What’s the Difference between a Bridge and a Viaduct?

difference bridge viaduct

Here is another difference that seems minimal when speaking or writing, but do you know the real difference?
Could you explain to someone in which cases he should use “bridge” or “viaduct”?

What’s the difference between a bridge and a viaduct?
There is not a big difference between these two structures
We generally consider that a bridge is smaller
A viaduct is often a gigantic structure, by its size, height or width

I will explain more deeply this difference, with details and images to be sure everything is clear for you

A bridge

Definition

A structure carrying a pathway or roadway over a depression or obstacle (such as a river)

Merriam-Webster

Please note that the obstacle that the bridge allows us to avoid doesn’t matter with the structure’s name
You can have a bridge over a river, a road, a specific relief, etc.

Pictures

Here are a few pictures of famous bridges:

Note about old structures

You may also notice that all historical structures, built before the 20th century, are generally called “bridges”
Even the San Francisco Golden Gate, with almost 9,000ft (2.74 km) is considered as a bridge

Bridge classes

I’ll now give you some categories we have created to differentiate bridges

By materials

Resources used to build bridges can be very different between a bridge and another. It mostly depends on the construction date

  • Stone bridges: We find examples dated of prehistorical times, they are the first bridges we know (with wooden bridges)
  • Metal bridges: Even if there are some ancient bridges in metal, most of them were built with the railways development
  • Concrete or reinforced concrete bridges: The most recent bridges are now built in concrete

By construction type

We can also find a category for each bridge, depending on the construction type

  • Ark bridges: As the name says, these bridges are built with several small arches (like the Paris bridge I share in the pictures)
  • Arch bridges: Same thing, but this time with only one arch
  • Beam bridges: Most modern bridges are beam bridges, with pillars spread over the entire length to support the bridge
  • Hanging bridges: You probably have in mind the most dangerous monkey bridges and wooden bridges. But the Golden Gate is also a hanging bridge
  • Cable-stayed bridges: Close to the hanging bridges on which there are pylons (above the roadway) supporting the rest of the bridge through cables
The Golden Gate bridge, San Francisco

A viaduct

Definition

A long elevated roadway usually consisting of a series of short spans supported on arches, piers, or columns

Merriam-Webster dictionary

As I said in introduction, a viaduct is a larger structure
This quote insists on the structure length

Pictures

Everyday language

Some people, mainly in specific jobs, can have different rules to use the viaduct word rather than bridge

For example, in some countries, the railway companies are always using “viaduct”. A train never pass on a bridge, but on a viaduct
Same thing for the road, employees from the road networks have their definition. They use “bridge” for a structure that is over a river, and “viaduct” to cross an entire valley or a dry area.

So even if you know the theoretical difference between a bridge and a viaduct, you can still find people using them differently 🙂

Viaduct and aqueduct

The last thing I need to explain you is the difference with an aqueduct

Finally, would the good definition not come from the Latin origins of the word?
Indeed, in this case the difference is simple:

  • Aqueduct = aqua (water) + duc (drive): it’s a structure conveying water between two points
  • Viaduct = via (road) + duc (drive): this time, we talk about a structure allowing to have a road over an obstacle

So, and the bridge?
Good question 🙂
I will come back to this at the end of the post

Differences between a bridge and a viaduct

We can now try to compare everything we saw, and summarize everything here

Definition

When we only read the dictionary, the biggest difference seems to be the structure size, mainly its length
A viaduct should be longer than a bridge

Everyday language

When we watch how people how these two words (bridge and viaduct), we can see that everyone has a different definition
So we can’t really find the solution here

Bridge, viaduct and aqueduct

The problem seems even more complex when we add the aqueduct word into the discussion

For Wikipedia, the difference is that a viaduct is to allow human beings to pass an obstacle, and the aqueduct is to convey water over an obstacle

So the bridge is a structure category, including viaduct and aqueduct
A viaduct is a bridge, and a bridge can be a viaduct or an aqueduct

Synonyms

I even saw dictionaries saying that viaduct and bridges as synonyms
And why not?
If a bridge is either a viaduct or an aqueduct, but we don’t use aqueduct anymore now, is there still a difference between both?

Conclusion

I think that’s it for this difference, we have seen many things today
The official difference seems simple (they are not comparable), but the words usages make the explanation a bit difficult

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