Question

Write a paragraph describing the elements of traffic flow analysis and describe them by giving examples. State everything needed for traffic flow analysis and zoning

Answer 1

Some elements of traffic flow analysis are as follows :

1) Flow rate or volume - Number of vehicles passing a point during specific point of time is known as flow rate (q). It can be expressed mathematically as ,

q = N / T

where N = number of vehicles

T = observation period

For example - suppose 450 vehicles passes to point in 15 min, then flow rate is equal to

q = (450/15 ) x 60

= 3056 vehicle per hour

2) Speed - Distance traveled in a unit time is known as speed.It is given mathematically as,

s = distance traveled / time

For traffic flow analysis, time mean speed and space mean speed is useful

Time mean speed = arithmetic mean of speeds of different vehicles passing through a point within a given interval of time and given as,

S_t = 1/n S_i

where, n = number of measured vehicles

S_i = individual speed of vehicles

For example - suppose 20 vehicles were observed with 10 cars at 35kph, 8 cars at 40kph and 2 cars at 50kph then,

S_t = 1/20 [(10 x35) + (8 x40) + (2 x50)]

= 38.5 kph

Space mean speed - Rate of movement of traffic within a given section of road,

S_s = n/( 1/ n_i )

For example - For above question space mean speed is given by,

S_s = 20 / [(10/35) + (8/40) + (2/50)]

= 38.04 kph

3) Density - number of vehicles in given length of road at an instant point of time,

D= n/ L

For example - suppose 150 vehicle in 500m then density,

D = 150 / 0.5

= 300 vehicle per km

4) Spacing = Distance between two vehicles measured from front bumper of vehicle to that of another vehicle ,

Spacing = 1 / density

For example - For a road with density of 150 vehicle per km ,

spacing = 1 / (150/1000)

= 6.66 m

5) Traffic volume - Number of vehicles passing through a particular section in unit time at any selected period . It varies month to month, year to year hence several types of measurement of volume are used which will minimize these variations and are as follows

a) Annual average daily traffic (AADT) - total number of vehicles passing a site dived by 365

b) Annual average weekday traffic (AAWT) - Total weekday volume dived by 260

c) Average daily traffic - Average 24 hr traffic volume at a given location for a time less then a year .An ADT is valid only for a period over which it is measured

d) Average Weekday traffic Average 24 hr volume on weekdays at a given location for a time less then a year, such as a month or season