Thanks everyone.  As I said before this was my first bridge and I found I liked the challenge.
I spent the day fitting the bridge into the layout. But first I had to add a small piece of benchwork.

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I cut a piece of plywood 3X11" and fitted it into the gap below. I temporarily screwed it to these two supports from the top before I secured it from below to make sure it would be flush with the rest of the top deck. 

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Then I laid the bridge back in and lined up where I would cut the flex track.

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The bridge is now fitted. The rail joiners on both sides are loose so I can remove the bridge so I can fit the piers and abutments, but you get the idea.

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Now I can measure and scratchbuild the piers and abutments. I'm figuring on a pair of joined trestle bents under the bridge 'feet' and a taller bent against a retaining wall at each end.

here's another photo that might help with abutments . 
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Jim

Thanks Jim. I figured out the piers for the bridge:

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As I mentioned I decided to build two bents and join them together with cross bracing  and lateral beams. I looked at a few pictures and photographs and this looked the most convincing to me.


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And with the bridge supported.


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And on the layout. One pier is snug against the bridge and the ground, the other needs just a bit of shimming for a tight fit.

here's a photo of a prototype using then same type of support , bridge looks great . 
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Jim

Thanks Jim. Photos like that and a few old Model railroader articles have been a big help.
I finish the project this morning, building the trestle bents that will support the approaches. 

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It took longer to design the bent than to build it. I also had to build one slightly longer than the other so each was a custom fit.

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I also made some retaining walls to go behind the bents using some scribed siding. I had just enough of the Micro-mark stain to complete everything.

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And with everything in place. Scenery to follow later.

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As an epilog I was looking at the howe truss bridge that my father built for me and realized that he hadn't actually finished it.

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The bridge was complete but for some reason, the decking was never built. So that was my next project. 

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I was lucky enough that I had a section of built decking that fit the bill. Another modeller gave this to me years ago for some reason so I decided it was better to re-use it than to scratchbuild a whole new one. I did have to shorten it and relay the track and guard rails.


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My only other snag was I had added some temporary bridge abutments that now had to be removed so the bridge would sit in it's proper place. 

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another good looking bridge and another proto pic.
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Jim