Sarnia Road Bridge

Most Recent Visit To Bridge: August 5, 2006

This beautiful pin-connected Pratt through truss bridge was built in 1905.

When you first turn 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 is, open to a fair amount of vehicular traffic. One of the things I like about Ontario is that they take better care of there bridges, and location is less of an issue. In Michigan, for example, a bridge like this on a road this busy would have been destroyed years ago.

 The day I was here it was 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. My wait time with a few cars ahead of me 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.

The historic society of Frankenmuth, Michigan once told me 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. I could never imagine what they were talking about until I experienced this bridge. When a car passes over the Sarnia Road Bridge, the wooden deck makes an incredible racket, which almost was hurting my ears while at the bridge. The bridge must be like an amplifier for the wood boards, which must be loose on the deck. I was glad for the experience, since now I can relate to what the Beyer Road Bridge was once like. On the other hand, it is probably better for the bridge if the boards were to be more secured on the deck.

The Sarnia Road Bridge is a pin connected Pratt through truss, built to carry Sarnia Road over railroad tracks. As through trusses go, this is a short one, having only five panels. The top chord is unusual and interesting because there is v-lacing on both the top and the bottom. The end posts only have v-lacing on the bottom. Although this bridge carries vehicular traffic, some features of this bridge are more railroad-like in style. I am unsure if this has anything to do with the bridge crossing a railroad. The main thing to note is that the v-lacing style is different. Often, railroad v-lacing does not share rivets with each piece of lacing. Instead, each end of v-lacing gets its own rivet. Also, the ends of the v-lacing are chopped off square, rather than having rounded ends. This style of v-lacing is typical of a railroad bridge. The large wood beams that make up the deck have a railroad-like feel to them also. On the other hand, the lightweight pin connected style of this bridge is something that is associated with vehicular bridges, not railroad bridges. In short, if you crossed a railroad truss bridge with a highway truss bridge, you would get the Sarnia Road Bridge. One final oddity to note about this bridge is that there is bracing rod that runs through the three middle panels of the truss. This can be seen in the photo of the bridge on this page. Having bracing in this area of the bridge in unusual.

Overall, this is an unusual bridge. It is also rare for the area, because pin connected truss bridges are in very short supply in southwestern Ontario. It is impressive to see a one-lane bridge open to a good amount of traffic, and I hope that the bridge continues to remain open to traffic.