---
title: "Highest and lowest points on vertical curves"
subject: "Transportation Engineering I"
chapter: 3
key: "semester_6/transportation_engineering_i:vc-highest-lowest-significance"
source: https://www.bctengineer.com/q/semester_6/transportation_engineering_i/vc-highest-lowest-significance
site: BCT Engineering
---

# Highest and lowest points on vertical curves

Transportation Engineering I · Chapter 3: Geometric Design of Highway

- Asked in: 2079 Chaitra, 2 marks
- Video: [Vertical Curve in Surveying/Highway Engineering | Formula Derivation + High & Low Points](https://www.youtube.com/watch?v=WQvvrnJNbdI) — CIVIL Solved
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/transportation_engineering_i/vc-highest-lowest-significance
- Whole chapter: https://www.bctengineer.com/md/semester_6/transportation_engineering_i/chapter-3

## Question

What is the significance of locating the highest and lowest points on vertical curves?

## Short answer

The highest point on a summit curve (zero gradient) gives maximum elevation for earthwork and setting out; drainage falls away from it. The lowest point on a valley curve (zero gradient) collects water, so drainage inlets are placed there with minimum gradient on both sides; its level checks bridge clearance and provides earthwork levels. Both points are needed for vertical alignment levels and longitudinal drainage design.

## Answer

- **Highest point of a summit curve** is the point of zero gradient on the curve. Its position and level give the **maximum elevation** of the road on the curve, which is needed for the earthwork levels and for setting out. Surface water drains away from it in both directions, so the side drains are graded away from this point.
- **Lowest point of a valley curve** is also a point of zero gradient, and **water collects** there. The drainage inlet, cross-drain or culvert is placed at this point, and a minimum gradient is ensured on both sides so that the water drains away. Its level is also used to check the clearance under bridges and to get the levels required for earthwork and setting out.
- In both cases, the position is required to calculate the vertical alignment levels and to provide proper longitudinal drainage.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. The highest point of a summit curve is the point where
   A. gradient is zero
   B. gradient is maximum
   C. the curve begins
   D. water collects
   Answer: A. It is the point of zero gradient, which fixes the maximum elevation, and drainage runs away in both directions. (Key point: Highest point on summit curve)

2. Why is the lowest point of a valley curve important for drainage?
   A. Water drains away fastest there
   B. Water collects there, so drain inlets or culverts are placed there
   C. It needs the steepest gradient
   D. It should be kept flat
   Answer: B. Water collects at the zero-gradient lowest point, so inlets are placed there and gradients on both sides must ensure it drains. (Key point: Lowest point on valley curve)

3. Locating these points is also required to
   A. calculate vertical alignment levels and provide proper longitudinal drainage
   B. decide the width of the carriageway
   C. set the superelevation
   D. find the traffic volume
   Answer: A. Their positions are needed for vertical alignment levels, earthwork and longitudinal drainage. (Key point: Use for levels)

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