Question

A traffic survey conducted on a road indicated an average daily traffic count of 6000 vehicles. The axle load distribution on the same roads is given as under.

$\begin{array}{cc}\text{Axle load (tonnes)}& \text{Frequency of traffic (\%)}\\ 16-20& 20\\ 8-16& 50\\ 8& 30\end{array}$

The design period of stretch is 15 years, yearly traffic growth rate is 5%. The designed traffic (in million standard axle) for the above data is___.(Assume the standard axle load 8 tonnes)

Answer 1

$\begin{array}{ccc}\text{Axle load (t)}& \text{Mid value (t)}& \text{Frequency (\%)}\\ 16-20& 18& 20\\ 8-16& 12& 50\\ 8& 8& 30\end{array}$

$VDF=0.2{\left[\frac{18}{8}\right]}^4+0.5{\left[\frac{12}{8}\right]}^4+0.3{\left[\frac{8}{8}\right]}^4$
$=5.126+2.531+0.3=7.957$
$\text{Design traffic}=\frac{365A\left[\right(1+r{)}^n-1]VDF}{r}$
$=\frac{365\times 6000\left[\right(1+0.05{)}^{15}-1]\times 7.957}{0.05}\times {10}^{-6}msa$
$=376.02msa$