overtaking the test vehicle and the overtaken by the test vehicle are noted in each trip by third observer. The no. of vehicles travelling in the opposite direction in each trip is noted by fourth observer. In this method the detailed information is obtained concerning all phases of speed and delay including location, duration and causes of delay.
- 17. Floating car or riding check method where, t⁻= average journey time in minute q= flow of vehicle(average volume) in one direction of the stream na = average number of vehicles counted in the direction of the Stream when the test vehicle travels in the opposite directions ny= the average no. of vehicles overtaking the test vehicle minus the no. of vehicles overtaken when the test is in the direction of ‘q’ Tw= average journey time, in minute when the test vehicle is travelling with the stream ‘q’ Ta= average journey time, in minute when test vehicle is running against the stream ‘q’
- 18. The consolidated data collected from speed and delay studies by floating car method on a stretch of urban road of length 3.5 km, running North-South are given below. Determine the average values of volume journey speed and running speed of the traffic stream along either direction. Example-1
- 20. Origin and destination studies The object of this study is Plan the road network and other facilities for vehicular traffic Plan the schedule of different modes of transportation for the trip demand of commuters. It gives the information like the actual direction of travel, selection of routes and length of trip. Used in planning new highway facilities and in improving some of the existing system. To plan the transportation system and mass transit facilities in cities including route and schedules of operation To locate expressway or major routes along the desire lines. To locate terminals and to plan terminal facilities. To locate new bridge as per traffic demands. To locate intermediate stops of public transport.
- 21. Methods of ‘O’ and ‘D’ survey Road-side interview method License plate method Return post card method Tag-on-car method Home interview method
- 22. Traffic flow characteristics and studies The basic traffic maneuvers are diverging, merging, crossing and weaving. Traffic Flow(q):-the rate at which vehicles pass at a fix point (vehicles per hour)= N(3600/t). Traffic Density(k):-no. of vehicles(N) over a stretch of roadway(L) i.e. vehicles per kilometer = N/L Time headway:-Time interval between the passage of the fronts of the successive vehicles at a specified point. Average time headway= average travel time per unit distance x average space headway
- 23. Space headway:-distance between front of successive vehicles. Average space headway= space mean speed x average time headway Flow Density Relationship Flow= density x space mean speed q= K x V Density = 1/ space headway 1/hs Space mean speed = flow x Space headway q x hs Density = flow x time per unit distance K = q x t
- 24. Traffic capacity studies Traffic capacity: The ability of a roadway to accommodate traffic volume. It is expressed as the maximum number of vehicle in a lane or a road that can pass a given point in unit time, usually an hour. Volume represent an actual rate of flow where as capacity indicates a maximum rate of flow with a certain level of service. Basic capacity: It is the maximum no. of passenger car that can be pass a given point on a roadway during one hour under the most nearly ideal roadway and traffic conditions. It is otherwise known as theoretical capacity.
- 25. Possible capacity: It is the maximum no. vehicle that can pass a given point on a roadway during one hour under prevailing roadway and traffic conditions. Practical capacity: It is the maximum no. of vehicle that can pass a given point on a roadway during one hour, without traffic density being so great as to cause unreasonable delay, hazard or restriction to the driver freedom to maneuver under the prevailing roadway and traffic conditions. C= 1000 V/S S= average spacing of vehicle in m, C is the capacity in vehicle per hour per lane.
- 26. Peak-Hour Factor It is basically represent the variation in traffic flow with in an hour. Observations of traffic flow consistently indicate that the flow rates are found in the peak. A 15 minute period within an hour is not sustained through out the entire period and that is why we need to use the peak-hour factor. Normally on freeways the peak-hour factor values range from 0.80 to 0.95.
- 27. Passenger Car Unit (PCU) The different vehicle classes have a wide range of statics characteristics and dynamic characteristics, apart from these the driver behavior of the different vehicle classes is also found to vary considerable. Therefore mixed traffic flow characteristics are very much complex when compare to homogeneous traffic and it is difficult to estimate the traffic volume, capacity of roadway under the mixed traffic flow, unless the different vehicle classes are converted to one common standard vehicle unit. Therefore it is a common practice to consider the passenger car as the standard vehicle unit to convert the other vehicle classes and this unit is called passenger car unit.
- 28. PCU value depends upon the several factors, such as: Vehicle characteristics Transverse and longitudinal gaps or clearance between moving vehicles. Speed distribution of the mixed traffic stream, volume to capacity ratio. Roadway characteristics. Regulation and control of traffic. Environmental and climatic conditions.
- 29. Passenger car equivalency factor(PCU) As per IRC:86-1983
- 30. Traffic Capacity Maximum flow occurs when the speed is Vsf/2 and the density is Kj/2 Where, Kj= jam density= 1000/spacing of vehicle Vsf= free mean speed K= q/v q= average volume of vehicle, (veh./hr) V= space mean speed of vehicle,kmph
- 31. Level of service(LOS) It is define as a qualitative measure describing the operational condition within a traffic stream, and their perception by motorist and passengers. Or Rating of acceptable level of congestion LOS definitions A: Free flow, low traffic, high speed B:Stable flow, noticeable traffic C:Stable flow, traffic interactions, D:Unstable flow, High density, movement restrictions E:Unstable flow, lower speed, volume is nearly equal to capacity, little freedom F:Unstable flow, no freedom, traffic volume can drop to zero, stop & go
- 36. Traffic operations Number of conflicts at intersection Crossing conflicts Merging conflicts Diverging conflicts