I'm looking to begin an HO scale layout. I'd like to have a bridge at some point in the layout, but how much room do I need? Some layouts I've seen take up 4 feet to for the full length of the trestles and bridge. Is there a guide to determine the best rate of incline?
This link has good info for you.
http://www.building-your-model-railroad.com/grades-and-clearances.html
Best to stay 3% grade or lower.
Jerry
bf65-
You can have bridges of any length. It all depends on the size of the gap between two solid places for your roadbed. That can be anything from an inch or two over a creek to several feet if you must span a huge canyon or the entrance to an ocean bay. You can limit your bridges to short trestles over a marsh or road overpasses or make huge iron or steel bridges arching over major physical obstacles. Your bridges can be fixed or move to the side or bertically to permit ships to pass. Your bridges can be short or long, tall or low, at lofty elevations or minimal ones. It's your railroad and your world so you can do whatever you want. Just make sure that your bridge makes sense in its context. Railroads did their level (sorry) best to avoid grades so they didn't hesitate to use fills, cuts and bridges to keep their tracks flat. So make certain you have running water or a genuine gap to justify your bridge.
-- D
If you don't want to get into the classic "Up & Over" figure-8, which has almost all the track either going up or down except short sections at the top and bottom, there are a couple of options.
A. Use 2in thick blue or pink insulating foam as a base for you layout. This allows you to keep the track flat, yet makes it very easy to carve out rivers, cuts, etc., to justify bridges and/or trestles.
B. Use Woodland Scenics foam risers as a base for the track, leaving gaps where you want to install a bridge or trestle. Using the foam risers allows rolling hills to easily be created using wadded up newsprint and plaster cloth between the risers. This allows the track to stay flat, while creating the illusion track is going up and down. The risers are available in heights of 1/2", 3/4", 1", 2", and 4". There are also inclines available to transition between riser heights if you actually want to add grades, without the full "up & over" look.
Len
Thanks for all of the replies! This is a big help!
Here's another site with an automatic calculator that seems easier.
LIRRMAN
www.veloroutes.org/tools