What are the Special Considerations for Hill Road Alignment? - VIVEK DHAKAL

## VIVEK DHAKAL

I'm a Civil Engineer. I usually write about engineering and some topical matters.

# What are the Special Considerations for Hill Road Alignment?

According to Nepal Rural Road Standards (2055), 2nd Revision 2071, the terrain is classified as Terai & Hills based on the topography of the country. The Terai covers the plain & rolling terrain having a cross slope of 0 to 25%. Hill covers the mountainous & steep terrain having a cross slope of 25 to 60% and more. The road passing through the hilly terrain with a cross slope of 25% or more is generally termed as Hill Road. A hill road usually consists of either a river route or a ridge route.

## What are the Factors Affecting the Alignment of Hill Roads?

There are various factors affecting road alignment. Moreover, there are some special considerations to be followed while selecting a hill road alignment. The major factors to be considered while deciding the alignment of hill roads are as follows:

### 1. Geological Stability

The road alignment should pass through a stable hill slope. The area should not be prone to erosion, landslides, rockfall, etc.

### 2. Availability of Construction Materials

Availability of construction materials near the construction site will reduce the transportation cost of materials thus making the project economical.

### 3. Cross Drainage Structures

Due to numerous watercourses present in the hilly regions, there may be the necessity of intense cross drainage works. The alignment should be so selected in such a way that the number of cross-drainage structures required becomes minimum.

### 4. Geological Structures

Excessive cutting of hard rock will be expensive. So, such areas should be avoided as much as possible from the road alignment.

### 5. Geometric Design

The alignment should be chosen to minimize the ineffective rise & fall, steep gradients, number of hairpin bends, etc. Also, the geometric design parameters should comply with the design guidelines & standards for hilly regions.

### 6. Altitude of the Road

• Rainfall (or Snowfall) ∝ Altitude
• Atmospheric Pressure ∝ $\frac{1}{Altitude}$
• As the altitude decreases, the number of cross drainage works required increases.

#### 1 comment

1. Hi, can u plz tell the location of road pic used