What is the Difference Between Bridge and Culvert?

The main difference between a bridge and a culvert lies in their purpose, structure, and design. Here are some key differences between the two:

1. Purpose: A bridge is a passage of transportation (for people or vehicles) over a large body of water or physical obstruction, while a culvert is a tunnel-like structure that allows water to pass under a roadway or railway.
2. Structure: Bridges are usually linear and straight, with basic components such as superstructure (supports load), substructure (transfers load to foundation soil), and deck (transfers surface load to other structures). Culverts, on the other hand, are enclosed structures that can be semi-circular, rectangular, elliptical, or pear-shaped.
3. Design Complexity: The structure and design of a bridge are elaborate and complex, requiring a substantial budget for construction. Culverts have a simpler design, with components like concrete boxes or cells (single pipes, pipe-arches, or box sections).
4. Load-Carrying Capacity: Bridges need to support vehicular, pedestrian, and other loads, while culverts primarily carry water and sometimes light vehicular loads.
5. Span Length: Bridges generally have longer spans, while culverts have shorter spans, usually less than 20 feet. Culverts are not considered bridges because their spans do not exceed 6 meters, according to the Federal Highway Administration classifications (FHWA).

In summary, bridges are designed for transportation over large bodies of water or physical obstacles, while culverts are used for water drainage or bridging the gap over a smaller physical obstruction. The design, structure, and purpose of these two structures differ significantly, making them suitable for different applications.

Comparative Table: Bridge vs Culvert

Here is a table summarizing the differences between bridges and culverts:

Bridges are designed to provide transportation passage over large bodies of water or obstacles, while culverts facilitate the movement of water under roadways or railway lines, helping with drainage and preventing floods and erosion. Bridges require a deep foundation and have a linear structure, whereas culverts do not need a deep foundation and can have various shapes like semi-circular, rectangular, elliptical, or pear-shaped. Bridges allow traffic movement only over their decks, while culverts accommodate roadways both under and above their decks.