Is a given railroad span a bridge, a trestle or a viaduct?
After a lot of railroad reading and looking at many thousands of captioned photos, these terms seem to be used almost interchangeably. I have seen the exact same picture where the structure is called both a bridge and a trestle.
Is there a definiitve difference in terrain, construction, engineering, or use?
Thanks,
Balboa
Trestles are often wood, have several bents, or legs, made up of poles or collums with cross braces through the collums and heavy top beams tieing the legs of the bent together.
The deck of a trestle rest on these top beams…
Bridges are steel, wood or stone/concrete, designed to sit atop pillars, poles or pilings, supported at the ends, often by abutments.
Bridges have less number of supporting structures, of thicker or more sturdy constructon than trestles.
Viaducts are arched stone structures, designed originaly to carry water in an above ground trough.
The basic design used arches through out, often arches on top of arches, and allowed the force of gravity to induce flow in the water.
Later, adapted to foot and vehicle traffic, then automobile and rail traffic, the most obvious feature of a viaduct is its lenght and its construction based on the arch.
Some steel viaducts, designed to carry auto and train traffic do exsist.
MudChicken will have a better explaination, but just so you know, most of the time writers have no idea there is any difference, a bridge is a bridge is a bridge, or viaduct, which ever word suits their fancy.
Ed
a little bit of both. Some long spans are bridges, other viaducts. For whatever reason, trains backing into the old Milwaukee Road depot in Minneapolis crossed over the Washington Ave. “viaduct”…so it may be a cross of railroad/personal slang and technical jargon.
But at the same time, we have the Main Street Viaduct, about a mile long, over the old(now gone) Hardy Street yards and Buffalo Bayou, designed in the late 1930s, strictly for automobile traffic.
It is a series of pre-stressed concrete arches.
Ah, where the mudchicken when you need him?
Ed
…I don’t have the answer how railroad structures are catagorized but can make a comment: Near my home area in Pennsylvania…near Meyersdale, we have a structure that was part of the Western Maryland RR…{which was abandoned in the early 70’s}, and it is a 1900 ft. long by 100 ft plus high “bridge” that carried the RR across the broad valley and across a river and the former B&O RR. It is structured of steel…All of it…It was made to hold 2 tracks but just had one. The structure is now part of the Allegheny Trail and is really great with a brand new cement floor and wire mesh side railing. It has always been called: Salisbury Viaduct. So, this one is metal and called a “viaduct”. One might go to “Google” and enter in that name and find a photo of it…it’s been around since the early 20th century and pretty well known in rail circles.
Trestles can be made of steel, seen plenty on the N&W.
Ok, did the dictionary thing…
Here goes.
Bridge: A structure spanning and providing passage over an obstacle.
Trestle: A horizontal bar held up by two pair of divergent legs and used as a support.
A framework of vertical slanted supports and horizontal crosspieces supporting a bridge.
Viaduct: A series of spans or arches used to carry a road or railroad over something, such as a valley or road.
So, a viaduct can have several bridges in it, supported by trestles.
Bridges can be supported by trestles.
Both bridges and viaducts can cross obstacles, but it would appear that viaducts use more than one span, and cross larger areas?
Or, are viaducts and trestles the supporting structure, to carry the bridge?
And depending on what support is used, that is what defines the name applied?
Now we really need a engineer, of the civil kind!
Ed
Ok, so lets add to the mix.
What is a causeway?
At first blush, the old Galveston causeway would appear to be a viaduct, it is a series of arches, that cross a long distance, with a drawbridge in the middle, designed to carry a railroad and a single roadway across Galveston Bay.
It is almost 100 arches, made of concrete.
So what makes it a causeway instead of a viaduct?
Because it crosses water instead of a valley?
Ed
Wilmington DE. has a Viaduct built by the PRR. It is now on the National Historic Registry. The Viaduct is several miles long and is really designed to only elevate the tracks above the street and eliminate grade crossings. The spans are not very long and the viaduct has several bridges that cut the continuous succession. The bridges allow street traffic to flow underneath.
