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Sarnia Road Bridge

Sarnia Road Bridge

Primary Photographer(s): Nathan Holth

Bridge Documented: August 5, 2006

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Facility Carried / Feature Intersected
Sarnia Road Over Railroad (Canadian Pacific)
London: Middlesex County, Ontario: Canada
Construction Date and Builder / Engineer
1890 By Builder/Contractor: Unknown
Rehabilitation Date
Main Span Length
90.0 Feet (27.4 Meters)
Structure Length
90.0 Feet (27.4 Meters)
Roadway Width
Not Available
1 Main Span(s)
Inventory Number
Not Applicable

Historic Significance Rating (HSR)
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Bridge Documentation

This bridge is in storage!

Bridge Status: This heritage bridge was replaced , but was reportedly put in storage, available for reuse.

View An Official Statement Of This Bridge's Heritage Significance, Prepared By A Consultant For The City of London

View An Official Statement Of This Bridge's Heritage Significance, Prepared By A Consultant For The City of London

View Video of this Bridge Being Lifted Off Its Abutments.

View Video Showing The Sights and Sounds of This Bridge In Use

The Importance and Feasibility of Preservation

This beautiful pin-connected Pratt through truss bridge was built ca. 1890 in St. James, Manitoba and was relocated to its current location in 1909, according to the heritage assessment for this bridge. The bridge has been closed to traffic, and this important heritage bridge is currently at risk for demolition, as its replacement is planned. Currently, the plan is to replace this bridge, with the heritage bridge potentially being placed into storage for potential reuse. Placing a pin-connected truss bridge into storage is one of the least expensive and simplest ways to prevent a heritage bridge from being reduced to scrap metal. As such, the concept of storing the bridge should not be a "maybe" it should instead be written into the official project plan. HistoricBridges.org encourages the city to instead explicitly state that this bridge is not to be demolished. This bridge was evaluated to have high heritage significance, and HistoricBridges.org strongly concurs with that assessment. It is an irreplaceable structure, and a low-cost option has been identified to prevent the destruction of it.

Pin-connected truss bridges are exceedingly rare in Ontario and they are becoming even more rare as examples elsewhere are demolished. Canada does not have any legislation that explicitly protects and funds the preservation of heritage bridges. It is up to local municipalities like the City of London to realize the importance of heritage bridge preservation and to undertake such preservation. As mentioned, pin-connected truss bridges are thus rare in Ontario. London is an anomaly in that it is a city that has more than one pin-connected truss bridge, the other being the King Street Bridge. Most cities do not have a single example. London actually has one of the largest numbers and widest varieties of heritage bridges of any city in Ontario. Does this mean that one bridge is more expendable? Absolutely not, in fact it suggests that the preservation of each example is essential because in London their exists a unique opportunity to develop "heritage bridge tours" which could be used to generate tourism revenue as visitors could come to London to visit its collection of heritage bridges.

HistoricBridges.org recognizes that funds to rehabilitate and preserve heritage bridges are hard to come by. As such, demanding that the Sarnia Road Bridge be relocated and rehabilitated at a new location, perhaps for pedestrian use, immediately as part of the replacement project may be inappropriate. Instead, carefully marking, and disassembling the parts of the bridge and placing them in storage at a secure location for reuse in the years to come represents exactly the sort of compromise that recognizes the funding challenges that the city faces, while also ensuring that an irreplaceable heritage bridge is not destroyed. Once in storage, the cost of keeping the bridge is zero and a bridge of the type and size of Sarnia Road Bridge could be stored in the corner of a maintenance garage or yard. Pin-connected truss bridges look big when they are assembled and standing, but when dismantled and in storage it is truly amazing how little space they take up. The Frith Road Bridge is a good example of a bridge placed in storage. Once in storage, the city can take all the time it needs to find a way to get the bridge restored and re-erected at a new location. A wide variety of options would be available to accomplish such a goal. The city could undertake the project itself, perhaps to improve or expand a non-motorized trail. Alternatively, the bridge could be offered to a third party for reuse. The bridge could be reused by third party or city in any number of ways. The Sarnia Road Bridge would be a perfect substitute for any planned non-motorized crossing, where the original plan was to install an ugly "mail order truss bridge" such as a Continental Bridge Company bridge. Instead of an ugly, non-descript cookie-cutter bridge, the non-motorized facility gains a beautiful cultural asset. The South County Line Bridge is a good example. Adaptive reuses for a bridge are as broad as the imagination can go. For example, the London Advisory Committee on Heritage suggested the bridge could form the skeleton for an enclosure that would protect Engine 86, a train engine that sits in front of Western Fair. Another low-cost option is to simply erect the bridge so that it sits on the ground, often described as an exhibit, since like a museum exhibit, the bridge does not function, yet it stands for people to observe and interpret. The Moneek Bridge is an example of this solution.

There are so many ways that the Sarnia Road Bridge could have a new life that the demolition of this bridge should not even be part of the conversation. If needed, the knowledge base and communication network of Historicbridges.org stands ready to help London learn how to avoid the demolition of this bridge, and keep the costs of doing so low. Feel free to send an email if there are questions or concerns.

