Traffic Engineering
Traffic Engineering

Traffic Engineering 1. Traffic Characteristics, 2. Traffic Studies and Analysis, 3. Traffic Control Regulation.

1. Traffic CharacteristicsA. Road User Characteristics – Vision. B. Vehicular Characteristics – Dimension, Weight of Loaded Vehicle, Power of Vehicle, Speed of Vehicle. C. Breaking Characteristics – Retardation, Skid Distance, Skid Resistance, Breaking Efficiency.

2. Traffic Studies and AnalysisA. Traffic Volume Study, B. Traffic Speed Studies, C. Traffic Flow Characteristics & Capacity Study, D. Origin and Destination (O & D) Study, E. Parking Study, F. Accident Studies.

A. Traffic Volume Study –  Traffic Volume (q), PCU (Passenger Car Unit), Measurements of Traffic Volume- Manual Method,  Mechanical Method. Presentation Of Traffic Volume Data- Annual Average Daily Traffic (AADT), Annual, Average Hourly Traffic (AAHT), Annual Average Week Day Traffic (AAWT), Average Daily Traffic (ADT), Trend Chart, 30th Highest Hourly Volume, Volume Flow Diagram at Intersection, Variation Chart, Periodic Volume Count – 1.Hourly Expansion Factor (HEF), 2.Daily Expansion Factor (DEF), 3.Monthly Expansion Factor (MEF). Peak Hour Factor (PHF).

B. Traffic Speed Studies- Types of Speed- Spot Speed, Average Speed- Time Mean Speed, Space Mean Speed, Journey Speed, Running Speed, Generally there are two type of speed studies carried out- 1. Spot Speed Study- Representation Of Spot Speed Data-  Speed Distribution Table, Frequency Distribution Curve- Model Speed. Cumulative Speed of Vehicle- 98th percentile speed, 85th percentile speed, 15th Percentile Speed, 50th percentile speed. 2. Speed And Delay Study- Floating Car Method, Derivation Of Floating Car Method.

C. Traffic Flow Characteristics & Capacity Study 1. Traffic Capacity Studies- Traffic Volume, Traffic Density (K), Jam Density (Kj), Space Headway (S), Time Headway (HT), Traffic Capacity, Basic Capacity, Practical capacity, Calculation of Theoretical Maximum CapacityMax Theoretical Capacity from Space Headway, Max Theoretical Capacity from Time Headway. 2. Traffic Flow Characteristics Studies- Macroscopic Characteristics: Green Shield’s Stream Model, Microscopic Characteristics. Delay & Queue Analysis at Signalized IntersectionDelay (D), Queue (Q).

D. Origin and Destination (O & D) StudyMethod for Origin and Destination data calculation: Road Side Interview Method, License Plat Method, Tag On Car Method, Return Post Card Method, Home Interview Method. Representation of Origin and Destination DataO&D Table, Desire Lines, Pie Chart.

 E. Accident StudyMathematical Analysis of Accident Studies, Accident Case StudyWhen A Moving Vehicle Collides With Parked Vehicle.

 F. Parking Study  Off Street Parking, On Street/ Kerb Parking – Parallel Parking, Angle Parking30° Angle Parking, 45° Angle Parking, 60° Angle Parking, 90° Angle Parking. Parking statistics – Parking Accumulation, Parking Volume, Parking load, Average Parking Duration, Parking Turnover, Parking Index.

3. Traffic Control Devices & Regulation – A. Intersection, B. Traffic Signals, C. Traffic Sign, D. Road Marking.

A. Intersection- 1. Intersection at Grade- Requirements of Intersection at Grade, Type of Intersection at GradeUnchannelized Intersections, Channelized Intersections, Rotary Intersection. Design Factors For Rotary Intersection- Design Speed, Shape of Rotary Island, Radius of Curve at Entry, Radius of Curve at Exit, Radius of Central  Island, Width of Carriageway At Exit & Entry, Width of non-weaving section, Width & Length of Weaving Section, Length of Weaving Section, Capacity Of Rotary. 2. Grade Separated Intersection – Trumpet interchange, Diamond interchange, Full Cloverleaf interchange, Partial Cloverleaf interchange. Advantages of Grade Separation, Disadvantages of Grade Separation.

B. Traffic SignalsType of Traffic Signals – Traffic Control Signals (Fixed-time Signal, Traffic Actuated (automatic) Signal, Manually Operated Signal), Pedestrian Signal, Special Traffic Signal. Type of Co-ordination of Traffic Signal System- Simultaneous System, Alternate System, Simple Progressive System, Flexible Progressive System. Important Terminology of Traffic Signals  Cycle, Cycle Length (C), Interval, Green Time, Red Time, Amber Time, Phase, Lost Time (tL)Startup Lost Time (tSL) Clearance Lost Time (tCL), Effective Green Time (gi), Lane Capacity. Method of Signal Designing- Webster Method.

C. Traffic Sign: Classification of Signs – Regulatory / Mandatory Signs, Warning/ Cautionary Sings, Informatory Sign.

D. Road MarkingFunctions of Road Markings. Types of Road Marking – Pavement Marking (Centre Lines, Lane Line, Edge Lines, No Passing Zone Marking, Turn Markings, Stop Line, Crosswalk Lines, Bus Stops), Kerb Marking, Object Marking, Reflector unit marking. Road Delineators.


In traffic control devices & regulation, we detailed discussed about traffic sign & road marking but remain topics are discussed in other post.

Traffic studies or surveys are carried out to analyze the traffic characteristics. These studies help in deciding the geometric design feature and traffic control for safe and efficient traffic movements. The traffic surveys for collecting traffic data are also called traffic census. The various traffic studies generally carried out are: Traffic Volume Study, Traffic Speed Studies.

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