Structures

Railroads require fairly flat and level track in order to operate. Generally speaking, the track should have no more than a 2% grade, meaning that it can rise/fall no more than 2 feet for every 100 feet of distance (equals 1/4" of rise/fall per 48" of distance).
But terrain is rarely flat, so railroads must bridge over (or fill in) low spots and tunnel under (or excavate) high spots.
Real railroads try to avoid tunnels and bridges because they're expensive to build and maintain, but I'm doing the reverse - finding any excuse to build them - because I think they're interesting!

Here are the structures that I'm currently working on and/or planning to build:

Item	When Built	% Complete	Description
Deck Truss bridge	10/03 - 6/04	100	20 feet long, crosses a small, seasonal stream
Covered bridge		0	? feet long, based on a local historic covered bridge
Trestle		0	100 feet long (!) and 8 feet high
Tunnel	9/03 - ongoing	10	50 feet long, curved, cut-and-cover
Retaining wall	10/04	100	30 feet long, routes track around a large tree