I have just completled my first major scratchbuilding project, what is called a “tier trestle.”

A tier trestle is the term recently given by historians to the hastily built trestle bridges on the Burma Thailand Railway. ( I am modelling a freelance post-war version).
Complete details and definitions on my blog at
http://robinrowland.com/wns/2007/01/building-tier-trestle-bridge.html
The blog also explains why this type of bridge may be of interest to narrow gauge and/or logging railways or railways that have “temporary” lines.
Robin