What is Highway Alignment?
The position or layout of the centerline of the highway on the ground is called highway alignment. The horizontal alignment includes the horizontal paths and horizontal curves vertical aluminum includes gradient and vertical curves.
The highway should align carefully as improper alignment should increase in
- Construction cost
- Maintenance cost
- Vertical operation cost
- Accident rates.
Ideal Requirement of Highway Alignment
Short: Alignment should be short. That is the minimum traveling distance.
Easy: The alignment should be easy to construct and maintain and easy for vehicle operation with easy curves and gradients.
Safe: Alignment should be safe for construction and maintenance. It should be safe for traffic operation with a geometric design.
Economic: Alignment could be considered economical only if the total cost including initial cost maintenance cost and vehicle operating cost is the lowest.
Factor Controlling Highway Alignment
- Geometric consideration
- Obligatory points
- Traffic considerate
- Economic considerate
- Other considerate.
Obligatory Point
This is a survey point where the road is passed. These points should be decided whether the highway is pass or not. I have covered which cases obligatory points should pass the road or which is not.
Points through which highway Alignment should pass:
- Along with hilly areas.
- Corresponding to the proper location of the bridge.
- Connect the intermediate city.
- Connect industrial area.
- Ignoring the middle ground.
Points through which highway should not pass.
- Submerged area Swampy land.
- Places of historical and archaeological importance.
- Restricted Area for Defense National Security.
- A densely populated area.
- Expensive structural element.
Horizontal Alignment and gradient
The alignment curve should be as flat as possible. It helps to drive safely and improve road performance. So that the gradient is also designed flat as possible. do not heavy rise gradient or fall gradient.
Type of Traffic
The type of traffic can also affect highway alignment. Different types of traffic moving on the road. So we should design for different types of vehicles.
If the fast-moving vehicle, alignment should be designed straight with using the minimum curve as possible.
If possible highway alignment should be separate for the fast-moving vehicle.
Volume of Traffic
We study traffic volume, how it grows each year, and when it’s busiest. Using all this information, we make the final decision on the design of the road.
Traffic volume is also the main factor to affects road alignment.
We should design of road carrying at least 20 years of traffic volume moving on the road.
The new road should align keeping in view the desired line, traffic flow pattern, and future trends.
Geometric design such as the gradient radius of the curve, and sight distance also governs the final alignment of the highway.
Economy: B/C>1
In working out the economics the initial cost of maintenance and vehicle operation cost should be taken into account.
Earthwork and Backfilling
The initial cost can decrease if high embankment and deep cutting are avoided and the alignment is chosen in a manner to balances the cutting and filling.
Land leveling through earthworks and backfilling after land acquisition can be expensive. We adjust alignment as needed to avoid excessive excavation and backfilling, which helps control costs.
Horizontal Curve Radius
Highways with big curves are not ideal. To ensure a smooth and steady speed on highways, the turns in the road should have a radius of less than 230 meters. To meet this standard, the road alignment can be adjusted.
Railway Crossing
Ideally, roads should cross railway tracks at a 90-degree angle. For high-speed lanes, national highways, or expressways, it’s recommended to build a bridge over the railroad tracks to prevent traffic congestion.
Proper Drainage
Proper water drainage is very necessary in the road alignment. Without a drainage system on the highway that is an uncompleted highway alignment design. In the monsoon heavy rain occurs. if you don’t provide drainage in the alignment, the road is defective, and water pond issues.
Mainly the edge of the road is provided for water drainage.
Engineering Survey for Highway Alignment
In this survey, the different methods include. Which will be discussed in these articles.
- Map study
- Reconnaissance
- Preliminary Survey
- Final Location and details survey
These are the methods for highway alignment surveys. Which method is important in the highway alignment selection?
Map Study
If the topographic map is available, it is possible to fix the routes of the road.
The main feature like rivers, hills, valleys, etc. is also shown on their map.
By the study of such maps, it is possible to have an idea of several possible alternate routes so that further details of these may be studied later on site. The possible different alignments can be selected on the topo map.
- Alignment avoiding valley pond or lake.
- When the road has to cross a row of hills possible the cross through a mountain pass.
- Approximate location of bridge site for crossing rivers avoiding bends of rivers if any.
- In the map study, the alternate routes of the road can be fixed. It gives rough guidance of the routes to be further surveyed in the field.
Recent
- All the possible details that are not available in the map study are collected and noted down.
- The details collected are below:
- Valley, ponds, marshy land, and other permanent structures along the route are not available on the map.
- Approximate values of the gradient, length of the gradient, and curve radius of alignment.
- No and type of cross drainage structure, maximum flood level groundwater level.
- Soil type along the alignment.
- Source of construction material, water, and location of stone quarries.
- As a result of the reconnaissance survey, a few alternative alignments may be chosen for future study.
Preliminary survey
A preliminary survey is an initial study or investigation conducted to collect important information about a specific area. It should be taken before detailed planning or construction begins.
It helps in understanding the feasibility, potential challenges, and overall conditions of the site, guiding the subsequent stages of planning and development.
The main objective of the preliminary survey
- To collect the necessary physical information and details of topography drainage and soil of various alternative alignments.
- Compare different proposals because of the requirement of good alignment.
- Estimate the quantity of earthwork and work out the cost of alternate alignment.
- Finalize the best alignment from all the considerations.
- The survey was carried out by the following method.
