Longitudinal Section (L Section of Road) and Cross Section of Road

December 6, 2022

Have you ever wondered what lies beneath the asphalt of your local roadways? If so, you’re in luck! In this blog post, we’ll look at the longitudinal section and cross-section of roads that make up a road, as well as some of the key features you’ll find in each element. So, pull up a chair and get comfortable—it’s time to take a closer look at the roads!

Longitudinal section of Road 

A longitudinal section view of a road shows the direction of travel and its elevation. This section can be useful for determining the inclination, or slope, while passing from one point to another. The longitudinal section also allows you to determine if the existing road is in good condition or if any improvement is needed.

This information is then used to design and build roads and to plan for maintenance and repair. It even shows the different pavement layers of the road, from surface to sub-base. During geometric design, the longitudinal section displays horizontal and vertical curve details.

What is a cross-section?

Cross section of road is a term used to describe the shape and dimensions of a road when viewed from the front. It typically includes the width of the roadway, the height or slope of the sides, and presence of elements such as retaining walls, drains etc. .

The cross-section of a road plays a vital role during the designing and construction phase. For example, a road with very steep side slopes may be more challenging. The typical cross section of road could help to know the toe point based on side slope and other alternatives such as to provide retaining wall or other retaining structures could be explored. Best part is implications of these changes in quantities of different construction materials can be instantly known. Ultimately, the cross-section of a road is an essential factor to consider when designing a new road or resurfacing an existing roadway.

Cross-Sectional Elements of Road

The cross-sectional elements of the road are the various components that make up the road itself. Each of these elements serves a specific purpose and helps to prepare  road cross section with complete details. Let’s explore them in detail below. 

  • Original ground level (OGL)

Original ground level (OGL) is the vertical distance from a specified datum to the undisturbed natural surface of the underlying soil. The specified datum typically means a local assumed benchmark  but can also be sea level . As high accuracy in elevation is important, data is generally collected using auto-level. However, different instruments can also be used depending on the site situation.

  • Finished Road level (FRL)

It is the final height of the roadbed after all paving has been finished. It is obtained after the geometric design of the highway. In case there is no median or divider, FRL could be at the center of a road. When the median is present, it could be different for the left and right side of the road and are provided at the edge of the median. In addition, the FRL serves as a reference point for other measurements, such as the thickness of asphalt layer.

  • Width of carriageway, paved, earthen shoulder

Based on design, there could be different elements with varying widths in a road. It can vary for single lane, multilane or expressways. It is important because it helps ensure that the road will have adequate vehicle clearance and is safe to drive.

  • Camber

Camber is a cross slope provided in a roadway. It differs for different width element based on design e.g. carriageway slope in a straight road stretch could be 2 to 3% and in a superelevated stretch of a curve, it could be higher. It helps with drainage and improves traction. 

  • Kerbs

Kerbs are the raised edges of a road that delineate the edge of the carriageway. They are typically made from concrete, granite or stone, and their purpose is to provide a safe edge for vehicles to travel along and prevent vehicles from straying off the road. 

  • Right of Way (ROW)

A road construction project’s right-of-way (ROW) is the strip of land necessary for road construction and maintenance. This strip of land typically includes the roadway, shoulder, and any adjacent property that the road construction may impact. 


We hope this article has given you a better understanding of the different elements of road construction.

Road Estimator is a powerful tool that provides users with a unique edge to generate longitudinal section and cross sections of road with extreme ease. It provides road contractors, consultants and other stakeholders the ability to quickly and accurately estimate the cost of a project. 

Check out the complete process yourself or you can try it today.

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