Traffic Engineering

The basic objective of traffic engineering is to achieve free & rapid flow of traffic with least no of accidents. For this various studies are carried out. These studies are divided into

1. Traffic Characteristics

2. Traffic Studies and Analysis

3. Traffic Control Regulation

---

  Traffic Characteristics  

In traffic characteristics, we generally study

1. Road User Characteristics
2. Vehicular Characteristics
3. Breaking Characteristics

A. Road User Characteristics

Factor affecting Road User Characteristics:

1. Physical: Vision, hearing, strength and General reaction to traffic situation.
2. Mental: Knowledge, skill, experience, intelligence.
3. Psychological: Fear, anger, impatience, maturity.
4. Environmental: Facilities to the traffic, atmospheric condition and locality.

Vision

\(vision = \frac{x}{y}= \frac{\text{Actual distance}}{\text{Requried distance}}\)

 

6/6 Vision / Normal Vision: It is an ability of a person to recognize a letter of size 8.5 mm at a distance of 6m.

6/9 Vision / Poor Vision: This vision is poorer then normal vision because he can recognize at a distance of 6 m but a Normal person can recognize at a distance of 9 m.

NOTE: Concept of 6/6 and 6/9 vision used to design of location of sign board.

B. Vehicular Characteristics

In vehicular characteristics, we generally study

1. Dimension
2. Weight of Loaded Vehicle
3. Power of Vehicle
4. Speed of Vehicle

Dimension

• Length of vehicle affects turning radius, extra widening, parking design etc. (Maximum length 18 meter)
• Width of vehicle affects lane width, shoulder width and parking design.  (Maximum width 2.44 meter)
• Height of vehicle affects height of bridges, height of pole, etc. (Maximum height 4.75 meter)

Weight of Loaded Vehicle

Weight affects design gradient & thickness of pavement.

Power of Vehicle

It affects limiting & design value of gradient.

Speed of Vehicle

It affect all geometrical element & traffic control devices.

C. Breaking Characteristics

At least two of the following three parameters are needed during the breaking test in order to determine skid resistance of pavement.

• initial speed (u m/s)
• length of skid distance (L meter)
• Time of break application (t sec)

⇒ Retardation 

v-u = at

(v=o)

-u= at

-a= u/t

Retardation =\(\frac{\text{initial speed}}{\text{time}}\) 

⇒ Skid Distance

\(L=ut+\frac{1}{2}at^{2}\).

\(a=\frac{-u}{t}\).

\(L=ut+\frac{1}{2}\frac{-u\cdot t^{2}}{t}\).

\(L=ut-\frac{1}{2}ut\).

\(L=\frac{1}{2}ut\).

\(\text{Skid distance} = \frac{1}{2}\times \text{initial speed}\times \text{time}\).

⇒ Skid Resistance

v² = u² +2aL (v=0)

u²= -2aL

\({L=\frac{u^{2}}{-2a}}\)…..(i)

Δ KE = workdone

\(-\frac{1}{2}mu^{2}=-m\cdot g\cdot f\cdot L\).

\(L=\frac{u^{2}}{2gf}\)…..(ii)

from eq  i & ii.

(-a)= gf

\(f=\frac{-a}{g}\).

\(\text{Skid Resistance} = \frac{\text{Retardation}}{\text{accelaration due to gravity}}\)

⇒ Breaking Efficiency

\(\eta _B= (\frac{f_\text{obtained}}{f_\text{max}}\times 100)\).

\(f_\text{obtained} =\frac{u^{2}}{2gL}\)

 

---