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Module 3: Geometric design of highways

Lecture 16 Horizontal alignment III

For single lane:

$\displaystyle m_1$	$\textstyle =$	$\displaystyle R-R\cos(\alpha/2)$
$\displaystyle m_2$	$\textstyle =$	$\displaystyle \frac{(S-L_c)}{2}\sin(\alpha/2)$

**Figure 1:** Set back for single lane roads ()
$\begin{figure}\centerline{\epsfig{file=../../../figeps/g15-setback-distance-single-lane,width=8cm}}\end{figure}$

The set back is the sum of

and

given by:

$\begin{displaymath} m=R-R\cos(\alpha/2)+\frac{(S-L_c)}{2}\sin(\alpha/2) \end{displaymath}$

(1)

where $\frac{\alpha}{2}=\frac{180L_c}{2\pi R}$ . For multi-lane road $\frac{\alpha}{2}=\frac{180L_c}{2\pi (R-d)}$ , and

is given by

$\begin{displaymath} m=R-(R-d)\cos(\alpha/2)+\frac{(S-L_c)}{2}\sin(\alpha/2) \end{displaymath}$

(2)