Mile Load Road Bridge

Given that the original location is in southern Iowa, I’m going to hazard as guess that this is a through truss that was inverted.

Brilliant work, as always, John

I'm not sure whether to make anything of this but the 1948 topo shows the kink in the road and a 562 benchmark. The 1925 maps shows a straight road and a 553 benchmark. This makes me think the current bridge went in during this time period on a slightly different alignment.

Thanks Tony! I've been trying to identify such cases involving trusses and girders. They used to be everywhere, as spans not strong enough for railroad use found their way onto road overpasses, particularly on mainlines. Based on 1918 track profiles for Wisconsin, we've lost somewhere around 95% of the original population of these unique structures, and unfortunately these are often constructed of 1880s and 1890s pieces.

I think you're spot on John... Neat bridge!

This bridge appears to be a rare deck truss example of a recycled railroad bridge reused on an overpass.

I walked across the bridge twice and took a bunch of photos before I finally spotted evidence of a truss. And then it was a glimps through the trees. So I hiked down and around to get a view of the side and underside.

This is an odd bridge for automobiles. It feels more like a railroad bridge - so it makes sense it was built by the railroad.

Things I found odd about it:

- Narrow deck truss

- Timber bents and timber cribs substructure

- Timber floor beams

- Timber deck _without_ runners

- The approach spans are not in line with the main span. The south approach is pretty close, but the north approach is definitely not resulting in a curved appearance.

The deck has a very noticable dip in both approach spans. With it's listing as a truss, these dips made me very nervous! But the truss span is straight and level. It appears the bents under the approach spans have settled causing the dips.

The truss is pin connected, with 4 to 6 upset eye bars per panel. This seems heavy duty - but then the distance from the bottom chord to the top chord is only about 8 ft. (2.5 m) I think the short verticals means more tension on the bottom chord...

For future visitors, there is a road off of Mile Load Rd a bit south-east of the bridge that has a grade-level crossing of the railroad tracks. And keep an eye out, there's a lot of poison ivy.

Photos taken 11-4-09.