Is this a true viaduct?
Good grief. Never really thought about it! How would I (I’m a civl (sometimes – sometimes not so civil!) engineer who does these things now and then…) categorise them. Trouble is, I think, that the terms really aren’t exclusive. Some are.
Culvert: I would never use the term culvert for anything except what was fundamentally a pipe (need not be round) through a fill. In terms of loading and design, the fill is carrying the track, not the pipe – although the pipe (or box or whatever) has to be designed to take the load and distribute back into the fill. Culverts don’t have foundations.
I would confine the term ‘causeway’ to a type of long pile trestle over a large body of water or a swamp or somesuch. Causeways, which are hideously expensive to maintain, are used instead of fills in instances when it is necessary to let the water move pretty freely from one side to the other. They are not used in particularly deep water, and may have one or more bridges to let things (like boats!) other than water pass underneath. In the good/bad old days, causeways were often filled later – or even intended to be filled from the beginning, and now and then a very long fill across a body of water will be referred to as a causeway (e.g. the Lucin Cutoff across Great Salt Lake).
Trestles and Viaducts. I would tend to use the term ‘trestle’ for a structure which consisted of a number of short span bridges supported on steel, wood, or concrete ‘bents’ (structures of a number of poles set vertically, holding up the ends of the short spans) which are braced from bent to bent at intervals by other beams of steel or wood to prevent sway. Generally in a trestle all the various beams and columns and what have you are pretty small members. Viaducts, on the other hand, would – as Mark noted – have longer spans between the supporting columns; the structure is very often (not always) mass masonry (stone or concrete) and – perhaps most important – the support piers or bents are not brace
Anything that carries/ drains water over or under a railroad is considered to be a bridge as is any structure that separates trains from other modes of traffic.
-Railroad Engineering Point of View (i.e how it is labelled in R/W and track maps)
…One of the bridges, viaduct or whatever that helped span the route out to Key West on Flagler’s RR was seven miles long and it consisted of masonry arches planted in rather shallow water. I don’t remember what the official name was for those structures. But massive, they were…Of course they carried highway Rt. 1 years later after a hurricane destroyed the RR. It was a weird feeling drivng that far out over the water.
After reading all the answers and submitting some comments of my own I believe the answer to the original question…especially to define a large structure such as I have in an above post…can be defined as either a viaduct or trestle…Looks like both apply.
…And the structure that connects the Space Center to the Titusville, Fa. area is called a causeway and it for the most part is a land fill upon which a road is built…{several miles}, but does contain a “draw bridge” to enable boats to pass through the site.
As for trestles, some of the original wooden structures out west certainly weren’t “low” to the ground…Perhaps some were a hundred ft or so above the terrain they crossed at a high point even though they did not provide great “open” clearance space under them because of all the bracing.
…Didn’t TRAINS have an article on that railroad area back some months or maybe a year ago…?
…Mark, that Grangeville article is pretty wild. How did that railroad EVER make money with all that hardware to upkeep…? That must have been some ride and scenery to observe crossing that line…especially when it was all green. Yes, I like the green one better.
Here’s a link for the Tunkhannock Viaduct:
http://www.bridgemeister.com/pic.php?pid=796
Build by the DL&W, and today carries the CP (D&H) line to Scranton.
It’s a quite impressive structure.
…That is an awesome structure…One wonders how they ever got that much concrete in one place to build such a monster…
Being a bridge engineer, bridges are classified as individual spans over 20-ft in length. Below that span, they are culverts, pipe, or other names. A trestle is normally (exectptions to the rule 85+%) would be a series of short spans. A viaduct is an grey term but would be another name for a trestle. Another question, is a bridge an overpass or underpass? It depends on which is the major route. Major road over- overpass, major road under - underpass.
I have wondered if a structure is defined as a viaduct by how many columns it has at the same spot. i.e. a trestle has two supports that are braced together to support the structure. Take the Linn Cove Viaduct on the Blue Ridge Parkway for example:
I’ve wondered this myself.