Module 2 : Traffic Measurement Procedures

Lecture 05 : Measurement at a Point

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Chandra's method

This method uses two factors: namely, velocity of vehicle type and its projected rectangular area to calculate the PCU value.

$$(PCU)_i = \frac{(V_c/V_i)}{(A_c/A_i)}$$ (1)

where $V_c$ and $V_i$ are mean speeds of car and vehicle of type i respectively and $A_c$ and $A_i$ are their respective projected rectangular area length * width on the road.

Table 1: Table for calculation using Chandra's method

Category	Vehicle	Dimension	Projected Area
Car	Car, Jeep, Van	3.72 x 1.44	5.39
Bus	Bus	10.10 x 2.43	24.74
Truck	Truck	7.50 x 2.35	17.62
LCV	Mini bus/trucks	6.10 x 2.10	12.81
M-Truck	Multi-axle truck	2.35 x 12.0	28.60
Bikes	Scooter, Motorbike	1.87 x 0.64	1.20
Cycle	Pedal Cycle	1.90 x 0.45	0.85
Autos	Auto, Tempo	3.20 x 1.40	4.48

Numerical Example

The table given shows the data obtained in spot speed study for various vehicle types. Find the PCU value for each vehicle type using the Chandra's Method.

Table 2: Table of spot speed study for various vehicle types

No	Car	3 wheeler	2 wheeler	LCV	HCV
1	11.32	8.67	6.67	6.0	7.4
2	6.74	7.25	8.27	6.88	6.09
3	11.11	9.68	7.75	7.5	5.88
4	6.67	6.98	6.12	8.57	6.38
5	8.11	8.77	9.52	9.67	5.66
6	7.41	8.77	11.9	8.57	5.66
7	8.11	9.52	6.97	5.7	5.55
8	9.93	9.40	6.97	4.68	6.12

Solution

Step 1 We have to find the space mean speed for each vehicle type using the formula:

$$V_s = \frac{n}{\Sigma_{i=1}^{n}(\frac{1}{v_i})}$$

Where n is the no. of observations and $v_i$ is the spot speeds.

Step 2 Find the PCU values using Chandra's Method. Use the table having the areas of various vehicle types given above.

Table 3: PCU values using Chandra's Method

No	Car	3 wheeler	2 wheeler	LCV	HCV
1	11.32	8.67	6.67	6.0	7.4
2	6.74	7.25	8.27	6.88	6.09
3	11.11	9.68	7.75	7.5	5.88
4	6.67	6.98	6.12	8.57	6.38
5	8.11	8.77	9.52	9.67	5.66
6	7.41	8.77	11.9	8.57	5.66
7	8.11	9.52	6.97	5.7	5.55
8	9.93	9.40	6.97	4.68	6.12
$v_s$	8.34	8.52	7.70	6.83	6.05

Then we can use the table given above to find the areas of different vehicle types to find corresponding PCU values.

Table 4: Table of PCU values

$v_s$	8.34	8.52	7.70	6.83	6.05
PCU	1	0.81	0.24	2.90	6.33