Sarnia Road Bridge Significance: Rare and Unique Details

The Sarnia Road Bridge is both historically and technologically significant as a rare pin-connected truss bridge, and an equally rare pre-1900 truss bridge. Both characteristics are very rare among surviving heritage bridges in Canada. As through trusses go, this is a short one, having only five panels. The bridge has been damaged several times over its service life, and there are associated repairs at the end posts as a result. Aside from changes associated with those repairs, the bridge appears to retain good historic integrity. The main loss of original material is the replacement of the floorbeams, however this is considered a minor alteration because floorbeam replacement is usually considered acceptable work as part of a preservation project. As such, the bridge is evaluated to have good historic integrity.

The Sarnia Road Bridge is further significant for its highly unusual construction details. Some of these unusual details appear to be the result of this bridge being designed by a railway, rather than the more traditional highway bridge that would have been designed by one of the many highway bridge companies that operated in the late 19th and early 20th Century. The heritage assessment for this bridge recognized this and even supposed that the bridge originally carried trains, and when moved to London was widened and converted to serve highway traffic. HistoricBridges.org is unsure if this is really the case however. While the members of the Sarnia have details that are normally associated with railway bridges, the actual size of the members on the bridge is consistent with a highway bridge. Railway bridges usually have far more massive members, like the bridge on the North Branch Thames River. Based on the construction of the bridge, it would also be possible that this bridge always served as a highway over railway bridge, and the reason for the railway details on the bridge is simply because it was designed by the railway. Even though they may carry a highway, bridges that cross a railway often still fall under the responsibility of the railway to construct and maintain.

The unique details on the Sarnia Road Bridge include the type of v-lacing on the vertical members, end posts, and top chord. The lacing bars are not rounded at the ends, but instead are simply cut off and so they have sharp corners. This type of lacing is far more common on railway bridges than on highway bridges. The struts (sway bracing) of this bridge also have knee braces that while attractively curved, are positioned as such that they end abruptly and do not blend into the actual strut. This aspect, as well as the v-lacing design both suggest that less concern was placed on the aesthetic quality of the bridge, compared to the typical highway bridge which might be more aesthetically pleasing, having been designed by a bridge company who would want to advertise their bridges and company as better than their competitors. In this way, the bridge further expresses the fact that it was designed by the railway, who couldn't have cared less what their bridge looked like. There are other details that are unusual on this bridge but do not directly point to the railway as a reason for their existence. The bridge has v-lacing both on top of the top chord and under the top chord. This is very rare. Usually, the top of the top chord would have a cover plate, like the end post of the Sarnia Road Bridge displays. Nearly all pin-connected truss bridges will have cover plate on top of the top chord and end post. Presumably, the cover plate provides greater strength to the beam, however the use of v-lacing on top reduces the areas where one piece of metal lies against another piece of metal, and so deterioration by pack rust is drastically reduced with this top chord design.  The other unusual feature of this bridge is the lightweight rod which proceeds diagonally from the top chord / end post connection down to the middle of the truss web, where it runs horizontally through the web. This detail was common on older bridges built by the Wrought Iron Bridge Company of Canton, Ohio. Finding this detail on this bridge, obviously not associated with that company, is quite unusual.

2006-2009 Discussion of Bridge

When you first turned down Sarnia Street, you might think that a road as busy as it is could never have a one-lane pin connected through truss bridge on it. The five ton weight limit sign is the only thing that would suggest an old bridge was down the road. Nevertheless, here the bridge was open to a fair amount of vehicular traffic until its closure in 2008. It was highly unusual to see a one-lane pinned truss on such a busy road. However time finally caught up with this bridge after it suffered damage from somewhat less than intelligent truck drivers who disobeyed restriction signage and attempted to cross the bridge. Now the bridge's fate is uncertain, despite its obvious and verified heritage significance and feasibility for being relocated (or bypassed) and the recipient of an in-kind restoration for pedestrian use.

 The first time this bridge was visited it was open to traffic and not uncommon to have a few cars lined up at either side to get across the bridge. With no stoplight to control traffic, the bridge is treated like a four-way stop, with each side taking turns. The wait time with a few cars ahead going across this bridge was less than that of the average red light on a stoplight. This bridge teaches a lesson to all the road commissions in Michigan who say that rural one-lane truss bridges that carry two cars an hour are unsafe. Here is a one-lane truss bridge on a paved suburban road with moderate traffic and no definitive traffic control device like a stoplight, and the bridge does its job fine, except for those trucks that disobeyed the restriction signage.

The historic society of Frankenmuth, Michigan once told Historicbridges.org that in the old days, the Beyer Road Bridge had a wooden deck that was so loud when you drove across it that the noise could be heard for miles. One could never imagine what they were talking about until the Sarnia Road bridge was experienced. When a car passed over the Sarnia Road Bridge, the wooden deck made an incredible racket, which almost hurt the ears while standing on the bridge. The bridge was like an amplifier for the wood boards, which were loose on the deck.


Photo Galleries and Videos: Sarnia Road Bridge


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Structure Details

Original / Full Size Photos
A collection of detail photos that document the parts, construction, and condition of the bridge. This gallery offers photos in the highest available resolution and file size in a touch-friendly popup viewer.
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Structure Overview

Mobile Optimized Photos
A collection of overview photos that show the bridge as a whole and general areas of the bridge. This gallery features data-friendly, fast-loading photos in a touch-friendly popup viewer.
Alternatively, Browse Without Using Viewer


View Photo Gallery

Structure Details

Mobile Optimized Photos
A collection of detail photos that document the parts, construction, and condition of the bridge. This gallery features data-friendly, fast-loading photos in a touch-friendly popup viewer.
Alternatively, Browse Without Using Viewer


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