The Longitudinal section drawing highway survey is a key task for civil engineers. In this article I explain how to prepare a longitudinal section drawing highway survey with clear steps. You will learn chainage level methods, gradient template use, and the curve template method with practical examples. This guide uses simple language and shows templates you can apply on site.
Why Longitudinal Section Matters
A longitudinal section shows the profile along the centerline of a road. It helps to design slopes, drainage, and earthworks. Before we dive into steps, here is a short overview of the main terms and tools.
Key Terms
Know these simple terms before drawing:
- Longitudinal section drawing — a side view of the road alignment.
- Chainage level — the distance along the road and the survey level at that point.
- Gradient template — a tool or guide used to set slopes and grade lines.
- Curve template method — used to lay vertical curves smoothly between gradients.
Tools You Need
Typical tools for a highway survey include:
- Dumpy level or total station
- Measuring tape or surveyor’s wheel (for chainage)
- Graph paper or CAD software for plotting
- Gradient template and vertical curve templates (physical or digital)
Step-by-Step: Chainage and Level Measurement
First, set up a clear process for measuring chainage level points. The steps below give a reliable workflow.
1. Set Reference and Datum
Choose a stable benchmark and datum. Record the benchmark elevation. This is the base for all chainage level readings.
2. Measure Chainage
Mark chainages along the centerline. Use regular intervals, for example every 20 m, 50 m, or 100 m. Note both the distance and the reference point name.
3. Take Levels
Use a level instrument to record reduced levels at each chainage. Repeat readings for accuracy. Enter values in a field book or spreadsheet.
4. Record and Check
Cross-check adjacent readings. Look for sudden errors or spikes. Correct any mistakes before plotting the profile.
Drawing the Longitudinal Section
Now convert chainage and level data into a clear longitudinal section drawing. Follow these plotting steps for both manual and CAD methods.
Plot Chainage vs Level
On graph paper or CAD, set horizontal scale for chainage and vertical scale for elevation. Plot each chainage point and connect them with a thin line to form the existing ground profile.
Add Proposed Road Levels
Mark the proposed levels along the alignment. Use your design grades to place these points. Draw a bold line for the finished road profile.
Using Gradient Templates and Curve Template Method
Gradient templates help apply consistent slopes. Vertical curve templates make transitions smooth. The method below is practical and easy to follow.
Apply Gradient Template
Choose the design gradient for each section. Use a template or calculator to plot grade lines. Templates can be physical rulers with slope markings or digital tools in CAD.
Use Curve Template Method for Vertical Curves
Where two gradients meet, insert a vertical curve. The curve template method uses simple calculations:
- Find the gradient change (g1 to g2).
- Choose a curve length based on design speed and comfort.
- Compute high or low point location and elevations at ends of the curve.
- Use the template to draw the parabolic curve between grades.
Practical Examples
Here are two compact examples to show the method in action.
Example 1: Short Road, Single Grade Change
Chainage 0 to 200 m. Existing levels measured every 20 m. Design: 0–100 m at +1%, 100–200 m at -0.5%. Use a 40 m vertical curve centered at chainage 100 m. Plot points and draw the curve using the gradient template method.
Example 2: Rolling Terrain with Multiple Curves
Longer route with several grade changes. Measure chainage level at 50 m spacing. Use gradient templates for each grade. Insert vertical curves where grades change. Check drainage by ensuring negative slopes near crossfall points.
Template Table and Quick Reference
Use this simple table to compare common template choices and their use.
| Template | Use |
| Gradient template | Plot consistent grade lines and cuts/fills |
| Vertical curve template | Draw smooth transitions between grades |
| Chainage tape or wheel | Measure distances along centerline |
| Level instrument | Record chainage level elevations |
Common Mistakes and Tips
Avoid these pitfalls during a longitudinal section drawing highway survey.
- Not checking benchmark stability — re-verify before starting.
- Using uneven chainage spacing — choose consistent intervals.
- Forgetting to adjust for instrument height — always record staff reading and instrument height.
- Skipping vertical curves — this creates poor road comfort and drainage issues.
- Not plotting both existing ground and proposed levels — you need both for earthwork estimates.
Frequently Asked Questions
What is chainage level in highway survey?
Chainage level is the distance along the road and the recorded elevation at that point. It shows where and how the ground stands along the alignment.
How do I choose gradient template values?
Choose gradients based on design speed, safety, and drainage. Use standard values from your local road design code and adjust for terrain.
When is the curve template method necessary?
Use the curve template method when two different gradients meet. It creates a smooth parabolic transition and improves ride comfort.
Can I draw longitudinal sections by hand?
Yes. Use graph paper, a scale, and templates. For more accuracy and repeatability, use CAD or spreadsheet tools.
Conclusion
Longitudinal section drawing highway survey work is steady but simple with the right steps. Measure chainage level carefully, apply gradient templates, and use the curve template method where needed. With practice, you will create clear profiles and better road designs.
