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View Full Version : What's the DIfference between a causeway and a bridge?


Hypno-Toad
11-08-2004, 08:57 AM
Hey Y'all,

Down here in Lee County, Florida we have a little bit of a situation. Many of our gulf islands are only road accessible via the "Sanibel Causeway." It is a string of three spans that hop from the mainland to Sanibel Island via a pair of spoil islands. Two of the spans are low with the third having a drawbridge.

There is a great deal of contoversy over whether or not the bridges/causeway should be repaired or replaced. The City of Sanibel wants the original causeway repaired and most definately not improved in any way. (That would let more people onto the island, see?) Lee County wants to replace it with a high span bridge that would allow traffic to flow without the delay of passing boats. The seasonal traffic problem that is now gearing up becomes worse each year, so things are coming to a head.

Now, throughout this controversy I've been wondering why it's called a causeway and not "The Sanibel Bridge." Some of my coworkers think that it's because there are three actual bridges going from island to island ane the term causeway means the whole system. Others say that it's simply a naming convention, pointing out that a causeway need not go over water. A raised berm can be a causeway as well. Some say that the difference is in the construction: a solid dyke versus a truss, suspension, or other "assembled" structure.

Others feel that it is defined by it's function. A causeway is a low, constant-elevation "road" over a lake like the Mexica (Aztecs) had at Tenochitlan while a bridge is a structure that connects two higher elevations over a lower area such as a valley or river. My dictionary defined the terms synonomously.

Any civil engineers out there know the answer? The PEs that I know weren't sure.

Philster
11-08-2004, 09:22 AM
A causeway could consist of bridges, raised roads, etc. A bridge is something you can point to....a causeway is a highway, which may use bridges, etc.

Donovan
11-08-2004, 09:27 AM
Hey Y'all,

Down here in Lee County, Florida we have a little bit of a situation. Many of our gulf islands are only road accessible via the "Sanibel Causeway." It is a string of three spans that hop from the mainland to Sanibel Island via a pair of spoil islands. Two of the spans are low with the third having a drawbridge.

There is a great deal of contoversy over whether or not the bridges/causeway should be repaired or replaced. The City of Sanibel wants the original causeway repaired and most definately not improved in any way. (That would let more people onto the island, see?) Lee County wants to replace it with a high span bridge that would allow traffic to flow without the delay of passing boats. The seasonal traffic problem that is now gearing up becomes worse each year, so things are coming to a head.

Now, throughout this controversy I've been wondering why it's called a causeway and not "The Sanibel Bridge." Some of my coworkers think that it's because there are three actual bridges going from island to island ane the term causeway means the whole system. Others say that it's simply a naming convention, pointing out that a causeway need not go over water. A raised berm can be a causeway as well. Some say that the difference is in the construction: a solid dyke versus a truss, suspension, or other "assembled" structure.

Others feel that it is defined by it's function. A causeway is a low, constant-elevation "road" over a lake like the Mexica (Aztecs) had at Tenochitlan while a bridge is a structure that connects two higher elevations over a lower area such as a valley or river. My dictionary defined the terms synonomously.

Any civil engineers out there know the answer? The PEs that I know weren't sure.
Not a civil engineer, so I could be talking out of my ass, but I thought the term causeway used for land based 'bridges' over or on top of wetlands - the bridge is over land, but over land that really isn't conducive to overland travel. Most of the causeways I read about are referring to 'ancient causeways' (i.e. archeological sites) for foot travel and are not necessarily raised above ground - it could be that it was a long line of planks at ground level, but they keep the travellers feet dry. I am assuming in this case, the causeway crosses over wetland, open water, and dry land?

Donovan
11-08-2004, 09:28 AM
and philster jumped in ahead of me - come to think of it, i think his decription of a causeway is probably better than mine.

BobLibDem
11-08-2004, 09:35 AM
Typically we use the term causeway to refer to a road that lies on fill placed in the water. Generally you'll see them in swamplands or marshes, sometimes over sections of lakes.

Legally, the definition of a bridge is given in CRR 650.403 (http://a257.g.akamaitech.net/7/257/2422/14mar20010800/edocket.access.gpo.gov/cfr_2002/aprqtr/23cfr650.403.htm)
Bridge. A structure, including supports, erected over a
depression or an obstruction, such as water, a highway, or a railway,
having a track or passageway for carrying traffic or other moving loads,
and having an opening measured along the center of the roadway of more
than 20 feet between undercopings of abutments or spring lines of
arches, or extreme ends of the openings for multiple boxes; it may
include multiple pipes where the clear distance between openings is less
than half of the smaller contiguous opening.

Polycarp
11-08-2004, 11:47 AM
A causeway is a roadway constructed to keep the roadway surface from being wet, either by the use of elevation, levees, bridging, or whatever. It may or may not cross open water by a bridge. A bridge is a specific structure used to take a roadway (or other mode of progression, as a railway or a pedestrian walkway) across a particular body of water. (Note that a culvert takes a small body of water under a roadway -- the distinction apparently being that a bridge leaves land surface while a culvert is covered with rock or soil and the roadway built on that.)

Philster
11-08-2004, 12:22 PM
Alexander the Great built a causeway by just piling stones on top of eachother. If the middle of the causeway had a bridge, you could still point to the whole heap and call it a causeway. You might point to the occassional bridge and note there are bridges on the so-called causeway.

Building up a highway with stone and gravel and just using mass to overcome nature would be a causeway. Bridges are particular structures, so a bridge usually (operative word) wouldnt be called a causeway.

msmith537
11-08-2004, 01:19 PM
So how is that different from a 'viaduct'?

Polycarp
11-08-2004, 01:35 PM
So how is that different from a 'viaduct'?

I don't know viaduct -- Vhy not a goose?

Seriously -- a viaduct is a raised section of roadway which may have nothing to do with water. There's a thread in MPSIMS from a couple of months back about a French superhighway that is being routed across a valley cutting through a plateau by keeping it at the plateau level by a very high viaduct. (The fact that the viaduct crosses several km of valley and one small stream does not, IMO, make it a bridge across that stream -- the purpose of the viaduct is enable the road to cross the valley at the level of the plateau, not specifically a stream crossing; that's incidental to the road.)

A causeway may or may not be raised on pilings, etc., but will cross wet areas -- either open water or saturated-soil wetlands -- while I'd say that it's essential to the definition of a viaduct that it be elevated by openwork engineering structures and it need not cross water or wetlands.

The Chicago and Pulaski Skyways, and I-81 elevated above Almond St. in Syracuse NY, are examples of viaducts with no significant water crossings. On the other hand, every example of a causeway is in some way connected to ensuring that the roadway is not subject to the water-related conditions of the surrounding terrain.

SanibelMan
11-08-2004, 01:43 PM
Nothing to add to the causeway/bridge debate, but I just wanted to say "hi" to Hypno-Toad. Whereabouts in Lee County are you from? (Three guesses where I'm from and the first two don't count.)

GorillaMan
11-08-2004, 03:25 PM
Viaducts, at least originally, were a series of arches, a bridge being a single arch. Without such arches or other bridging techniques, it's not a viaduct.

Hypno-Toad
11-12-2004, 01:07 PM
Nothing to add to the causeway/bridge debate, but I just wanted to say "hi" to Hypno-Toad. Whereabouts in Lee County are you from? (Three guesses where I'm from and the first two don't count.)

Forgot to say "hi" back at you. I'm in the might metropolis of Fort Myers.

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