Question

A traffic survey conducted on a road yielded an average daily traffic count of 5000 vehicles. The axle load distribution on the same road is given in the following table

$\begin{array}{cc}\text{Axle Load}& \text{Frequency of}\\ \text{(tonnes)}& \text{Traffic(\%)}\\ 18& 10\\ 14& 20\\ 10& 35\\ 8& 15\\ 6& 20\end{array}$

The design period of the road is 15 years. The yearly traffic growth rate is 7.5%. The load safety factor (LSF) is 1.3. If the vehicle damage factor (VDF) is calculated from the above data, the design traffic (in million standard axle load, msa)is____

• A. 309

Answer 1

The correct option is A 309
Calculation of vehicle damage factor:

$\text{VDF}=\frac{V_1{\left(\frac{W_1}{W_s}\right)}^4+V_2{\left(\frac{W_2}{W_s}\right)}^4+V_3{\left(\frac{W_3}{W_s}\right)}^4+V_4{\left(\frac{W_4}{W_s}\right)}^4+V_5{\left(\frac{W_5}{W_s}\right)}^4}{V_1+V_2+V_3+V_4+V_5}$

Where,
$W_s=\text{standard axle load}=80kN=8.2tonnes$

$\text{VDF}=\frac{10{\left(\frac{18}{8.2}\right)}^4+20{\left(\frac{14}{8.2}\right)}^4+35{\left(\frac{10}{8.2}\right)}^4+15{\left(\frac{8}{8.2}\right)}^4+20{\left(\frac{6}{8.2}\right)}^4}{10+20+35+15+20}$

$=4.988$

$\Rightarrow N=\frac{365\times 5000\left[\right(1.075{)}^{15}-1]}{0.075\times {10}^{-6}}\times 4.988\times 1.3$

$=309msa$