I built two trestles from scratch, just to see how they'd look, before I built one to actually put on a layout.
I model in N scale, but the principles are the same regardless of scale.
I made a drawing of the bent structure on a sheet of styrene, then laid a piece of the wood to be used for the pilings in place and used small styrene strips, glued down as guides.
Here are two templates I made, with the finished bent sections.
The holes you see in the template are there to prevent gluing the wood to the template, I discovered the need for the holes after my first attempt. For glue, I used gap filling AC (Super glue).
As mentioned in earlier posts, stain or paint the wood before construction to get a good finish. It also helps seal the wood and prevents the AC from soaking into it. When assembling, small amounts of glue work better than large amounts. I tested the strength of one two bent section of the trestle. It supported two ten pound test weights. For your HO trestle, you could drill the bracing for insertion of Grandt Line bolts, to give it a more authenic appearance.
A good source of information is Bridges & Trestles, Model Railroad Handbook No. 33, from Kalmbach. It has everything you ever wanted to know about the subject and some things you might not.
Here is the doulble track trestle I built for my neighbor's N scale layout.
Micro Engineering makes flex track with the correct tie spacing with guard beams and guard rails for the trestle. The track also comes with platforms and water barrels. I didn't use these on the trestle I built, because there's no steam power on my neighbor's layout.
Here's a view taken from a slightly higher angle with no train on the trestle.
I hope this gives you some helpful ideas.
N Scale UP in the 60's
Turbines are so cool