The basic objective of traffic engineering is to achieve a free & rapid flow of traffic with the least no. of accidents. For these various studies are carried out. These studies are divided into-
- Traffic Characteristics
- Traffic studies and Analysis
- Traffic Control Regulation
Study of traffic characteristics is the most important, for any improvement of traffic facilities.
In traffic characteristics, we generally study
- Road user characteristics
- Vehicular characteristics
- Breaking characteristics
Road user Characteristics
It is important to study the characteristics and limitations of road users because the physical, mental and emotional characteristics of human beings affect their ability.
Factors affecting road user characteristics are-
Vision, hearing, strength and General reaction to traffic situations.
Knowledge, skill, intelligence, experience, and literacy
Attentiveness, fear, anger, superstitions, impatience, general attitude towards traffic and regulations and maturity.
Facilities to the traffic, atmospheric condition, and locality.
The study of vehicular characteristics affects the design and traffic performance.
Vehicle dimensions mainly considered are the overall width, height, and length of different vehicles, particularly of the largest ones.
The width of the vehicle affects the width of the traffic lanes, shoulders and parking facilities.
Height of the vehicle affects the clearance to be provided under structures such as overbridges, underbridges, electric, and other service lines.
Length of the vehicle is an important factor in the design of horizontal alignment as it effects the extra width of pavement and minimum turning radius. Length affects the safe overtaking distance, capacity of a road and parking facilities.
Weight of Loaded Vehicle
The maximum weight of loaded vehicle affects the design of pavement thickness and gradients. In fact, the limiting gradients are governed by both the weight and power of the heavy vehicles.
Power of vehicle
The power of the heavy vehicles and their loaded weights decides the permissible and limiting values of gradients on roads. The total resistance to traction consisting of inertia, rolling resistance, air resistance, and grade resistance.
Speed of Vehicle
Vehicle speed affects-
- Sight distance
- Super elevations, length of transition curve and limiting radius on horizontal curves
- Length of transition curves on vertical valley curve and on bumps
- Width of pavement and shoulder on straight and on horizontal curves
- Design gradient
- Capacity of traffic lane
- Design and control measures on intersections
Deceleration and breaking characteristics of vehicles depend on the design and type of braking system and its efficiency.
The safety of vehicle operation, stopping distance and spacing between the two consecutive vehicles in a traffic stream are affected by the braking capacity.
At least two of the following three measurements are needed during the braking tests in order to determine the skid resistance of the pavement-
- Braking distance (L meter)
- Initial speed (u m/sec)
- Actual duration of brake application (t sec)
Thus, if initial velocity and breaking length is known, ‘t’ can be calculated.
After the application of breaks, the work done against the frictional force for stopping the vehicle will be equal to the kinetic energy of the vehicle.
L= Braking distance
g= Acceleration due to gravity
f= coefficient of friction
u= initial speed of vehicle
breaking efficiency= (f obtained from breaking test/fmax known)
Joints are too important for the rigid pavements because the joints are responsible for reducing stresses developed due to temperature variations. There are two type of joints-
- Longitudinal Joints
- Transverse Joints
The Transverse joints are subdivided into three categories-
- Expansion Joints
- Contraction Joints
- Construction Joints
Rigid Pavements are those which possess noteworthy flexural strength or flexural rigidity. The rigid pavements are generally made of Portland Cement Concrete (CC) and are therefore called ‘CC Pavements’. Plain cement concrete pavements slabs made of specified strength characteristics are laid, with or without steel reinforcement at the joints.
Flexible Pavements are those which on the whole have low or negligible flexural strength and are rather flexible in their structural action under the loads. Means, Flexible pavements are designed to pass the load immediately from the point where it occurs.