Introduction to Traffic Engineering | Transportation Engineering - Civil Engineering (CE) PDF Download

Traffic Engineering

Traffic engineering is that branch of engineering which deals with the improvement of traffic performance of road networks and terminals. This is achieved by systematic traffic studies, scientific analysis and engineering applications. 

1. Road User Characteristics

(a) Physical Characteristics:
Vision, hearing, strength and the general reaction to traffic situations.
The temporary physical characteristics of the road users affecting their efficiency are fatigue, alcohol or drugs and illness. All these reduce alertness and increase the reaction time and also affect the quality of judgment in some situations.

(b) Mental characteristics
Knowledge, skill, intelligence, experience etc. can affect the road user characteristics.

(c) Psychological factors:
Attentiveness , fear, anger, superstition, impatience, general attitude towards traffic and regulations

(d)  Environmental factors:
Traffic stream characteristics, facilities to the traffic, atmospheric conditions and the locality.

2.  Vehicular Characteristics (a) Static Characteristics

Static Characteristics of vehicles affecting road design are the dimensions, weight and maximum turning angle.

Maximum dimensions of road vehicles:
Maximum width of vehicles = 2.5 m
Maximum height (a) Single decked vehicle = 3.80 m (b) Double decked vehicle = 4.75 m Maximum Length (a) Single unit truck with two or more axles = 11.00 m (b) Single unit bus with two or more axles = 12.00 m (c) Semitrailer tractor combinations = 16.00 m (d) Tractor trailer combinations = 18.00 m

No combinations is allowed to be of more than two units and no such combinations, laden or unladen is allowed to have overall length exceeding 18 m.

Weight of Loaded Vehicles

Maximum weight of loaded vehicle affects the design of pavement thickness and gradients.
Limiting gradients are governed by both the weight and power of the heavy vehicles.

Power of Vehicles

• The power of the heaviest vehicles and their loaded weights govern the permissible and limiting gradient on roads.
• Height of the driver seat affects the clearance of the overhead structures. 
• The height of the driver seat affects the visibility distance.
• The length of vehicles affects the capacity, overtaking distance, and maneuverability of vehicles.
• The minimum turning radius depends on the length of the wheelbase and the features of the steering system and this affects the design of sharp curves for the maneuver of vehicles at slow speeds.

(b) Dynamic Characteristics

• The speed and acceleration depends upon the power of the engine and the resistances to be overcome.
• The stability of the vehicle and its safe movement on horizontal curves are affected by the width of the wheelbase and the height of center of gravity.
• Braking Test: Breaking test is conducted to measure the skid resistance of pavement surface.
• At least two the following three measurement are needed during braking tests in order to determine the skid resistance of the pavement:
  • Braking distance, L...................... (m)
  • Initial speed. u.............................. (m/s)
  • Actual duration of brake application, t(second)